MKSH
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BSD mandoc
MirBSD
NAME
mksh
sh
- MirBSD Korn shell
SYNOPSIS
-words
[-
+abCefhiklmnprUuvXx [-
T [
! tty
]
]
|
-
]
[-
+o option
]
[-
c string |
-
s |
file
[
argument ...
]
]
builtin-name
[
argument ...
]
DESCRIPTION
is a command interpreter intended for both interactive and shell
script use.
Its command language is a superset of the
shC
shell language and largely compatible to the original Korn shell.
I'm an Android user, so what's mksh?
mksh
is a
UNIX
shell / command interpreter, similar to
COMMAND.COM
or
CMD.EXE
which has been included with
Android Open Source Project
for a while now.
Basically, it's a program that runs in a terminal (console window),
takes user input and runs commands or scripts, which it can also
be asked to do by other programs, even in the background.
Any privilege pop-ups you might be encountering are thus not
mksh
issues but questions by some other program utilising it.
Invocation
Most builtins can be called directly, for example if a link points from its
name to the shell; not all make sense, have been tested or work at all though.
The options are as follows:
- -c string
-
will execute the command(s) contained in
string
- -i
-
Interactive shell.
A shell that reads commands from standard input is
``interactive''
if this
option is used or if both standard input and standard error are attached
to a
tty(4).
An interactive shell has job control enabled, ignores the
SIGINT
SIGQUIT
and
SIGTERM
signals, and prints prompts before reading input (see the
PS1
and
PS2
parameters).
It also processes the
ENV
parameter or the
mkshrc
file (see below).
For non-interactive shells, the
trackall
option is on by default (see the
set
command below).
- -l
-
Login shell.
If the basename the shell is called with (i.e. argv[0])
starts with
`-'
or if this option is used,
the shell is assumed to be a login shell; see
Sx Startup files
below.
- -p
-
Privileged shell.
A shell is
``privileged''
if the real user ID or group ID does not match the
effective user ID or group ID (see
getuid(2)
and
getgid(2)).
Clearing the privileged option causes the shell to set
its effective user ID (group ID) to its real user ID (group ID).
For further implications, see
Sx Startup files .
If the shell is privileged and this flag is not explicitly set, the
``privileged''
option is cleared automatically after processing the startup files.
- -r
-
Restricted shell.
A shell is
``restricted''
if this
option is used.
The following restrictions come into effect after the shell processes any
profile and
ENV
files:
-
The
cd
Po and Ic chdir Pc
command is disabled.
-
The
SHELL
ENV
and
PATH
parameters cannot be changed.
-
Command names can't be specified with absolute or relative paths.
-
The
-p
option of the built-in command
command
can't be used.
-
Redirections that create files can't be used (i.e.
`>'
`>|'
`>>'
`<>'
- -s
-
The shell reads commands from standard input; all non-option arguments
are positional parameters.
- -T name
-
Spawn
on the
tty(4)
device given.
The paths
name
/dev/ttyC name
and
/dev/tty name
are attempted in order.
Unless
name
begins with an exclamation mark
(`!'
)
this is done in a subshell and returns immediately.
If
name
is a dash
(`-'
)
detach from controlling terminal (daemonise) instead.
In addition to the above, the options described in the
set
built-in command can also be used on the command line:
both
[-+abCefhkmnuvXx and
]
[-+o option
]
can be used for single letter or long options, respectively.
If neither the
-c
nor the
-s
option is specified, the first non-option argument specifies the name
of a file the shell reads commands from.
If there are no non-option
arguments, the shell reads commands from the standard input.
The name of the shell (i.e. the contents of $0)
is determined as follows: if the
-c
option is used and there is a non-option argument, it is used as the name;
if commands are being read from a file, the file is used as the name;
otherwise, the basename the shell was called with (i.e. argv[0]) is used.
The exit status of the shell is 127 if the command file specified on the
command line could not be opened, or non-zero if a fatal syntax error
occurred during the execution of a script.
In the absence of fatal errors,
the exit status is that of the last command executed, or zero, if no
command is executed.
Startup files
For the actual location of these files, see
Sx FILES .
A login shell processes the system profile first.
A privileged shell then processes the suid profile.
A non-privileged login shell processes the user profile next.
A non-privileged interactive shell checks the value of the
ENV
parameter after subjecting it to parameter, command, arithmetic and tilde
(`~'
)
substitution; if unset or empty, the user mkshrc profile is processed;
otherwise, if a file whose name is the substitution result exists,
it is processed; non-existence is silently ignored.
A privileged shell then drops privileges if neither was the
-
p
option given on the command line nor set during execution of the startup files.
Command syntax
The shell begins parsing its input by removing any backslash-newline
combinations, then breaking it into
words
Words (which are sequences of characters) are delimited by unquoted whitespace
characters (space, tab, and newline) or meta-characters
Po `<'
`>'
`|'
`;'
,
`('
,
`)'
,
and
`&'
Pc .
Aside from delimiting words, spaces and tabs are ignored, while newlines
usually delimit commands.
The meta-characters are used in building the following
tokens
`<'
`<&'
,
`<<'
`<<<'
`>'
`>&'
,
`>>'
`&>'
etc. are used to specify redirections (see
Sx Input/output redirection
below);
`|'
is
used to create pipelines;
`|&'
is used to create co-processes (see
Sx Co-processes
below);
`;'
is used to separate commands;
`&'
is used to create asynchronous pipelines;
`&&'
and
`||'
are
used to specify conditional execution;
`;;'
,
`;&'
and
`;|'
are used in
case
statements;
`(('
is used in arithmetic expressions;
and lastly,
`('
is used to create subshells.
Whitespace and meta-characters can be quoted individually using a backslash
(`\'
)
or in groups using double
(`'
)
or single
(`''
)
quotes.
Note that the following characters are also treated specially by the
shell and must be quoted if they are to represent themselves:
`\'
,
`'
,
`''
,
`#'
,
`$'
,
``'
,
`~'
,
`{'
,
`}'
,
`*'
,
`?'
,
and
`['
The first three of these are the above mentioned quoting characters (see
Sx Quoting
below);
`#'
,
if used at the beginning of a word, introduces a comment --- everything after
the
`#'
up to the nearest newline is ignored;
`$'
is used to introduce parameter, command, and arithmetic substitutions (see
Sx Substitution
below);
``'
introduces an old-style command substitution (see
Sx Substitution
below);
`~'
begins a directory expansion (see
Sx Tilde expansion
below);
`{'
and
`}'
delimit
csh(1)Ns-style
alterations (see
Sx Brace expansion
below);
and finally,
`*'
,
`?'
,
and
`['
are used in file name generation (see
Sx File name patterns
below).
As words and tokens are parsed, the shell builds commands, of which there
are two basic types:
simple-commands
typically programmes that are executed, and
compound-commands
such as
for
and
if
statements, grouping constructs, and function definitions.
A simple-command consists of some combination of parameter assignments
(see
Sx Parameters
below),
input/output redirections (see
Sx Input/output redirections
below),
and command words; the only restriction is that parameter assignments come
before any command words.
The command words, if any, define the command
that is to be executed and its arguments.
The command may be a shell built-in command, a function,
or an external command
(i.e. a separate executable file that is located using the
PATH
parameter; see
Sx Command execution
below).
Note that all command constructs have an exit status: for external commands,
this is related to the status returned by
wait(2)
(if the command could not be found, the exit status is 127; if it could not
be executed, the exit status is 126); the exit status of other command
constructs (built-in commands, functions, compound-commands, pipelines, lists,
etc.) are all well-defined and are described where the construct is
described.
The exit status of a command consisting only of parameter
assignments is that of the last command substitution performed during the
parameter assignment or 0 if there were no command substitutions.
Commands can be chained together using the
`|'
token
to form pipelines, in which the standard output of each command but the
last is piped (see
pipe(2))
to the standard input of the following command.
The exit status of a pipeline is that of its last command, unless the
pipefail
option is set (see there).
All commands of a pipeline are executed in separate subshells;
this is allowed by POSIX but differs from both variants of
AT&T System
ksh
where all but the last command were executed in subshells; see the
read
builtin's description for implications and workarounds.
A pipeline may be prefixed by the
`!'
reserved word which causes the exit status of the pipeline to be logically
complemented: if the original status was 0, the complemented status will be 1;
if the original status was not 0, the complemented status will be 0.
Lists
of commands can be created by separating pipelines by any of the following
tokens:
`&&'
,
`||'
`&'
,
`|&'
,
and
`;'
The first two are for conditional execution:
``cmd1 && cmd2
''
executes
cmd2
only if the exit status of
cmd1
is zero;
`||'
is
the opposite ---
cmd2
is executed only if the exit status of
cmd1
is non-zero.
`&&'
and
`||'
have
equal precedence which is higher than that of
`&'
,
`|&'
,
and
`;'
,
which also have equal precedence.
Note that the
`&&'
and
`||'
operators
are
Qq left-associative .
For example, both of these commands will print only
Qq bar :
$ false && echo foo || echo bar
$ true || echo foo && echo bar
The
`&'
token causes the preceding command to be executed asynchronously; that is,
the shell starts the command but does not wait for it to complete (the shell
does keep track of the status of asynchronous commands; see
Sx Job control
below).
When an asynchronous command is started when job control is disabled
(i.e. in most scripts), the command is started with signals
SIGINT
and
SIGQUIT
ignored and with input redirected from
/dev/null
(however, redirections specified in the asynchronous command have precedence).
The
`|&'
operator starts a co-process which is a special kind of asynchronous process
(see
Sx Co-processes
below).
Note that a command must follow the
`&&'
and
`||'
operators,
while it need not follow
`&'
,
`|&'
,
or
`;'
The exit status of a list is that of the last command executed, with the
exception of asynchronous lists, for which the exit status is 0.
Compound commands are created using the following reserved words.
These words
are only recognised if they are unquoted and if they are used as the first
word of a command (i.e. they can't be preceded by parameter assignments or
redirections):
case else function then ! (
do esac if time [[ ((
done fi in until {
elif for select while }
In the following compound command descriptions, command lists (denoted as
list
that are followed by reserved words must end with a semicolon, a newline, or
a (syntactically correct) reserved word.
For example, the following are all valid:
$ { echo foo; echo bar; }
$ { echo foo; echo bar<newline>}
$ { { echo foo; echo bar; } }
This is not valid:
$ { echo foo; echo bar
- (list
)
-
Execute
list
in a subshell.
There is no implicit way to pass environment changes from a
subshell back to its parent.
- { list ; }
-
Compound construct;
list
is executed, but not in a subshell.
Note that
`{'
and
`}'
are reserved words, not meta-characters.
-
case word in
[[(]
pattern
[| pat
]
... )
list
[;; | ;& | ;| ]
... esac]
-
- The
case
statement attempts to match
word
against a specified
pattern
the
list
associated with the first successfully matched pattern is executed.
Patterns used in
case
statements are the same as those used for file name patterns except that the
restrictions regarding
`.'
and
`/'
are dropped.
Note that any unquoted space before and after a pattern is
stripped; any space within a pattern must be quoted.
Both the word and the
patterns are subject to parameter, command, and arithmetic substitution, as
well as tilde substitution.
For historical reasons, open and close braces may be used instead of
in
and
esac
e.g.
case $foo { *) echo bar;; }
The list terminators are:
- `;;'
-
Terminate after the list.
- `;&'
-
Fall through into the next list.
- `;|'
-
Evaluate the remaining pattern-list tuples.
The exit status of a
case
statement is that of the executed
list
if no
list
is executed, the exit status is zero.
-
for name
[in word ... ]
do list ; done
-
- For each
word
in the specified word list, the parameter
name
is set to the word and
list
is executed.
If
in
is not used to specify a word list, the positional parameters
($1, $2, etc.)
are used instead.
For historical reasons, open and close braces may be used instead of
do
and
done
e.g.
for i; { echo $i; }
The exit status of a
for
statement is the last exit status of
list
if
list
is never executed, the exit status is zero.
-
if list
then list
[elif list
then list ; ]
...
[else list ; ]
fi
-
- If the exit status of the first
list
is zero, the second
list
is executed; otherwise, the
list
following the
elif
if any, is executed with similar consequences.
If all the lists following the
if
and
elif s
fail (i.e. exit with non-zero status), the
list
following the
else
is executed.
The exit status of an
if
statement is that of non-conditional
list
that is executed; if no non-conditional
list
is executed, the exit status is zero.
-
select name
[in word ... ]
do list ; done
-
- The
select
statement provides an automatic method of presenting the user with a menu and
selecting from it.
An enumerated list of the specified
word (s)
is printed on standard error, followed by a prompt
Po PS3: normally
`#? '
Pc .
A number corresponding to one of the enumerated words is then read from
standard input,
name
is set to the selected word (or unset if the selection is not valid),
REPLY
is set to what was read (leading/trailing space is stripped), and
list
is executed.
If a blank line (i.e. zero or more
IFS
octets) is entered, the menu is reprinted without executing
list
When
list
completes, the enumerated list is printed if
REPLY
is
NULL
the prompt is printed, and so on.
This process continues until an end-of-file
is read, an interrupt is received, or a
break
statement is executed inside the loop.
If
``in word ...''
is omitted, the positional parameters are used
(i.e. $1, $2, etc.).
For historical reasons, open and close braces may be used instead of
do
and
done
e.g.
select i; { echo $i; }
The exit status of a
select
statement is zero if a
break
statement is used to exit the loop, non-zero otherwise.
-
until list
do list
done
-
- This works like
while
except that the body is executed only while the exit status of the first
list
is non-zero.
-
while list
do list
done
-
- A
while
is a pre-checked loop.
Its body is executed as often as the exit status of the first
list
is zero.
The exit status of a
while
statement is the last exit status of the
list
in the body of the loop; if the body is not executed, the exit status is zero.
-
function name
{ list ; }
-
- Defines the function
name
(see
Sx Functions
below).
Note that redirections specified after a function definition are
performed whenever the function is executed, not when the function definition
is executed.
- name () command
-
Mostly the same as
function
(see
Sx Functions
below).
Whitespace (space or tab) after
name
will be ignored most of the time.
-
function name ()
{ list ; }
-
- The same as
name ()
(bash ism
)
The
function
keyword is ignored.
-
time [-p
]
[pipeline
]
-
- The
Sx Command execution
section describes the
time
reserved word.
- (( expression ))
-
The arithmetic expression
expression
is evaluated; equivalent to
``let expression''
(see
Sx Arithmetic expressions
and the
let
command, below).
- Bq Bq expression
-
Similar to the
test
and
[ ... ]
commands (described later), with the following exceptions:
-
Field splitting and file name generation are not performed on arguments.
-
The
-a
(AND)
and
-o
(OR)
operators are replaced with
`&&'
and
`||'
respectively.
-
Operators (e.g.
`-f
'
`='
`!'
must be unquoted.
-
Parameter, command, and arithmetic substitutions are performed as expressions
are evaluated and lazy expression evaluation is used for the
`&&'
and
`||'
operators.
This means that in the following statement,
$(<foo)
is evaluated if and only if the file
foo
exists and is readable:
$ [[ -r foo && $(<foo) = b*r ]]
-
The second operand of the
`!='
and
`='
expressions are a subset of patterns (e.g. the comparison
[[ foobar = f*r ]]
succeeds).
This even works indirectly:
$ bar=foobar; baz='f*r'
$ [[ $bar = $baz ]]; echo $?
$ [[ $bar = "$baz" ]]; echo $?
Perhaps surprisingly, the first comparison succeeds,
whereas the second doesn't.
This does not apply to all extglob metacharacters, currently.
Quoting
Quoting is used to prevent the shell from treating characters or words
specially.
There are three methods of quoting.
First,
`\'
quotes the following character, unless it is at the end of a line, in which
case both the
`\'
and the newline are stripped.
Second, a single quote
(`''
)
quotes everything up to the next single quote (this may span lines).
Third, a double quote
(`'
)
quotes all characters, except
`$'
,
``'
and
`\'
,
up to the next unquoted double quote.
`$'
and
``'
inside double quotes have their usual meaning (i.e. parameter, command, or
arithmetic substitution) except no field splitting is carried out on the
results of double-quoted substitutions.
If a
`\'
inside a double-quoted string is followed by
`\'
,
`$'
,
``'
,
or
`'
,
it is replaced by the second character; if it is followed by a newline, both
the
`\'
and the newline are stripped; otherwise, both the
`\'
and the character following are unchanged.
If a single-quoted string is preceded by an unquoted
`$'
,
C style backslash expansion (see below) is applied (even single quote
characters inside can be escaped and do not terminate the string then);
the expanded result is treated as any other single-quoted string.
If a double-quoted string is preceded by an unquoted
`$'
,
the latter is ignored.
Backslash expansion
In places where backslashes are expanded, certain C and
AT&T System
ksh
or GNU
bash
style escapes are translated.
These include
`\a'
,
`\b'
,
`\f'
,
`\n'
,
`\r'
,
`\t'
,
`\U########'
,
`\u####'
,
and
`\v'
For
`\U########'
and
`\u####'
,
``#''
means a hexadecimal digit, of thich there may be none up to four or eight;
these escapes translate a Unicode codepoint to UTF-8.
Furthermore,
`\E'
and
`\e'
expand to the escape character.
In the
print
builtin mode,
`\'
,
`\''
,
and
`\?'
are explicitly excluded;
octal sequences must have the none up to three octal digits
``#''
prefixed with the digit zero
(`\0###'
)
hexadecimal sequences
`\x##'
are limited to none up to two hexadecimal digits
``#''
both octal and hexadecimal sequences convert to raw octets;
`\#'
,
where # is none of the above, translates to \# (backslashes are retained).
Backslash expansion in the C style mode slightly differs: octal sequences
`\###'
must have no digit zero prefixing the one up to three octal digits
``#''
and yield raw octets; hexadecimal sequences
`\x#*'
greedily eat up as many hexadecimal digits
``#''
as they can and terminate with the first non-hexadecimal digit;
these translate a Unicode codepoint to UTF-8.
The sequence
`\c#'
,
where
``#''
is any octet, translates to Ctrl-# (which basically means,
`\c?'
becomes DEL, everything else is bitwise ANDed with 0x1F).
Finally,
`\#'
,
where # is none of the above, translates to # (has the backslash trimmed),
even if it is a newline.
Aliases
There are two types of aliases: normal command aliases and tracked aliases.
Command aliases are normally used as a short hand for a long or often used
command.
The shell expands command aliases (i.e. substitutes the alias name
for its value) when it reads the first word of a command.
An expanded alias is re-processed to check for more aliases.
If a command alias ends in a
space or tab, the following word is also checked for alias expansion.
The alias expansion process stops when a word that is not an alias is found,
when a quoted word is found, or when an alias word that is currently being
expanded is found.
Aliases are specifically an interactive feature: while they do happen
to work in scripts and on the command line in some cases, aliases are
expanded during lexing, so their use must be in a separate command tree
from their definition; otherwise, the alias will not be found.
Noticeably, command lists (separated by semicolon, in command substitutions
also by newline) may be one same parse tree.
The following command aliases are defined automatically by the shell:
autoload='typeset -fu'
functions='typeset -f'
hash='alias -t'
history='fc -l'
integer='typeset -i'
local='typeset'
login='exec login'
nameref='typeset -n'
nohup='nohup '
r='fc -e -'
stop='kill -STOP'
type='whence -v'
Tracked aliases allow the shell to remember where it found a particular
command.
The first time the shell does a path search for a command that is
marked as a tracked alias, it saves the full path of the command.
The next
time the command is executed, the shell checks the saved path to see that it
is still valid, and if so, avoids repeating the path search.
Tracked aliases can be listed and created using
alias -t
Note that changing the
PATH
parameter clears the saved paths for all tracked aliases.
If the
trackall
option is set (i.e.
set -o trackall
or
set -h )
the shell tracks all commands.
This option is set automatically for non-interactive shells.
For interactive shells, only the following commands are
automatically tracked:
cat(1),
cc(1),
chmod(1),
cp(1),
date(1),
ed(1),
emacs(1),
grep(1),
ls(1),
make(1),
mv(1),
pr(1),
rm(1),
sed(1),
sh(1),
vi(1),
and
who(1).
Substitution
The first step the shell takes in executing a simple-command is to perform
substitutions on the words of the command.
There are three kinds of
substitution: parameter, command, and arithmetic.
Parameter substitutions,
which are described in detail in the next section, take the form
$
name
or
${
... }
command substitutions take the form
$(
command )
or (deprecated)
`
command `
or (executed in the current environment)
${
command ;}
and strip trailing newlines;
and arithmetic substitutions take the form
$((
expression ))
Parsing the current-environment command substitution requires a space,
tab or newline after the opening brace and that the closing brace be
recognised as a keyword (i.e. is preceded by a newline or semicolon).
They are also called funsubs (function substitutions) and behave like
functions in that
local
and
return
work, and in that
exit
terminates the parent shell.
Another variant of substitution are the valsubs (value substitutions)
${| command ;}
which are also executed in the current environment, like funsubs, but
share their I/O with the parent; instead, they evaluate to whatever
the, initially empty, expression-local variable
REPLY
is set to within the
command s
If a substitution appears outside of double quotes, the results of the
substitution are generally subject to word or field splitting according to
the current value of the
IFS
parameter.
The
IFS
parameter specifies a list of octets which are used to break a string up
into several words; any octets from the set space, tab, and newline that
appear in the
IFS
octets are called
``IFS whitespace''
Sequences of one or more
IFS
whitespace octets, in combination with zero or one
non- IFS
whitespace octets, delimit a field.
As a special case, leading and trailing
IFS
whitespace is stripped (i.e. no leading or trailing empty field
is created by it); leading or trailing
non- IFS
whitespace does create an empty field.
Example: If
IFS
is set to
``<space>:''
and VAR is set to
``<space>A<space>:<space><space>B::D''
the substitution for $VAR results in four fields:
`A'
`B'
`(an empty field),'
and
`D'
Note that if the
IFS
parameter is set to the
NULL
string, no field splitting is done; if the parameter is unset, the default
value of space, tab, and newline is used.
Also, note that the field splitting applies only to the immediate result of
the substitution.
Using the previous example, the substitution for $VAR:E
results in the fields:
`A'
`B'
`,'
and
`D:E'
not
`A'
`B'
`,'
`D'
and
`E'
This behavior is POSIX compliant, but incompatible with some other shell
implementations which do field splitting on the word which contained the
substitution or use
IFS
as a general whitespace delimiter.
The results of substitution are, unless otherwise specified, also subject to
brace expansion and file name expansion (see the relevant sections below).
A command substitution is replaced by the output generated by the specified
command which is run in a subshell.
For
$( command )
and
${ command ;}
substitutions, normal quoting rules are used when
command
is parsed; however, for the deprecated
` command `
form, a
`\'
followed by any of
`$'
,
``'
,
or
`\'
is stripped (a
`\'
followed by any other character is unchanged).
As a special case in command substitutions, a command of the form
< file
is interpreted to mean substitute the contents of
file
Note that
$(<foo)
has the same effect as
$(cat foo)
Note that some shells do not use a recursive parser for command substitutions,
leading to failure for certain constructs; to be portable, use as workaround
`x=$(cat)'
<<EOF
(or the newline-keeping
`x=<<EOF'
extension) instead to merely slurp the string.
St -p1003.1
recommends to use case statements of the form
`x=$(case'
$foo in (bar) echo $bar ;; (*) echo $baz ;; esac)
instead, which would work but not serve as example for this portability issue.
x=$(case $foo in bar) echo $bar ;; *) echo $baz ;; esac)
# above fails to parse on old shells; below is the workaround
x=$(eval $(cat)) <<"EOF"
case $foo in bar) echo $bar ;; *) echo $baz ;; esac
EOF
Arithmetic substitutions are replaced by the value of the specified expression.
For example, the command
print $((2+3*4))
displays 14.
See
Sx Arithmetic expressions
for a description of an expression.
Parameters
Parameters are shell variables; they can be assigned values and their values
can be accessed using a parameter substitution.
A parameter name is either one
of the special single punctuation or digit character parameters described
below, or a letter followed by zero or more letters or digits
Po `_'
counts as a letter
Pc .
The latter form can be treated as arrays by appending an array index of the
form
[
expr
]
where
expr
is an arithmetic expression.
Array indices in
are limited to the range 0 through 4294967295, inclusive.
That is, they are a 32-bit unsigned integer.
Parameter substitutions take the form
$ name
${ name }
or
${ name [expr ]
where
name
is a parameter name.
Substitution of all array elements with
${ name [*]}
and
${ name [@]}
works equivalent to $* and $@ for positional parameters.
If substitution is performed on a parameter
(or an array parameter element)
that is not set, a null string is substituted unless the
nounset
option
Po set -o nounset
or
set -u
Pc is set, in which case an error occurs.
Parameters can be assigned values in a number of ways.
First, the shell implicitly sets some parameters like
`#'
,
`PWD'
,
and
`$'
;
this is the only way the special single character parameters are set.
Second, parameters are imported from the shell's environment at startup.
Third, parameters can be assigned values on the command line: for example,
FOO=bar
sets the parameter
``FOO''
to
``bar''
multiple parameter assignments can be given on a single command line and they
can be followed by a simple-command, in which case the assignments are in
effect only for the duration of the command (such assignments are also
exported; see below for the implications of this).
Note that both the parameter name and the
`='
must be unquoted for the shell to recognise a parameter assignment.
The construct
FOO+=baz
is also recognised; the old and new values are immediately concatenated.
The fourth way of setting a parameter is with the
export
global
readonly
and
typeset
commands; see their descriptions in the
Sx Command execution
section.
Fifth,
for
and
select
loops set parameters as well as the
getopts
read
and
set -A
commands.
Lastly, parameters can be assigned values using assignment operators
inside arithmetic expressions (see
Sx Arithmetic expressions
below) or using the
${ name = value }
form of the parameter substitution (see below).
Parameters with the export attribute (set using the
export
or
typeset -x
commands, or by parameter assignments followed by simple commands) are put in
the environment (see
environ(7))
of commands run by the shell as
name = value
pairs.
The order in which parameters appear in the environment of a command is
unspecified.
When the shell starts up, it extracts parameters and their values
from its environment and automatically sets the export attribute for those
parameters.
Modifiers can be applied to the
${ name }
form of parameter substitution:
- ${ name :- word }
-
If
name
is set and not
NULL
it is substituted; otherwise,
word
is substituted.
- ${ name :+ word }
-
If
name
is set and not
NULL
word
is substituted; otherwise, nothing is substituted.
- ${ name := word }
-
If
name
is set and not
NULL
it is substituted; otherwise, it is assigned
word
and the resulting value of
name
is substituted.
- ${ name :? word }
-
If
name
is set and not
NULL
it is substituted; otherwise,
word
is printed on standard error (preceded by
name :
and an error occurs (normally causing termination of a shell script, function,
or script sourced using the
`.'
built-in).
If
word
is omitted, the string
``parameter null or not set''
is used instead.
Currently a bug, if
word
is a variable which expands to the null string, the
error message is also printed.
Note that, for all of the above,
word
is actually considered quoted, and special parsing rules apply.
The parsing rules also differ on whether the expression is double-quoted:
word
then uses double-quoting rules, except for the double quote itself
(`'
)
and the closing brace, which, if backslash escaped, gets quote removal applied.
In the above modifiers, the
`:'
can be omitted, in which case the conditions only depend on
name
being set (as opposed to set and not
NULL )
If
word
is needed, parameter, command, arithmetic, and tilde substitution are performed
on it; if
word
is not needed, it is not evaluated.
The following forms of parameter substitution can also be used (if
name
is an array, its element #0 will be substituted in a scalar context):
- ${# name }
-
The number of positional parameters if
name
is
`*'
,
`@'
,
or not specified; otherwise the length
(in characters)
of the string value of parameter
name
- ${# name [*]}
-
- ${# name [@]}
-
The number of elements in the array
name
- ${% name }
-
The width
(in screen columns)
of the string value of parameter
name
or -1 if
${ name }
contains a control character.
- ${! name }
-
The name of the variable referred to by
name
This will be
name
except when
name
is a name reference (bound variable), created by the
nameref
command (which is an alias for
typeset -n
- ${! name [*]}
-
- ${! name [@]}
-
The names of indices (keys) in the array
name
-
${ name
# pattern }
-
-
${ name
## pattern }
-
- If
pattern
matches the beginning of the value of parameter
name
the matched text is deleted from the result of substitution.
A single
`#'
results in the shortest match, and two
of them result in the longest match.
Cannot be applied to a vector
(${*} or ${@} or ${array[*]} or ${array[@]})
-
${ name
% pattern }
-
-
${ name
%% pattern }
-
- Like ${..#..} substitution, but it deletes from the end of the value.
Cannot be applied to a vector.
-
${ name
/ pattern / string }
-
-
${ name
// pattern / string }
-
- Like ${..#..} substitution, but it replaces the longest match of
pattern
anchored anywhere in the value, with
string
If
pattern
begins with
`#'
,
it is anchored at the beginning of the value; if it begins with
`%'
,
it is anchored at the end.
Patterns that are empty or consist only of wildcards are invalid.
A single
`/'
replaces the first occurence of the search
pattern
and two of them replace all occurences.
If
/ string
is omitted, the
pattern
is replaced by the empty string, i.e. deleted.
Cannot be applied to a vector.
Inefficiently implemented, may be slow.
-
${ name : pos
: len }
-
- The first
len
characters of
name
starting at position
pos
are substituted.
Both
pos
and
: len
are optional.
If
pos
is negative, counting starts at the end of the string; if it
is omitted, it defaults to 0.
If
len
is omitted or greater than the length of the remaining string,
all of it is substituted.
Both
pos
and
len
are evaluated as arithmetic expressions.
Currently,
pos
must start with a space, opening parenthesis or digit to be recognised.
Cannot be applied to a vector.
- ${ name @#}
-
The hash (using the BAFH algorithm) of the expansion of
name
This is also used internally for the shell's hashtables.
- ${ name @Q}
-
A quoted expression safe for re-entry, whose value is the value of the
name
parameter, is substituted.
Note that
pattern
may need extended globbing pattern
(@(...))
single
('...')
or double
(...)
quote escaping unless
-o sh
is set.
The following special parameters are implicitly set by the shell and cannot be
set directly using assignments:
- !
-
Process ID of the last background process started.
If no background processes have been started, the parameter is not set.
- #
-
The number of positional parameters ($1, $2, etc.).
- $
-
The PID of the shell, or the PID of the original shell if it is a subshell.
Do
NOT
use this mechanism for generating temporary file names; see
mktemp(1)
instead.
- -
-
The concatenation of the current single letter options (see the
set
command below for a list of options).
- ?
-
The exit status of the last non-asynchronous command executed.
If the last command was killed by a signal,
$?
is set to 128 plus the signal number.
- 0
-
The name of the shell, determined as follows:
the first argument to
if it was invoked with the
-c
option and arguments were given; otherwise the
file
argument, if it was supplied;
or else the basename the shell was invoked with (i.e.
argv[0] )
$0
is also set to the name of the current script or
the name of the current function, if it was defined with the
function
keyword (i.e. a Korn shell style function).
- 1 .. 9
-
The first nine positional parameters that were supplied to the shell, function,
or script sourced using the
`.'
built-in.
Further positional parameters may be accessed using
${ number }
- *
-
All positional parameters (except 0), i.e. $1, $2, $3, ...
If used
outside of double quotes, parameters are separate words (which are subjected
to word splitting); if used within double quotes, parameters are separated
by the first character of the
IFS
parameter (or the empty string if
IFS
is
NULL )
- @
-
Same as
$*
unless it is used inside double quotes, in which case a separate word is
generated for each positional parameter.
If there are no positional parameters, no word is generated.
$@
can be used to access arguments, verbatim, without losing
NULL
arguments or splitting arguments with spaces.
The following parameters are set and/or used by the shell:
- _
-
(underscore)
When an external command is executed by the shell, this parameter is set in the
environment of the new process to the path of the executed command.
In interactive use, this parameter is also set in the parent shell to the last
word of the previous command.
- BASHPID
-
The PID of the shell or subshell.
- CDPATH
-
Search path for the
cd
built-in command.
It works the same way as
PATH
for those directories not beginning with
`/'
in
cd
commands.
Note that if
CDPATH
is set and does not contain
`.'
or contains an empty path, the current directory is not searched.
Also, the
cd
built-in command will display the resulting directory when a match is found
in any search path other than the empty path.
- COLUMNS
-
Set to the number of columns on the terminal or window.
Always set, defaults to 80, unless the
value as reported by
stty(1)
is non-zero and sane enough (minimum is 12x3); similar for
LINES
This parameter is used by the interactive line editing modes, and by the
select
set -o
and
kill -l
commands to format information columns.
Importing from the environment or unsetting this parameter removes the
binding to the actual terminal size in favour of the provided value.
- ENV
-
If this parameter is found to be set after any profile files are executed, the
expanded value is used as a shell startup file.
It typically contains function and alias definitions.
- ERRNO
-
Integer value of the shell's
errno
variable.
It indicates the reason the last system call failed.
Not yet implemented.
- EXECSHELL
-
If set, this parameter is assumed to contain the shell that is to be used to
execute commands that
execve(2)
fails to execute and which do not start with a
``#! shell
''
sequence.
- FCEDIT
-
The editor used by the
fc
command (see below).
- FPATH
-
Like
PATH
but used when an undefined function is executed to locate the file defining the
function.
It is also searched when a command can't be found using
PATH
See
Sx Functions
below for more information.
- HISTFILE
-
The name of the file used to store command history.
When assigned to, history is loaded from the specified file.
Also, several invocations of the shell will share history if their
HISTFILE
parameters all point to the same file.
Note
If
HISTFILE
isn't set, no history file is used.
This is different from
AT&T System
ksh
- HISTSIZE
-
The number of commands normally stored for history.
The default is 2047.
Do not set this value to insanely high values such as 1000000000 because
can then not allocate enough memory for the history and will not start.
- HOME
-
The default directory for the
cd
command and the value substituted for an unqualified
~
(see
Sx Tilde expansion
below).
- IFS
-
Internal field separator, used during substitution and by the
read
command, to split values into distinct arguments; normally set to space, tab,
and newline.
See
Sx Substitution
above for details.
Note
This parameter is not imported from the environment when the shell is
started.
- KSHEGID
-
The effective group id of the shell.
- KSHGID
-
The real group id of the shell.
- KSHUID
-
The real user id of the shell.
- KSH_VERSION
-
The name and version of the shell (read-only).
See also the version commands in
Sx Emacs editing mode
and
Sx Vi editing mode
sections, below.
- LINENO
-
The line number of the function or shell script that is currently being
executed.
- LINES
-
Set to the number of lines on the terminal or window.
Always set, defaults to 24.
See
COLUMNS
- EPOCHREALTIME
-
Time since the epoch, as returned by
gettimeofday(2),
formatted as decimal
tv_sec
followed by a dot
(`.'
)
and
tv_usec
padded to exactly six decimal digits.
- OLDPWD
-
The previous working directory.
Unset if
cd
has not successfully changed directories since the shell started, or if the
shell doesn't know where it is.
- OPTARG
-
When using
getopts
it contains the argument for a parsed option, if it requires one.
- OPTIND
-
The index of the next argument to be processed when using
getopts
Assigning 1 to this parameter causes
getopts
to process arguments from the beginning the next time it is invoked.
- PATH
-
A colon separated list of directories that are searched when looking for
commands and files sourced using the
`.'
command (see below).
An empty string resulting from a leading or trailing
colon, or two adjacent colons, is treated as a
`.'
(the current directory).
- PGRP
-
The process ID of the shell's process group leader.
- PIPESTATUS
-
An array containing the errorlevel (exit status) codes,
one by one, of the last pipeline run in the foreground.
- PPID
-
The process ID of the shell's parent.
- PS1
-
The primary prompt for interactive shells.
Parameter, command, and arithmetic
substitutions are performed, and
`!'
is replaced with the current command number (see the
fc
command below).
A literal
`!'
can be put in the prompt by placing
`!!'
in
PS1
The default prompt is
`$ '
for non-root users,
`# '
for root.
If
is invoked by root and
PS1
does not contain a
`#'
character, the default value will be used even if
PS1
already exists in the environment.
The
distribution comes with a sample
dot.mkshrc
containing a sophisticated example, but you might like the following one
(note that ${HOSTNAME:=$(hostname)} and the
root-vs-user distinguishing clause are (in this example) executed at
PS1
assignment time, while the $USER and $PWD are escaped
and thus will be evaluated each time a prompt is displayed):
PS1='${USER:=$(id -un)}'"@${HOSTNAME:=$(hostname)}:\$PWD $(
if (( USER_ID )); then print \$; else print \#; fi) "
Note that since the command-line editors try to figure out how long the prompt
is (so they know how far it is to the edge of the screen), escape codes in
the prompt tend to mess things up.
You can tell the shell not to count certain
sequences (such as escape codes) by prefixing your prompt with a
character (such as Ctrl-A) followed by a carriage return and then delimiting
the escape codes with this character.
Any occurences of that character in the prompt are not printed.
By the way, don't blame me for
this hack; it's derived from the original
ksh88(1),
which did print the delimiter character so you were out of luck
if you did not have any non-printing characters.
Since Backslashes and other special characters may be
interpreted by the shell, to set
PS1
either escape the backslash itself,
or use double quotes.
The latter is more practical.
This is a more complex example,
avoiding to directly enter special characters (for example with
^V
in the emacs editing mode),
which embeds the current working directory,
in reverse video
(colour would work, too)
in the prompt string:
x=$(print \\001)
PS1="$x$(print \\r)$x$(tput so)$x\$PWD$x$(tput se)$x> "
Due to a strong suggestion from David G. Korn,
now also supports the following form:
PS1=$'\1\r\1\e[7m\1$PWD\1\e[0m\1> '
- PS2
-
Secondary prompt string, by default
`> '
used when more input is needed to complete a command.
- PS3
-
Prompt used by the
select
statement when reading a menu selection.
The default is
`#? '
- PS4
-
Used to prefix commands that are printed during execution tracing (see the
set -x
command below).
Parameter, command, and arithmetic substitutions are performed
before it is printed.
The default is
`+ '
You may want to set it to
`[$EPOCHREALTIME] '
instead, to include timestamps.
- PWD
-
The current working directory.
May be unset or
NULL
if the shell doesn't know where it is.
- RANDOM
-
Each time
RANDOM
is referenced, it is assigned a number between 0 and 32767 from
a Linear Congruential PRNG first.
- REPLY
-
Default parameter for the
read
command if no names are given.
Also used in
select
loops to store the value that is read from standard input.
- SECONDS
-
The number of seconds since the shell started or, if the parameter has been
assigned an integer value, the number of seconds since the assignment plus the
value that was assigned.
- TMOUT
-
If set to a positive integer in an interactive shell, it specifies the maximum
number of seconds the shell will wait for input after printing the primary
prompt
(PS1
)
If the time is exceeded, the shell exits.
- TMPDIR
-
The directory temporary shell files are created in.
If this parameter is not
set, or does not contain the absolute path of a writable directory, temporary
files are created in
/tmp
- USER_ID
-
The effective user id of the shell.
Tilde expansion
Tilde expansion which is done in parallel with parameter substitution, is done
on words starting with an unquoted
`~'
The characters following the tilde, up to the first
`/'
,
if any, are assumed to be a login name.
If the login name is empty,
`+'
,
or
`-'
,
the value of the
HOME
PWD
or
OLDPWD
parameter is substituted, respectively.
Otherwise, the password file is
searched for the login name, and the tilde expression is substituted with the
user's home directory.
If the login name is not found in the password file or
if any quoting or parameter substitution occurs in the login name, no
substitution is performed.
In parameter assignments
(such as those preceding a simple-command or those occurring
in the arguments of
alias
export
global
readonly
and
typeset )
tilde expansion is done after any assignment
(i.e. after the equals sign)
or after an unquoted colon
(`:'
)
login names are also delimited by colons.
The home directory of previously expanded login names are cached and re-used.
The
alias -d
command may be used to list, change, and add to this cache (e.g.
alias -d fac=/usr/local/facilities; cd ~fac/bin )
Brace expansion (alteration)
Brace expressions take the following form:
prefix { str1 ,...,
strN } suffix
The expressions are expanded to
N
words, each of which is the concatenation of
prefix
str i
and
suffix
(e.g.
``a{c,b{X,Y},d}e''
expands to four words:
``ace''
``abXe ,
''
``abYe ,
''
and
``ade )''
As noted in the example, brace expressions can be nested and the resulting
words are not sorted.
Brace expressions must contain an unquoted comma
(`,'
)
for expansion to occur (e.g.
{}
and
{foo}
are not expanded).
Brace expansion is carried out after parameter substitution
and before file name generation.
File name patterns
A file name pattern is a word containing one or more unquoted
`?'
,
`*'
,
`+'
,
`@'
,
or
`!'
characters or
``[..]''
sequences.
Once brace expansion has been performed, the shell replaces file
name patterns with the sorted names of all the files that match the pattern
(if no files match, the word is left unchanged).
The pattern elements have the following meaning:
- ?
-
Matches any single character.
- *
-
Matches any sequence of octets.
- [..]
-
Matches any of the octets inside the brackets.
Ranges of octets can be specified by separating two octets by a
`-'
(e.g.
``[a0-9]''
matches the letter
`a'
or any digit).
In order to represent itself, a
`-'
must either be quoted or the first or last octet in the octet list.
Similarly, a
`]'
must be quoted or the first octet in the list if it is to represent itself
instead of the end of the list.
Also, a
`!'
appearing at the start of the list has special meaning (see below), so to
represent itself it must be quoted or appear later in the list.
- [!..]
-
Like [..],
except it matches any octet not inside the brackets.
- *( pattern| ...| pattern
-
Matches any string of octets that matches zero or more occurrences of the
specified patterns.
Example: The pattern
*(foo|bar)
matches the strings
``,''
``foo''
``bar''
``foobarfoo''
etc.
- +( pattern| ...| pattern
-
Matches any string of octets that matches one or more occurrences of the
specified patterns.
Example: The pattern
+(foo|bar)
matches the strings
``foo''
``bar''
``foobar''
etc.
- ?( pattern| ...| pattern
-
Matches the empty string or a string that matches one of the specified
patterns.
Example: The pattern
?(foo|bar)
only matches the strings
``,''
``foo''
and
``bar''
- @( pattern| ...| pattern
-
Matches a string that matches one of the specified patterns.
Example: The pattern
@(foo|bar)
only matches the strings
``foo''
and
``bar''
- !( pattern| ...| pattern
-
Matches any string that does not match one of the specified patterns.
Examples: The pattern
!(foo|bar)
matches all strings except
``foo''
and
``bar''
the pattern
!(*)
matches no strings; the pattern
!(?)*
matches all strings (think about it).
Note that complicated globbing, especially with alternatives,
is slow; using separate comparisons may (or may not) be faster.
Note that
mksh
Po and Nm pdksh Pc
never matches
`.'
and
`..'
but
AT&T System
ksh
Bourne
sh
and GNU
bash
do.
Note that none of the above pattern elements match either a period
(`.'
)
at the start of a file name or a slash
(`/'
)
even if they are explicitly used in a [..] sequence; also, the names
`.'
and
`..'
are never matched, even by the pattern
`.*'
If the
markdirs
option is set, any directories that result from file name generation are marked
with a trailing
`/'
Input/output redirection
When a command is executed, its standard input, standard output, and standard
error (file descriptors 0, 1, and 2, respectively) are normally inherited from
the shell.
Three exceptions to this are commands in pipelines, for which
standard input and/or standard output are those set up by the pipeline,
asynchronous commands created when job control is disabled, for which standard
input is initially set to be from
/dev/null
and commands for which any of the following redirections have been specified:
- > file
-
Standard output is redirected to
file
If
file
does not exist, it is created; if it does exist, is a regular file, and the
noclobber
option is set, an error occurs; otherwise, the file is truncated.
Note that this means the command
cmd <foo >foo
will open
foo
for reading and then truncate it when it opens it for writing, before
cmd
gets a chance to actually read
foo
- >| file
-
Same as
>
except the file is truncated, even if the
noclobber
option is set.
- >> file
-
Same as
>
except if
file
exists it is appended to instead of being truncated.
Also, the file is opened
in append mode, so writes always go to the end of the file (see
open(2)).
- < file
-
Standard input is redirected from
file
which is opened for reading.
- <> file
-
Same as
<
except the file is opened for reading and writing.
- << marker
-
After reading the command line containing this kind of redirection (called a
``here document )''
the shell copies lines from the command source into a temporary file until a
line matching
marker
is read.
When the command is executed, standard input is redirected from the
temporary file.
If
marker
contains no quoted characters, the contents of the temporary file are processed
as if enclosed in double quotes each time the command is executed, so
parameter, command, and arithmetic substitutions are performed, along with
backslash
(`\'
)
escapes for
`$'
,
``'
,
`\'
,
and
`\newline'
,
but not for
`'
If multiple here documents are used on the same command line, they are saved in
order.
If no
marker
is given, the here document ends at the next
<<
and substitution will be performed.
If
marker
is only a set of either single
``''''
or double
`'
quotes with nothing in between, the here document ends at the next empty line
and substitution will not be performed.
- <<- marker
-
Same as
<<
except leading tabs are stripped from lines in the here document.
- <<< word
-
Same as
<<
except that
word
is
the here document.
This is called a here string.
- <& fd
-
Standard input is duplicated from file descriptor
fd
fd
can be a number, indicating the number of an existing file descriptor;
the letter
`p'
,
indicating the file descriptor associated with the output of the current
co-process; or the character
`-'
,
indicating standard input is to be closed.
Note that
fd
is limited to a single digit in most shell implementations.
- >& fd
-
Same as
<&
except the operation is done on standard output.
- &> file
-
Same as
> file 2>&1
This is a GNU
bash
extension supported by
which also supports the preceding explicit fd number, for example,
3&> file
is the same as
3> file 2>&3
in
but a syntax error in GNU
bash
Setting the
-o posix
or
-o sh
shell options disable parsing of this redirection;
it's a compatibility feature to legacy scripts, to
not be used when writing new shell code.
-
&>| file
&>> file
&>& fd
-
- Same as
>| file
>> file
or
>& fd
followed by
2>&1
as above.
These are
extensions.
In any of the above redirections, the file descriptor that is redirected
(i.e. standard input or standard output)
can be explicitly given by preceding the
redirection with a number (portably, only a single digit).
Parameter, command, and arithmetic
substitutions, tilde substitutions, and (if the shell is interactive)
file name generation are all performed on the
file
marker
and
fd
arguments of redirections.
Note, however, that the results of any file name
generation are only used if a single file is matched; if multiple files match,
the word with the expanded file name generation characters is used.
Note
that in restricted shells, redirections which can create files cannot be used.
For simple-commands, redirections may appear anywhere in the command; for
compound-commands
Po if
statements, etc.
Pc ,
any redirections must appear at the end.
Redirections are processed after
pipelines are created and in the order they are given, so the following
will print an error with a line number prepended to it:
File descriptors created by input/output redirections are private to the
Korn shell, but passed to sub-processes if
-o posix
or
-o sh
is set.
Arithmetic expressions
Integer arithmetic expressions can be used with the
let
command, inside $((..)) expressions, inside array references (e.g.
name Bq expr
as numeric arguments to the
test
command, and as the value of an assignment to an integer parameter.
Warning
This also affects implicit conversion to integer, for example as done by the
let
command.
Never
use unchecked user input, e.g. from the environment, in arithmetics!
Expressions are calculated using signed arithmetic and the
Vt mksh_ari_t
type (a 32-bit signed integer), unless they begin with a sole
`#'
character, in which case they use
Vt mksh_uari_t
Po a 32-bit unsigned integer Pc .
Expressions may contain alpha-numeric parameter identifiers, array references,
and integer constants and may be combined with the following C operators
(listed and grouped in increasing order of precedence):
Unary operators:
+ - ! ~ ++ --
Binary operators:
,
= += -= *= /= %= <<<= >>>= <<= >>= &= ^= |=
||
&&
|
^
&
== !=
< <= > >=
<<< >>> << >>
+ -
* / %
Ternary operators:
?: (precedence is immediately higher than assignment)
Grouping operators:
( )
Integer constants and expressions are calculated using an exactly 32-bit
wide, signed or unsigned, type with silent wraparound on integer overflow.
Integer constants may be specified with arbitrary bases using the notation
base # number
where
base
is a decimal integer specifying the base, and
number
is a number in the specified base.
Additionally, base-16 integers may be specified by prefixing them with
`0x'
(case-insensitive)
in all forms of arithmetic expressions, except as numeric arguments to the
test
built-in command.
Prefixing numbers with a sole digit zero
(`0'
)
leads to the shell interpreting it as base-8 (octal) integer in
posix
mode
only
historically, (pd)ksh has never done so either anyway,
and it's unsafe to do that, but POSIX demands it nowadays.
As a special
mksh
extension, numbers to the base of one are treated as either (8-bit
transparent) ASCII or Unicode codepoints, depending on the shell's
utf8-mode
flag (current setting).
The
AT&T System
ksh93
syntax of
``'x'''
instead of
``1#x''
is also supported.
Note that NUL bytes (integral value of zero) cannot be used.
An unset or empty parameter evaluates to 0 in integer context.
In Unicode mode, raw octets are mapped into the range EF80..EFFF as in
OPTU-8, which is in the PUA and has been assigned by CSUR for this use.
If more than one octet in ASCII mode, or a sequence of more than one
octet not forming a valid and minimal CESU-8 sequence is passed, the
behaviour is undefined (usually, the shell aborts with a parse error,
but rarely, it succeeds, e.g. on the sequence C2 20).
That's why you should always use ASCII mode unless you know that the
input is well-formed UTF-8 in the range of 0000..FFFD.
The operators are evaluated as follows:
- unary
-
Result is the argument (included for completeness).
- unary -
-
Negation.
- !
-
Logical NOT;
the result is 1 if argument is zero, 0 if not.
- ~
-
Arithmetic (bit-wise) NOT.
- ++
-
Increment; must be applied to a parameter (not a literal or other expression).
The parameter is incremented by 1.
When used as a prefix operator, the result
is the incremented value of the parameter; when used as a postfix operator, the
result is the original value of the parameter.
- --
-
Similar to
++
except the parameter is decremented by 1.
- ,
-
Separates two arithmetic expressions; the left-hand side is evaluated first,
then the right.
The result is the value of the expression on the right-hand side.
- =
-
Assignment; the variable on the left is set to the value on the right.
-
+= -= *= /= %= <<<= >>>=
<<= >>= &= ^= |=
-
- Assignment operators.
Ao Ar var Ac Xo
Aq Ar op
= Aq expr
is the same as
Ao Ar var Ac Xo
= Aq var
Aq Ar op
Aq Ar expr ,
with any operator precedence in
Aq Ar expr
preserved.
For example,
``var1 *= 5 + 3''
is the same as specifying
``var1 = var1 * (5 + 3)''
- ||
-
Logical OR;
the result is 1 if either argument is non-zero, 0 if not.
The right argument is evaluated only if the left argument is zero.
- &&
-
Logical AND;
the result is 1 if both arguments are non-zero, 0 if not.
The right argument is evaluated only if the left argument is non-zero.
- |
-
Arithmetic (bit-wise) OR.
- ^
-
Arithmetic (bit-wise) XOR
(exclusive-OR).
- &
-
Arithmetic (bit-wise) AND.
- ==
-
Equal; the result is 1 if both arguments are equal, 0 if not.
- !=
-
Not equal; the result is 0 if both arguments are equal, 1 if not.
- <
-
Less than; the result is 1 if the left argument is less than the right, 0 if
not.
- <= > >=
-
Less than or equal, greater than, greater than or equal.
See
<
- <<< >>>
-
Rotate left (right); the result is similar to shift (see
<<
except that the bits shifted out at one end are shifted in
at the other end, instead of zero or sign bits.
- << >>
-
Shift left (right); the result is the left argument with its bits shifted left
(right) by the amount given in the right argument.
- + - *
-
Addition, subtraction, multiplication, and division.
- %
-
Remainder; the result is the symmetric remainder of the division of the left
argument by the right.
To get the mathematical modulus of
``a mod b
''
use the formula
Do (a % b + b)
% b
Dc .
-
Aq Ar arg1 ?
Aq Ar arg2 :
Aq Ar arg3
-
- If
Aq Ar arg1
is non-zero, the result is
Aq Ar arg2 ;
otherwise the result is
Aq Ar arg3 .
The non-result argument is not evaluated.
Co-processes
A co-process (which is a pipeline created with the
`|&'
operator) is an asynchronous process that the shell can both write to (using
print -p
and read from (using
read -p )
The input and output of the co-process can also be manipulated using
>&p
and
<&p
redirections, respectively.
Once a co-process has been started, another can't
be started until the co-process exits, or until the co-process's input has been
redirected using an
exec n >&p
redirection.
If a co-process's input is redirected in this way, the next
co-process to be started will share the output with the first co-process,
unless the output of the initial co-process has been redirected using an
exec n <&p
redirection.
Some notes concerning co-processes:
-
The only way to close the co-process's input (so the co-process reads an
end-of-file) is to redirect the input to a numbered file descriptor and then
close that file descriptor:
exec 3>&p; exec 3>&-
-
In order for co-processes to share a common output, the shell must keep the
write portion of the output pipe open.
This means that end-of-file will not be
detected until all co-processes sharing the co-process's output have exited
(when they all exit, the shell closes its copy of the pipe).
This can be
avoided by redirecting the output to a numbered file descriptor (as this also
causes the shell to close its copy).
Note that this behaviour is slightly
different from the original Korn shell which closes its copy of the write
portion of the co-process output when the most recently started co-process
(instead of when all sharing co-processes) exits.
-
print -p
will ignore
SIGPIPE
signals during writes if the signal is not being trapped or ignored; the same
is true if the co-process input has been duplicated to another file descriptor
and
print -u n
is used.
Functions
Functions are defined using either Korn shell
function function-name
syntax or the Bourne/POSIX shell
function-name ()
syntax (see below for the difference between the two forms).
Functions are like
.-scripts
(i.e. scripts sourced using the
`.'
built-in)
in that they are executed in the current environment.
However, unlike
.-scripts
shell arguments (i.e. positional parameters $1, $2, etc.)
are never visible inside them.
When the shell is determining the location of a command, functions
are searched after special built-in commands, before builtins and the
PATH
is searched.
An existing function may be deleted using
unset -f function-name
A list of functions can be obtained using
typeset +f
and the function definitions can be listed using
typeset -f
The
autoload
command (which is an alias for
typeset -fu
may be used to create undefined functions: when an undefined function is
executed, the shell searches the path specified in the
FPATH
parameter for a file with the same name as the function which, if found, is
read and executed.
If after executing the file the named function is found to
be defined, the function is executed; otherwise, the normal command search is
continued (i.e. the shell searches the regular built-in command table and
PATH )
Note that if a command is not found using
PATH
an attempt is made to autoload a function using
FPATH
(this is an undocumented feature of the original Korn shell).
Functions can have two attributes,
``trace''
and
``export''
which can be set with
typeset -ft
and
typeset -fx
respectively.
When a traced function is executed, the shell's
xtrace
option is turned on for the function's duration.
The
``export''
attribute of functions is currently not used.
In the original Korn shell,
exported functions are visible to shell scripts that are executed.
Since functions are executed in the current shell environment, parameter
assignments made inside functions are visible after the function completes.
If this is not the desired effect, the
typeset
command can be used inside a function to create a local parameter.
Note that
AT&T System
ksh93
uses static scoping (one global scope, one local scope per function)
and allows local variables only on Korn style functions, whereas
mksh
uses dynamic scoping (nested scopes of varying locality).
Note that special parameters (e.g.
$$ , $!
can't be scoped in this way.
The exit status of a function is that of the last command executed in the
function.
A function can be made to finish immediately using the
return
command; this may also be used to explicitly specify the exit status.
Functions defined with the
function
reserved word are treated differently in the following ways from functions
defined with the
()
notation:
-
The $0 parameter is set to the name of the function
(Bourne-style functions leave $0 untouched).
-
Parameter assignments preceding function calls are not kept in the shell
environment (executing Bourne-style functions will keep assignments).
-
OPTIND
is saved/reset and restored on entry and exit from the function so
getopts
can be used properly both inside and outside the function (Bourne-style
functions leave
OPTIND
untouched, so using
getopts
inside a function interferes with using
getopts
outside the function).
-
Bourne-style function definitions take precedence over alias dereferences
and remove alias definitions upon encounter, while aliases take precedence
over Korn-style functions.
In the future, the following differences may also be added:
-
A separate trap/signal environment will be used during the execution of
functions.
This will mean that traps set inside a function will not affect the
shell's traps and signals that are not ignored in the shell (but may be
trapped) will have their default effect in a function.
-
The EXIT trap, if set in a function, will be executed after the function
returns.
Command execution
After evaluation of command-line arguments, redirections, and parameter
assignments, the type of command is determined: a special built-in command,
a function, a normal builtin, or the name of a file to execute found using the
PATH
parameter.
The checks are made in the above order.
Special built-in commands differ from other commands in that the
PATH
parameter is not used to find them, an error during their execution can
cause a non-interactive shell to exit, and parameter assignments that are
specified before the command are kept after the command completes.
Regular built-in commands are different only in that the
PATH
parameter is not used to find them.
The original
ksh
and POSIX differ somewhat in which commands are considered
special or regular.
POSIX special built-in utilities:
. , : , break , continue
eval , exec , exit , export
readonly , return , set , shift
times , trap , unset
Additional
commands keeping assignments:
builtin , global , typeset , wait
Builtins that are not special:
[ , alias , bg , bind
cat , cd , command , echo
false , fc , fg , getopts
jobs , kill , let , mknod
print , pwd , read , realpath
rename , sleep , suspend , test
true , ulimit , umask , unalias
whence
Once the type of command has been determined, any command-line parameter
assignments are performed and exported for the duration of the command.
The following describes the special and regular built-in commands:
- . file [arg ...
]
-
This is called the
``dot''
command.
Execute the commands in
file
in the current environment.
The file is searched for in the directories of
PATH
If arguments are given, the positional parameters may be used to access them
while
file
is being executed.
If no arguments are given, the positional parameters are
those of the environment the command is used in.
- : [...
]
-
The null command.
Exit status is set to zero.
- [ expression ]
-
See
test
-
alias
[-d | t [-r |]
+-x ]
[-p
]
[+
]
[name
[= value
]
... ]
-
- Without arguments,
alias
lists all aliases.
For any name without a value, the existing alias is listed.
Any name with a value defines an alias (see
Sx Aliases
above).
When listing aliases, one of two formats is used.
Normally, aliases are listed as
name = value
where
value
is quoted.
If options were preceded with
`+'
,
or a lone
`+'
is given on the command line, only
name
is printed.
The
-d
option causes directory aliases which are used in tilde expansion to be
listed or set (see
Sx Tilde expansion
above).
If the
-p
option is used, each alias is prefixed with the string
``alias ''
The
-t
option indicates that tracked aliases are to be listed/set (values specified on
the command line are ignored for tracked aliases).
The
-r
option indicates that all tracked aliases are to be reset.
The
-x
option sets
(+x clears
)
the export attribute of an alias, or, if no names are given, lists the aliases
with the export attribute (exporting an alias has no effect).
- bg [job ...
]
-
Resume the specified stopped job(s) in the background.
If no jobs are specified,
%+
is assumed.
See
Sx Job control
below for more information.
- bind [-l
]
-
The current bindings are listed.
If the
-l
flag is given,
bind
instead lists the names of the functions to which keys may be bound.
See
Sx Emacs editing mode
for more information.
-
bind [-m
]
string = [substitute
]
...
-
-
bind
string = [editing-command
]
...
-
- The specified editing command is bound to the given
string
which should consist of a control character
optionally preceded by one of the two prefix characters
and optionally succeded by a tilde character.
Future input of the
string
will cause the editing command to be immediately invoked.
If the
-m
flag is given, the specified input
string
will afterwards be immediately replaced by the given
substitute
string which may contain editing commands but not other macros.
If a tilde postfix is given, a tilde trailing the one or
two prefices and the control character is ignored, any
other trailing character will be processed afterwards.
Control characters may be written using caret notation
i.e. ^X represents Ctrl-X.
Note that although only two prefix characters (usually ESC and ^X)
are supported, some multi-character sequences can be supported.
The following default bindings show how the arrow keys, the home, end and
delete key on a BSD wsvt25, xterm-xfree86 or GNU screen terminal are bound
(of course some escape sequences won't work out quite this nicely):
bind '^X'=prefix-2
bind '^[['=prefix-2
bind '^XA'=up-history
bind '^XB'=down-history
bind '^XC'=forward-char
bind '^XD'=backward-char
bind '^X1~'=beginning-of-line
bind '^X7~'=beginning-of-line
bind '^XH'=beginning-of-line
bind '^X4~'=end-of-line
bind '^X8~'=end-of-line
bind '^XF'=end-of-line
bind '^X3~'=delete-char-forward
- break [level
]
-
Exit the
level th
inner-most
for
select
until
or
while
loop.
level
defaults to 1.
-
builtin
[--
]
command [arg ...
]
-
- Execute the built-in command
command
-
cat
[-u
]
[file ...
]
-
- Read files sequentially, in command line order, and write them to
standard output.
If a
file
is a single dash
(`-'
)
or absent, read from standard input.
Unless compiled with
MKSH_NO_EXTERNAL_CAT
if any options are given, an external
cat(1)
utility is invoked instead if called from the shell.
For direct builtin calls, the
POSIX
-u
option is supported as a no-op.
-
cd
[-L
]
[dir
]
-
-
cd
-P [-e
]
[dir
]
-
-
chdir
[-eLP
]
[dir
]
-
- Set the working directory to
dir
If the parameter
CDPATH
is set, it lists the search path for the directory containing
dir
A
NULL
path means the current directory.
If
dir
is found in any component of the
CDPATH
search path other than the
NULL
path, the name of the new working directory will be written to standard output.
If
dir
is missing, the home directory
HOME
is used.
If
dir
is
`-'
,
the previous working directory is used (see the
OLDPWD
parameter).
If the
-L
option (logical path) is used or if the
physical
option isn't set (see the
set
command below), references to
`..'
in
dir
are relative to the path used to get to the directory.
If the
-P
option (physical path) is used or if the
physical
option is set,
`..'
is relative to the filesystem directory tree.
The
PWD
and
OLDPWD
parameters are updated to reflect the current and old working directory,
respectively.
If the
-e
option is set for physical filesystem traversal, and
PWD
could not be set, the exit code is 1; greater than 1 if an
error occurred, 0 otherwise.
-
cd
[-eLP
]
old new
-
-
chdir
[-eLP
]
old new
-
- The string
new
is substituted for
old
in the current directory, and the shell attempts to change to the new
directory.
-
command
[-pVv cmd
]
[arg ...
]
-
- If neither the
-v
nor
-V
option is given,
cmd
is executed exactly as if
command
had not been specified, with two exceptions:
firstly,
cmd
cannot be a shell function;
and secondly, special built-in commands lose their specialness
(i.e. redirection and utility errors do not cause the shell to
exit, and command assignments are not permanent).
If the
-p
option is given, a default search path is used instead of the current value of
PATH
the actual value of which is system dependent.
If the
-v
option is given, instead of executing
cmd
information about what would be executed is given (and the same is done for
arg ... )
For special and regular built-in commands and functions, their names are simply
printed; for aliases, a command that defines them is printed; and for commands
found by searching the
PATH
parameter, the full path of the command is printed.
If no command is found
(i.e. the path search fails), nothing is printed and
command
exits with a non-zero status.
The
-V
option is like the
-v
option, except it is more verbose.
- continue [level
]
-
Jumps to the beginning of the
level th
inner-most
for
select
until
or
while
loop.
level
defaults to 1.
-
echo
[-Een
]
[arg ...
]
-
Warning:
- this utility is not portable; use the Korn shell builtin
print
instead.
Prints its arguments (separated by spaces) followed by a newline, to the
standard output.
The newline is suppressed if any of the arguments contain the
backslash sequence
`\c'
See the
print
command below for a list of other backslash sequences that are recognised.
The options are provided for compatibility with
BSD shell scripts.
The
-n
option suppresses the trailing newline,
-e
enables backslash interpretation (a no-op, since this is normally done), and
-E
suppresses backslash interpretation.
If the
posix
or
sh
option is set or this is a direct builtin call, only the first argument
is treated as an option, and only if it is exactly
``-n
''
Backslash interpretation is disabled.
- eval command ...
-
The arguments are concatenated (with spaces between them) to form a single
string which the shell then parses and executes in the current environment.
-
exec
[command [arg ...
]
]
-
- The command is executed without forking, replacing the shell process.
If no command is given except for I/O redirection, the I/O redirection is
permanent and the shell is
not replaced.
Any file descriptors greater than 2 which are opened or
dup(2)Ns'd
in this way are not made available to other executed commands (i.e. commands
that are not built-in to the shell).
Note that the Bourne shell differs here;
it does pass these file descriptors on.
- exit [status
]
-
The shell exits with the specified exit status.
If
status
is not specified, the exit status is the current value of the
$?
parameter.
-
export
[-p
]
[parameter [= value
]
]
-
- Sets the export attribute of the named parameters.
Exported parameters are passed in the environment to executed commands.
If values are specified, the named parameters are also assigned.
If no parameters are specified, all parameters with the export attribute
set are printed one per line; either their names, or, if a
`-'
with no option letter is specified, name=value pairs, or, with
-p
export
commands suitable for re-entry.
- false
-
A command that exits with a non-zero status.
-
fc
[-e editor |
-l [-n ]
]
[-r
]
[first [last
]
]
-
first
- and
last
select commands from the history.
Commands can be selected by history number
(negative numbers go backwards from the current, most recent, line)
or a string specifying the most recent command starting with that string.
The
-l
option lists the command on standard output, and
-n
inhibits the default command numbers.
The
-r
option reverses the order of the list.
Without
-l
the selected commands are edited by the editor specified with the
-e
option, or if no
-e
is specified, the editor specified by the
FCEDIT
parameter (if this parameter is not set,
/bin/ed
is used), and then executed by the shell.
-
fc
-e - | -s
[-g
]
[old = new
]
[prefix
]
-
- Re-execute the selected command (the previous command by default) after
performing the optional substitution of
old
with
new
If
-g
is specified, all occurrences of
old
are replaced with
new
The meaning of
-e -
and
-s
is identical: re-execute the selected command without invoking an editor.
This command is usually accessed with the predefined:
alias r='fc -e -'
- fg [job ...
]
-
Resume the specified job(s) in the foreground.
If no jobs are specified,
%+
is assumed.
See
Sx Job control
below for more information.
-
getopts
optstring name
[arg ...
]
-
- Used by shell procedures to parse the specified arguments (or positional
parameters, if no arguments are given) and to check for legal options.
optstring
contains the option letters that
getopts
is to recognise.
If a letter is followed by a colon, the option is expected to
have an argument.
Options that do not take arguments may be grouped in a single argument.
If an option takes an argument and the option character is not the
last character of the argument it is found in, the remainder of the argument is
taken to be the option's argument; otherwise, the next argument is the option's
argument.
Each time
getopts
is invoked, it places the next option in the shell parameter
name
and the index of the argument to be processed by the next call to
getopts
in the shell parameter
OPTIND
If the option was introduced with a
`+'
,
the option placed in
name
is prefixed with a
`+'
When an option requires an argument,
getopts
places it in the shell parameter
OPTARG
When an illegal option or a missing option argument is encountered, a question
mark or a colon is placed in
name
(indicating an illegal option or missing argument, respectively) and
OPTARG
is set to the option character that caused the problem.
Furthermore, if
optstring
does not begin with a colon, a question mark is placed in
name
OPTARG
is unset, and an error message is printed to standard error.
When the end of the options is encountered,
getopts
exits with a non-zero exit status.
Options end at the first (non-option
argument) argument that does not start with a
`-'
,
or when a
`--'
argument is encountered.
Option parsing can be reset by setting
OPTIND
to 1 (this is done automatically whenever the shell or a shell procedure is
invoked).
Warning: Changing the value of the shell parameter
OPTIND
to a value other than 1, or parsing different sets of arguments without
resetting
OPTIND
may lead to unexpected results.
- global ...
-
See
typeset
-
hash
[-r
]
[name ...
]
-
- Without arguments, any hashed executable command pathnames are listed.
The
-r
option causes all hashed commands to be removed from the hash table.
Each
name
is searched as if it were a command name and added to the hash table if it is
an executable command.
-
jobs
[-lnp
]
[job ...
]
-
- Display information about the specified job(s); if no jobs are specified, all
jobs are displayed.
The
-n
option causes information to be displayed only for jobs that have changed
state since the last notification.
If the
-l
option is used, the process ID of each process in a job is also listed.
The
-p
option causes only the process group of each job to be printed.
See
Sx Job control
below for the format of
job
and the displayed job.
-
kill
[-s signame |
- signum |
- signame ]
{ job | pid | pgrp }
...
-
- Send the specified signal to the specified jobs, process IDs, or process
groups.
If no signal is specified, the
TERM
signal is sent.
If a job is specified, the signal is sent to the job's process group.
See
Sx Job control
below for the format of
job
-
kill
-l
[exit-status ...
]
-
- Print the signal name corresponding to
exit-status
If no arguments are specified, a list of all the signals, their numbers, and
a short description of them are printed.
- let [expression ...
]
-
Each expression is evaluated (see
Sx Arithmetic expressions
above).
If all expressions are successfully evaluated, the exit status is 0 (1)
if the last expression evaluated to non-zero (zero).
If an error occurs during
the parsing or evaluation of an expression, the exit status is greater than 1.
Since expressions may need to be quoted,
(( expr ))
is syntactic sugar for
let expr
- let]
-
Internally used alias for
let
-
mknod
[-m mode
]
name
b|c
major minor
-
-
mknod
[-m mode
]
name
p
-
- Create a device special file.
The file type may be
b
(block type device),
c
(character type device),
or
p
(named pipe , FIFO
)
The file created may be modified according to its
mode
(via the
-m
option),
major
(major device number),
and
minor
(minor device number).
See
mknod(8)
for further information.
-
print
[-nprsu [n |]
-R [-en ]
]
[argument ...
]
-
print
- prints its arguments on the standard output, separated by spaces and
terminated with a newline.
The
-n
option suppresses the newline.
By default, certain C escapes are translated.
These include these mentioned in
Sx Backslash expansion
above, as well as
`\c'
,
which is equivalent to using the
-n
option.
Backslash expansion may be inhibited with the
-r
option.
The
-s
option prints to the history file instead of standard output; the
-u
option prints to file descriptor
n
Po n
defaults to 1 if omitted
Pc ;
and the
-p
option prints to the co-process (see
Sx Co-processes
above).
The
-R
option is used to emulate, to some degree, the
BSD echo(1)
command which does not process
`\'
sequences unless the
-e
option is given.
As above, the
-n
option suppresses the trailing newline.
- printf format [arguments ...
]
-
Formatted output.
Approximately the same as the
printf(1),
utility, except it uses the same
Sx Backslash expansion
and I/O code and does hot handle floating point as the rest of
mksh
This is not normally part of
mksh
however, distributors may have added this as builtin as a speed hack.
Do not use in new code.
- pwd [-LP
]
-
Print the present working directory.
If the
-L
option is used or if the
physical
option isn't set (see the
set
command below), the logical path is printed (i.e. the path used to
cd
to the current directory).
If the
-P
option (physical path) is used or if the
physical
option is set, the path determined from the filesystem (by following
`..'
directories to the root directory) is printed.
-
read
[-A | -a
]
[-d x
]
[-N z |
-n z ]
[-p |
-u [n
]
[-t n
]
]
[-rs
]
[p ...
]
-
- Reads a line of input, separates the input into fields using the
IFS
parameter (see
Sx Substitution
above), and assigns each field to the specified parameters
p
If no parameters are specified, the
REPLY
parameter is used to store the result.
With the
-A
and
-a
options, only no or one parameter is accepted.
If there are more parameters than fields, the extra parameters are set to
the empty string or 0; if there are more fields than parameters, the last
parameter is assigned the remaining fields (including the word separators).
The options are as follows:
- -A
-
Store the result into the parameter
p
(or
REPLY
as array of words.
- -a
-
Store the result without word splitting into the parameter
p
(or
REPLY
as array of characters (wide characters if the
utf8-mode
option is enacted, octets otherwise).
- -d x
-
Use the first byte of
x
NUL
if empty, instead of the ASCII newline character as input line delimiter.
- -N z
-
Instead of reading till end-of-line, read exactly
z
bytes; less if EOF or a timeout occurs.
- -n z
-
Instead of reading till end-of-line, read up to
z
bytes but return as soon as any bytes are read, e.g. from a
slow terminal device, or if EOF or a timeout occurs.
- -p
-
Read from the currently active co-process, see
Sx Co-processes
above for details on this.
- -u [n
]
-
Read from the file descriptor
n
(defaults to 0, i.e. standard input).
The argument must immediately follow the option character.
- -t n
-
Interrupt reading after
n
seconds (specified as positive decimal value with an optional fractional part).
- -r
-
Normally, the ASCII backslash character escapes the special
meaning of the following character and is stripped from the input;
read
does not stop when encountering a backslash-newline sequence and
does not store that newline in the result.
This option enables raw mode, in which backslashes are not processed.
- -s
-
The input line is saved to the history.
If the input is a terminal, both the
-N
and
-n
options set it into raw mode;
they read an entire file if -1 is passed as
z
argument.
The first parameter may have a question mark and a string appended to it, in
which case the string is used as a prompt (printed to standard error before
any input is read) if the input is a
tty(4)
(e.g.
read nfoo?'number of foos: ' )
If no input is read or a timeout occurred,
read
exits with a non-zero status.
Another handy set of tricks:
If
read
is run in a loop such as
while read foo; do ...; done
then leading whitespace will be removed (IFS) and backslashes processed.
You might want to use
while IFS= read -r foo; do ...; done
for pristine I/O.
Similarily, when using the
-a
option, use of the
-r
option might be prudent; the same applies for:
find . -type f -print0 | \
while IFS= read -d '' -r filename; do
print -r -- "found <${filename#./}>"
done
The inner loop will be executed in a subshell and variable changes
cannot be propagated if executed in a pipeline:
bar | baz | while read foo; do ...; done
Use co-processes instead:
bar | baz |&
while read -p foo; do ...; done
exec 3>&p; exec 3>&-
-
readonly
[-p
]
[parameter
[= value
]
... ]
-
- Sets the read-only attribute of the named parameters.
If values are given,
parameters are set to them before setting the attribute.
Once a parameter is
made read-only, it cannot be unset and its value cannot be changed.
If no parameters are specified, the names of all parameters with the read-only
attribute are printed one per line, unless the
-p
option is used, in which case
readonly
commands defining all read-only parameters, including their values, are
printed.
-
realpath
[--
]
name
-
- Prints the resolved absolute pathname corresponding to
name
If
name
ends with a slash
(`/'
)
it's also checked for existence and whether it is a directory; otherwise,
realpath
returns 0 if the pathname either exists or can be created immediately,
i.e. all but the last component exist and are directories.
-
rename
[--
]
from to
-
- Renames the file
from
to
to
Both must be complete pathnames and on the same device.
This builtin is intended for emergency situations where
/bin/mv
becomes unusable, and directly calls
rename(2).
- return [status
]
-
Returns from a function or
.
script, with exit status
status
If no
status
is given, the exit status of the last executed command is used.
If used outside of a function or
.
script, it has the same effect as
exit
Note that
treats both profile and
ENV
files as
.
scripts, while the original Korn shell only treats profiles as
.
scripts.
-
set [+-abCefhiklmnprsUuvXx [+-o option
]
]
[+-A name
]
[--
]
[arg ...
]
-
- The
set
command can be used to set
(-
)
or clear
(+
)
shell options, set the positional parameters, or set an array parameter.
Options can be changed using the
+-o option
syntax, where
option
is the long name of an option, or using the
+- letter
syntax, where
letter
is the option's single letter name (not all options have a single letter name).
The following table lists both option letters (if they exist) and long names
along with a description of what the option does:
- -A name
-
Sets the elements of the array parameter
name
to
arg ...
If
-A
is used, the array is reset (i.e. emptied) first; if
+A
is used, the first N elements are set (where N is the number of arguments);
the rest are left untouched.
An alternative syntax for the command
set -A foo -- a b c
which is compatible to
GNU
bash
and also supported by
AT&T System
ksh93
is:
foo=(a b c); foo+=(d e)
Another
AT&T System
ksh93
and
GNU
bash
extension allows specifying the indices used for
arg ...
(from the above example, a b c
)
like this:
set -A foo -- [0]=a [1]=b [2]=c
or
foo=([0]=a [1]=b [2]=c)
which can also be written
foo=([0]=a b c)
because indices are incremented automatically.
- -a | -o allexport
-
All new parameters are created with the export attribute.
- -b | -o notify
-
Print job notification messages asynchronously, instead of just before the
prompt.
Only used if job control is enabled
(-m
)
- -C | -o noclobber
-
Prevent > redirection from overwriting existing files.
Instead, >| must be used to force an overwrite.
Note that this is not safe to use for creation of temporary files or
lockfiles due to a TOCTOU in a check allowing one to redirect output to
/dev/null
or other device files even in
noclobber
mode.
- -e | -o errexit
-
Exit (after executing the
ERR
trap) as soon as an error occurs or a command fails (i.e. exits with a
non-zero status).
This does not apply to commands whose exit status is
explicitly tested by a shell construct such as
if
until
while
or
!
statements.
For
&&
or
||
only the status of the last command is tested.
- -f | -o noglob
-
Do not expand file name patterns.
- -h | -o trackall
-
Create tracked aliases for all executed commands (see
Sx Aliases
above).
Enabled by default for non-interactive shells.
- -i | -o interactive
-
The shell is an interactive shell.
This option can only be used when the shell is invoked.
See above for a description of what this means.
- -k | -o keyword
-
Parameter assignments are recognised anywhere in a command.
- -l | -o login
-
The shell is a login shell.
This option can only be used when the shell is invoked.
See above for a description of what this means.
- -m | -o monitor
-
Enable job control (default for interactive shells).
- -n | -o noexec
-
Do not execute any commands.
Useful for checking the syntax of scripts
(ignored if interactive).
- -p | -o privileged
-
The shell is a privileged shell.
It is set automatically if, when the shell starts,
the real UID or GID does not match
the effective UID (EUID) or GID (EGID), respectively.
See above for a description of what this means.
- -r | -o restricted
-
The shell is a restricted shell.
This option can only be used when the shell is invoked.
See above for a description of what this means.
- -s | -o stdin
-
If used when the shell is invoked, commands are read from standard input.
Set automatically if the shell is invoked with no arguments.
When
-s
is used with the
set
command it causes the specified arguments to be sorted before assigning them to
the positional parameters (or to array
name
if
-A
is used).
- -U | -o utf8-mode
-
Enable UTF-8 support in the
Sx Emacs editing mode
and internal string handling functions.
This flag is disabled by default, but can be enabled by setting it on the
shell command line; is enabled automatically for interactive shells if
requested at compile time, your system supports
Fn setlocale LC_CTYPE
and optionally
Fn nl_langinfo CODESET ,
or the
LC_ALL
LC_CTYPE
or
LANG
environment variables,
and at least one of these returns something that matches
``UTF-8''
or
``utf8''
case-insensitively; for direct builtin calls depending on the
aforementioned environment variables; or for stdin or scripts,
if the input begins with a UTF-8 Byte Order Mark.
- -u | -o nounset
-
Referencing of an unset parameter, other than
``$@''
or
``$*''
is treated as an error, unless one of the
`-'
,
`+'
,
or
`='
modifiers is used.
- -v | -o verbose
-
Write shell input to standard error as it is read.
- -X | -o markdirs
-
Mark directories with a trailing
`/'
during file name generation.
- -x | -o xtrace
-
Print command trees when they are executed, preceded by
the value of
PS4
- -o bgnice
-
Background jobs are run with lower priority.
- -o braceexpand
-
Enable brace expansion (a.k.a. alternation).
This is enabled by default.
If disabled, tilde expansion after an equals sign is disabled as a side effect.
- -o emacs
-
Enable BRL emacs-like command-line editing (interactive shells only); see
Sx Emacs editing mode .
- -o gmacs
-
Enable gmacs-like command-line editing (interactive shells only).
Currently identical to emacs editing except that transpose-chars (^T) acts
slightly differently.
- -o ignoreeof
-
The shell will not (easily) exit when end-of-file is read;
exit
must be used.
To avoid infinite loops, the shell will exit if
EOF
is read 13 times in a row.
- -o inherit-xtrace
-
Do not reset
-o xtrace
upon entering functions.
This is enabled by default.
- -o nohup
-
Do not kill running jobs with a
SIGHUP
signal when a login shell exits.
Currently set by default, but this may
change in the future to be compatible with
AT&T System
ksh
which
doesn't have this option, but does send the
SIGHUP
signal.
- -o nolog
-
No effect.
In the original Korn shell, this prevents function definitions from
being stored in the history file.
- -o physical
-
Causes the
cd
and
pwd
commands to use
``physical''
(i.e. the filesystem's)
`..'
directories instead of
``logical''
directories (i.e. the shell handles
`..'
which allows the user to be oblivious of symbolic links to directories).
Clear by default.
Note that setting this option does not affect the current value of the
PWD
parameter; only the
cd
command changes
PWD
See the
cd
and
pwd
commands above for more details.
- -o pipefail
-
Make the exit status of a pipeline (before logically complementing) the
rightmost non-zero errorlevel, or zero if all commands exited with zero.
- -o posix
-
Enable a somewhat more
Px ish mode.
As a side effect, setting this flag turns off
braceexpand
mode, which can be turned back on manually, and
sh
mode.
- -o sh
-
Enable
/bin/sh
(kludge)
mode.
Automatically enabled if the basename of the shell invocation begins with
``sh''
and this autodetection feature is compiled in
(not in MirBSD)
As a side effect, setting this flag turns off
braceexpand
mode, which can be turned back on manually, and
posix
mode.
- -o vi
-
Enable
vi(1)Ns-like
command-line editing (interactive shells only).
See
Sx Vi editing mode
for documentation and limitations.
- -o vi-esccomplete
-
In vi command-line editing, do command and file name completion when escape
(^[) is entered in command mode.
- -o vi-tabcomplete
-
In vi command-line editing, do command and file name completion when tab (^I)
is entered in insert mode.
This is the default.
- -o viraw
-
No effect.
In the original Korn shell, unless
viraw
was set, the vi command-line mode would let the
tty(4)
driver do the work until ESC (^[) was entered.
is always in viraw mode.
These options can also be used upon invocation of the shell.
The current set of
options (with single letter names) can be found in the parameter
`$-'
set -o
with no option name will list all the options and whether each is on or off;
set +o
will print the long names of all options that are currently on.
Remaining arguments, if any, are positional parameters and are assigned, in
order, to the positional parameters (i.e. $1, $2, etc.).
If options end with
`--'
and there are no remaining arguments, all positional parameters are cleared.
If no options or arguments are given, the values of all names are printed.
For unknown historical reasons, a lone
`-'
option is treated specially --- it clears both the
-v
and
-x
options.
- shift [number
]
-
The positional parameters
number +1
number +2
etc. are renamed to
`1'
`2'
etc.
number
defaults to 1.
- sleep seconds
-
Suspends execution for a minimum of the
seconds
specified as positive decimal value with an optional fractional part.
Signal delivery may continue execution earlier.
- source file [arg ...
]
-
Like
. Po Do dot Dc Pc ,
except that the current working directory is appended to the
PATH
in GNU
bash
and
mksh
In
ksh93
and
mksh
this is implemented as a shell alias instead of a builtin.
- suspend
-
Stops the shell as if it had received the suspend character from
the terminal.
It is not possible to suspend a login shell unless the parent process
is a member of the same terminal session but is a member of a different
process group.
As a general rule, if the shell was started by another shell or via
su(1),
it can be suspended.
- test expression
-
- [ expression ]
-
test
evaluates the
expression
and returns zero status if true, 1 if false, or greater than 1 if there
was an error.
It is normally used as the condition command of
if
and
while
statements.
Symbolic links are followed for all
file
expressions except
-h
and
-L
The following basic expressions are available:
- -a file
-
file
exists.
- -b file
-
file
is a block special device.
- -c file
-
file
is a character special device.
- -d file
-
file
is a directory.
- -e file
-
file
exists.
- -f file
-
file
is a regular file.
- -G file
-
file 's
group is the shell's effective group ID.
- -g file
-
file 's
mode has the setgid bit set.
- -H file
-
file
is a context dependent directory (only useful on HP-UX).
- -h file
-
file
is a symbolic link.
- -k file
-
file 's
mode has the
sticky(8)
bit set.
- -L file
-
file
is a symbolic link.
- -O file
-
file 's
owner is the shell's effective user ID.
- -o option
-
Shell
option
is set (see the
set
command above for a list of options).
As a non-standard extension, if the option starts with a
`!'
,
the test is negated; the test always fails if
option
doesn't exist (so [ -o foo -o -o !foo ] returns true if and only if option
foo
exists).
The same can be achieved with [ -o ?foo ] like in
AT&T System
ksh93
option
can also be the short flag led by either
`-'
or
`+'
(no logical negation)
for example
`-x'
or
`+x'
instead of
`xtrace'
- -p file
-
file
is a named pipe
(FIFO
)
- -r file
-
file
exists and is readable.
- -S file
-
file
is a
unix(4)Ns-domain
socket.
- -s file
-
file
is not empty.
- -t fd
-
File descriptor
fd
is a
tty(4)
device.
- -u file
-
file 's
mode has the setuid bit set.
- -w file
-
file
exists and is writable.
- -x file
-
file
exists and is executable.
- file1 -nt file2
-
file1
is newer than
file2
or
file1
exists and
file2
does not.
- file1 -ot file2
-
file1
is older than
file2
or
file2
exists and
file1
does not.
- file1 -ef file2
-
file1
is the same file as
file2
- string
-
string
has non-zero length.
- -n string
-
string
is not empty.
- -z string
-
string
is empty.
- string = string
-
Strings are equal.
- string == string
-
Strings are equal.
- string > string
-
First string operand is greater than second string operand.
- string < string
-
First string operand is less than second string operand.
- string != string
-
Strings are not equal.
- number -eq number
-
Numbers compare equal.
- number -ne number
-
Numbers compare not equal.
- number -ge number
-
Numbers compare greater than or equal.
- number -gt number
-
Numbers compare greater than.
- number -le number
-
Numbers compare less than or equal.
- number -lt number
-
Numbers compare less than.
The above basic expressions, in which unary operators have precedence over
binary operators, may be combined with the following operators (listed in
increasing order of precedence):
expr -o expr Logical OR.
expr -a expr Logical AND.
! expr Logical NOT.
( expr ) Grouping.
Note that a number actually may be an arithmetic expression, such as
a mathematical term or the name of an integer variable:
x=1; [ "x" -eq 1 ] evaluates to true
Note that some special rules are applied (courtesy of
Px ) if the number of arguments to
test
or inside the brackets
[ ... ]
is less than five: if leading
`!'
arguments can be stripped such that only one to three arguments remain,
then the lowered comparison is executed; (thanks to XSI) parentheses
\( ... \)
lower four- and three-argument forms to two- and one-argument forms,
respectively; three-argument forms ultimately prefer binary operations,
followed by negation and parenthesis lowering; two- and four-argument forms
prefer negation followed by parenthesis; the one-argument form always implies
-n
Note
A common mistake is to use
``if [ $foo = bar ]''
which fails if parameter
``foo''
is
NULL
or unset, if it has embedded spaces (i.e.
IFS
octets), or if it is a unary operator like
`!'
or
`-n
'
Use tests like
``if [ x$foo = xbar ]''
instead, or the double-bracket operator
``if [[ $foo = bar ]]''
or, to avoid pattern matching (see
[[
above):
``if [[ $foo = $bar ]]''
The
[[ ... ]]
construct is not only more secure to use but also often faster.
-
time
[-p
]
[pipeline
]
-
- If a
pipeline
is given, the times used to execute the pipeline are reported.
If no pipeline
is given, then the user and system time used by the shell itself, and all the
commands it has run since it was started, are reported.
The times reported are the real time (elapsed time from start to finish),
the user CPU time (time spent running in user mode), and the system CPU time
(time spent running in kernel mode).
Times are reported to standard error; the format of the output is:
"0m0.00s real 0m0.00s user 0m0.00s system"
If the
-p
option is given the output is slightly longer:
real 0.00
user 0.00
sys 0.00
It is an error to specify the
-p
option unless
pipeline
is a simple command.
Simple redirections of standard error do not affect the output of the
time
command:
$ time sleep 1 2>afile
$ { time sleep 1; } 2>afile
Times for the first command do not go to
``afile''
but those of the second command do.
- times
-
Print the accumulated user and system times used both by the shell
and by processes that the shell started which have exited.
The format of the output is:
0m0.00s 0m0.00s
0m0.00s 0m0.00s
- trap [handler signal ...
]
-
Sets a trap handler that is to be executed when any of the specified signals are
received.
handler
is either a
NULL
string, indicating the signals are to be ignored, a minus sign
(`-'
)
indicating that the default action is to be taken for the signals (see
signal(3)),
or a string containing shell commands to be evaluated and executed at the first
opportunity (i.e. when the current command completes, or before printing the
next
PS1
prompt) after receipt of one of the signals.
signal
is the name of a signal (e.g.
PIPE
or
ALRM
or the number of the signal (see the
kill -l
command above).
There are two special signals:
EXIT
(also known as 0) which is executed when the shell is about to exit, and
ERR
which is executed after an error occurs (an error is something that would cause
the shell to exit if the
-e
or
errexit
option were set --- see the
set
command above).
EXIT
handlers are executed in the environment of the last executed command.
Note
that for non-interactive shells, the trap handler cannot be changed for signals
that were ignored when the shell started.
With no arguments,
trap
lists, as a series of
trap
commands, the current state of the traps that have been set since the shell
started.
Note that the output of
trap
cannot be usefully piped to another process (an artifact of the fact that
traps are cleared when subprocesses are created).
The original Korn shell's
DEBUG
trap and the handling of
ERR
and
EXIT
traps in functions are not yet implemented.
- true
-
A command that exits with a zero value.
-
global
[[+-alpnrtUux
]
[-L [n
]
]
[-R [n
]
]
[-Z [n
]
]
[-i [n
]
]
| -f [-tux ]
]
[name
[= value
]
... ]
-
-
typeset
[[+-alpnrtUux
]
[-LRZ [n
]
]
[-i [n
]
]
| -f [-tux ]
]
[name
[= value
]
... ]
-
- Display or set parameter attributes.
With no
name
arguments, parameter attributes are displayed; if no options are used, the
current attributes of all parameters are printed as
typeset
commands; if an option is given (or
`-'
with no option letter), all parameters and their values with the specified
attributes are printed; if options are introduced with
`+'
,
parameter values are not printed.
If
name
arguments are given, the attributes of the named parameters are set
(-
)
or cleared
(+
)
Values for parameters may optionally be specified.
For
name [*]
the change affects the entire array, and no value may be specified.
If
typeset
is used inside a function, any parameters specified are localised.
This is not done by the otherwise identical
global
Note
This means that
's global
command is
not
equivalent to other programming languages' as it does not allow a
function called from another function to access a parameter at truly
global scope, but only prevents putting an accessed one into local scope.
When
-f
is used,
typeset
operates on the attributes of functions.
As with parameters, if no
name
arguments are given,
functions are listed with their values (i.e. definitions) unless
options are introduced with
`+'
,
in which case only the function names are reported.
- -a
-
Indexed array attribute.
- -f
-
Function mode.
Display or set functions and their attributes, instead of parameters.
- -i [n
]
-
Integer attribute.
n
specifies the base to use when displaying the integer (if not specified, the
base given in the first assignment is used).
Parameters with this attribute may
be assigned values containing arithmetic expressions.
- -L [n
]
-
Left justify attribute.
n
specifies the field width.
If
n
is not specified, the current width of a parameter (or the width of its first
assigned value) is used.
Leading whitespace (and zeros, if used with the
-Z
option) is stripped.
If necessary, values are either truncated or space padded
to fit the field width.
- -l
-
Lower case attribute.
All upper case characters in values are converted to lower case.
(In the original Korn shell, this parameter meant
``long integer''
when used with the
-i
option.)
- -n
-
Create a bound variable (name reference): any access to the variable
name
will access the variable
value
in the current scope (this is different from
AT&T System
ksh93 !
instead.
Also different from
AT&T System
ksh93
is that
value
is lazily evaluated at the time
name
is accessed.
This can be used by functions to access variables whose names are
passed as parametres, instead of using
eval
- -p
-
Print complete
typeset
commands that can be used to re-create the attributes and values of
parameters.
- -R [n
]
-
Right justify attribute.
n
specifies the field width.
If
n
is not specified, the current width of a parameter (or the width of its first
assigned value) is used.
Trailing whitespace is stripped.
If necessary, values are either stripped of leading characters or space
padded to make them fit the field width.
- -r
-
Read-only attribute.
Parameters with this attribute may not be assigned to or unset.
Once this attribute is set, it cannot be turned off.
- -t
-
Tag attribute.
Has no meaning to the shell; provided for application use.
For functions,
-t
is the trace attribute.
When functions with the trace attribute are executed, the
xtrace
(-x
)
shell option is temporarily turned on.
- -U
-
Unsigned integer attribute.
Integers are printed as unsigned values (combine with the
-i
option).
This option is not in the original Korn shell.
- -u
-
Upper case attribute.
All lower case characters in values are converted to upper case.
(In the original Korn shell, this parameter meant
``unsigned integer''
when used with the
-i
option which meant upper case letters would never be used for bases greater
than 10.
See the
-U
option.)
For functions,
-u
is the undefined attribute.
See
Sx Functions
above for the implications of this.
- -x
-
Export attribute.
Parameters (or functions) are placed in the environment of
any executed commands.
Exported functions are not yet implemented.
- -Z [n
]
-
Zero fill attribute.
If not combined with
-L
this is the same as
-R
except zero padding is used instead of space padding.
For integers, the number instead of the base is padded.
If any of the
-i
-L
-l
-R
-U
-u
or
-Z
options are changed, all others from this set are cleared,
unless they are also given on the same command line.
-
ulimit
[-aBCcdefHilMmnOPpqrSsTtVvw
]
[value
]
-
- Display or set process limits.
If no options are used, the file size limit
(-f
)
is assumed.
value
if specified, may be either an arithmetic expression or the word
``unlimited''
The limits affect the shell and any processes created by the shell after a
limit is imposed.
Note that some systems may not allow limits to be increased
once they are set.
Also note that the types of limits available are system
dependent --- some systems have only the
-f
limit.
- -a
-
Display all limits; unless
-H
is used, soft limits are displayed.
- -B n
-
Set the socket buffer size to
n
kibibytes.
- -C n
-
Set the number of cached threads to
n
- -c n
-
Impose a size limit of
n
blocks on the size of core dumps.
- -d n
-
Impose a size limit of
n
kibibytes on the size of the data area.
- -e n
-
Set the maximum niceness to
n
- -f n
-
Impose a size limit of
n
blocks on files written by the shell and its child processes (files of any
size may be read).
- -H
-
Set the hard limit only (the default is to set both hard and soft limits).
- -i n
-
Set the number of pending signals to
n
- -l n
-
Impose a limit of
n
kibibytes on the amount of locked (wired) physical memory.
- -M n
-
Set the AIO locked memory to
n
kibibytes.
- -m n
-
Impose a limit of
n
kibibytes on the amount of physical memory used.
- -n n
-
Impose a limit of
n
file descriptors that can be open at once.
- -O n
-
Set the number of AIO operations to
n
- -P n
-
Limit the number of threads per process to
n
- -p n
-
Impose a limit of
n
processes that can be run by the user at any one time.
- -q n
-
Limit the size of
POSIX
message queues to
n
bytes.
- -r n
-
Set the maximum real-time priority to
n
- -S
-
Set the soft limit only (the default is to set both hard and soft limits).
- -s n
-
Impose a size limit of
n
kibibytes on the size of the stack area.
- -T n
-
Impose a time limit of
n
real seconds to be used by each process.
- -t n
-
Impose a time limit of
n
CPU seconds spent in user mode to be used by each process.
- -V n
-
Set the number of vnode monitors on Haiku to
n
- -v n
-
Impose a limit of
n
kibibytes on the amount of virtual memory (address space) used.
- -w n
-
Impose a limit of
n
kibibytes on the amount of swap space used.
As far as
ulimit
is concerned, a block is 512 bytes.
-
umask
[-S
]
[mask
]
-
- Display or set the file permission creation mask, or umask (see
umask(2)).
If the
-S
option is used, the mask displayed or set is symbolic; otherwise, it is an
octal number.
Symbolic masks are like those used by
chmod(1).
When used, they describe what permissions may be made available (as opposed to
octal masks in which a set bit means the corresponding bit is to be cleared).
For example,
``ug=rwx,o=''
sets the mask so files will not be readable, writable, or executable by
``others''
and is equivalent (on most systems) to the octal mask
``007''
-
unalias
[-adt
]
[name ...
]
-
- The aliases for the given names are removed.
If the
-a
option is used, all aliases are removed.
If the
-t
or
-d
options are used, the indicated operations are carried out on tracked or
directory aliases, respectively.
-
unset
[-fv
]
parameter ...
-
- Unset the named parameters
Po -v
the default
Pc or functions
(-f
)
With
parameter [*]
attributes are kept, only values are unset.
The exit status is non-zero if any of the parameters have the read-only
attribute set, zero otherwise.
- wait [job ...
]
-
Wait for the specified job(s) to finish.
The exit status of
wait
is that of the last specified job; if the last job is killed by a signal, the
exit status is 128 + the number of the signal (see
kill -l exit-status
above); if the last specified job can't be found (because it never existed, or
had already finished), the exit status of
wait
is 127.
See
Sx Job control
below for the format of
job
wait
will return if a signal for which a trap has been set is received, or if a
SIGHUP
SIGINT
or
SIGQUIT
signal is received.
If no jobs are specified,
wait
waits for all currently running jobs (if any) to finish and exits with a zero
status.
If job monitoring is enabled, the completion status of jobs is printed
(this is not the case when jobs are explicitly specified).
-
whence
[-pv
]
[name ...
]
-
- For each
name
the type of command is listed (reserved word, built-in, alias,
function, tracked alias, or executable).
If the
-p
option is used, a path search is performed even if
name
is a reserved word, alias, etc.
Without the
-v
option,
whence
is similar to
command -v
except that
whence
will find reserved words and won't print aliases as alias commands.
With the
-v
option,
whence
is the same as
command -V
Note that for
whence
the
-p
option does not affect the search path used, as it does for
command
If the type of one or more of the names could not be determined, the exit
status is non-zero.
Job control
Job control refers to the shell's ability to monitor and control jobs which
are processes or groups of processes created for commands or pipelines.
At a minimum, the shell keeps track of the status of the background (i.e.
asynchronous) jobs that currently exist; this information can be displayed
using the
jobs
commands.
If job control is fully enabled (using
set -m
or
set -o monitor )
as it is for interactive shells, the processes of a job are placed in their
own process group.
Foreground jobs can be stopped by typing the suspend
character from the terminal (normally ^Z), jobs can be restarted in either the
foreground or background using the
fg
and
bg
commands, and the state of the terminal is saved or restored when a foreground
job is stopped or restarted, respectively.
Note that only commands that create processes (e.g. asynchronous commands,
subshell commands, and non-built-in, non-function commands) can be stopped;
commands like
read
cannot be.
When a job is created, it is assigned a job number.
For interactive shells, this number is printed inside
``[..]''
followed by the process IDs of the processes in the job when an asynchronous
command is run.
A job may be referred to in the
bg
fg
jobs
kill
and
wait
commands either by the process ID of the last process in the command pipeline
(as stored in the
$!
parameter) or by prefixing the job number with a percent
sign
(`%'
)
Other percent sequences can also be used to refer to jobs:
- %+ | %% |
-
The most recently stopped job, or, if there are no stopped jobs, the oldest
running job.
- %-
-
The job that would be the
%+
job if the latter did not exist.
- % n
-
The job with job number
n
- %? string
-
The job with its command containing the string
string
(an error occurs if multiple jobs are matched).
- % string
-
The job with its command starting with the string
string
(an error occurs if multiple jobs are matched).
When a job changes state (e.g. a background job finishes or foreground job is
stopped), the shell prints the following status information:
where...
- number
-
is the job number of the job;
- flag
-
is the
`+'
or
`-'
character if the job is the
%+
or
%-
job, respectively, or space if it is neither;
- status
-
indicates the current state of the job and can be:
- Done [number
]
-
The job exited.
number
is the exit status of the job which is omitted if the status is zero.
- Running
-
The job has neither stopped nor exited (note that running does not necessarily
mean consuming CPU time ---
the process could be blocked waiting for some event).
- Stopped [signal
]
-
The job was stopped by the indicated
signal
(if no signal is given, the job was stopped by
SIGTSTP )
- signal-description [``core dumped''
]
-
The job was killed by a signal (e.g. memory fault, hangup); use
kill -l
for a list of signal descriptions.
The
``core dumped''
message indicates the process created a core file.
- command
-
is the command that created the process.
If there are multiple processes in
the job, each process will have a line showing its
command
and possibly its
status
if it is different from the status of the previous process.
When an attempt is made to exit the shell while there are jobs in the stopped
state, the shell warns the user that there are stopped jobs and does not exit.
If another attempt is immediately made to exit the shell, the stopped jobs are
sent a
SIGHUP
signal and the shell exits.
Similarly, if the
nohup
option is not set and there are running jobs when an attempt is made to exit
a login shell, the shell warns the user and does not exit.
If another attempt
is immediately made to exit the shell, the running jobs are sent a
SIGHUP
signal and the shell exits.
Interactive input line editing
The shell supports three modes of reading command lines from a
tty(4)
in an interactive session, controlled by the
emacs
gmacs
and
vi
options (at most one of these can be set at once).
The default is
emacs
Editing modes can be set explicitly using the
set
built-in.
If none of these options are enabled,
the shell simply reads lines using the normal
tty(4)
driver.
If the
emacs
or
gmacs
option is set, the shell allows emacs-like editing of the command; similarly,
if the
vi
option is set, the shell allows vi-like editing of the command.
These modes are described in detail in the following sections.
In these editing modes, if a line is longer than the screen width (see the
COLUMNS
parameter),
a
`>'
`+'
,
or
`<'
character
is displayed in the last column indicating that there are more
characters after, before and after, or before the current position,
respectively.
The line is scrolled horizontally as necessary.
Completed lines are pushed into the history, unless they begin with an
IFS octet or IFS white space, or are the same as the previous line.
Emacs editing mode
When the
emacs
option is set, interactive input line editing is enabled.
Warning: This mode is
slightly different from the emacs mode in the original Korn shell.
In this mode, various editing commands
(typically bound to one or more control characters) cause immediate actions
without waiting for a newline.
Several editing commands are bound to particular
control characters when the shell is invoked; these bindings can be changed
using the
bind
command.
The following is a list of available editing commands.
Each description starts with the name of the command,
suffixed with a colon;
an
[n
]
(if the command can be prefixed with a count); and any keys the command is
bound to by default, written using caret notation
e.g. the ASCII ESC character is written as ^[.
These control sequences are not case sensitive.
A count prefix for a command is entered using the sequence
^[ n
where
n
is a sequence of 1 or more digits.
Unless otherwise specified, if a count is
omitted, it defaults to 1.
Note that editing command names are used only with the
bind
command.
Furthermore, many editing commands are useful only on terminals with
a visible cursor.
The default bindings were chosen to resemble corresponding
Emacs key bindings.
The user's
tty(4)
characters (e.g.
ERASE
are bound to
reasonable substitutes and override the default bindings.
- abort: ^C, ^G
-
Abort the current command, empty the line buffer and
set the exit state to interrupted.
- auto-insert: [n
]
-
Simply causes the character to appear as literal input.
Most ordinary characters are bound to this.
-
backward-char:
[n
]
^B , ^XD , ANSI-CurLeft
-
- Moves the cursor backward
n
characters.
-
backward-word:
[n
]
^[b , ANSI-Ctrl-CurLeft , ANSI-Alt-CurLeft
-
- Moves the cursor backward to the beginning of the word; words consist of
alphanumerics, underscore
(`_'
)
and dollar sign
(`$'
)
characters.
- beginning-of-history: ^[<
-
Moves to the beginning of the history.
- beginning-of-line: ^A, ANSI-Home
-
Moves the cursor to the beginning of the edited input line.
-
capitalise-word:
[n
]
^[C , ^[c
-
- Uppercase the first character in the next
n
words, leaving the cursor past the end of the last word.
- clear-screen: ^[^L
-
Prints a compile-time configurable sequence to clear the screen and home
the cursor, redraws the entire prompt and the currently edited input line.
The default sequence works for almost all standard terminals.
- comment: ^[#
-
If the current line does not begin with a comment character, one is added at
the beginning of the line and the line is entered (as if return had been
pressed); otherwise, the existing comment characters are removed and the cursor
is placed at the beginning of the line.
- complete: ^[^[
-
Automatically completes as much as is unique of the command name or the file
name containing the cursor.
If the entire remaining command or file name is
unique, a space is printed after its completion, unless it is a directory name
in which case
`/'
is appended.
If there is no command or file name with the current partial word
as its prefix, a bell character is output (usually causing a beep to be
sounded).
- complete-command: ^X^[
-
Automatically completes as much as is unique of the command name having the
partial word up to the cursor as its prefix, as in the
complete
command above.
- complete-file: ^[^X
-
Automatically completes as much as is unique of the file name having the
partial word up to the cursor as its prefix, as in the
complete
command described above.
- complete-list: ^I, ^[=
-
Complete as much as is possible of the current word,
and list the possible completions for it.
If only one completion is possible,
match as in the
complete
command above.
Note that ^I is usually generated by the TAB (tabulator) key.
-
delete-char-backward:
[n
]
ERASE , ^? , ^H
-
- Deletes
n
characters before the cursor.
-
delete-char-forward:
[n
]
ANSI-Del
-
- Deletes
n
characters after the cursor.
-
delete-word-backward:
[n
]
WERASE , ^[^? , ^[^H , ^[h
-
- Deletes
n
words before the cursor.
-
delete-word-forward:
[n
]
^[d
-
- Deletes characters after the cursor up to the end of
n
words.
-
down-history:
[n
]
^N , ^XB , ANSI-CurDown
-
- Scrolls the history buffer forward
n
lines (later).
Each input line originally starts just after the last entry
in the history buffer, so
down-history
is not useful until either
search-history
search-history-up
or
up-history
has been performed.
-
downcase-word:
[n
]
^[L , ^[l
-
- Lowercases the next
n
words.
-
edit-line:
[n
]
^Xe
-
- Edit line
n
or the current line, if not specified, interactively.
The actual command executed is
fc -e ${VISUAL:-${EDITOR:-vi}} n
- end-of-history: ^[>
-
Moves to the end of the history.
- end-of-line: ^E, ANSI-End
-
Moves the cursor to the end of the input line.
- eot: ^_
-
Acts as an end-of-file; this is useful because edit-mode input disables
normal terminal input canonicalization.
-
eot-or-delete:
[n
]
^D
-
- Acts as
eot
if alone on a line; otherwise acts as
delete-char-forward
- error: (not bound)
-
Error (ring the bell).
- exchange-point-and-mark: ^X^X
-
Places the cursor where the mark is and sets the mark to where the cursor was.
- expand-file: ^[*
-
Appends a
`*'
to the current word and replaces the word with the result of performing file
globbing on the word.
If no files match the pattern, the bell is rung.
-
forward-char:
[n
]
^F , ^XC , ANSI-CurRight
-
- Moves the cursor forward
n
characters.
-
forward-word:
[n
]
^[f , ANSI-Ctrl-CurRight , ANSI-Alt-CurRight
-
- Moves the cursor forward to the end of the
n th
word.
-
goto-history:
[n
]
^[g
-
- Goes to history number
n
- kill-line: KILL
-
Deletes the entire input line.
- kill-region: ^W
-
Deletes the input between the cursor and the mark.
-
kill-to-eol:
[n
]
^K
-
- Deletes the input from the cursor to the end of the line if
n
is not specified; otherwise deletes characters between the cursor and column
n
- list: ^[?
-
Prints a sorted, columnated list of command names or file names (if any) that
can complete the partial word containing the cursor.
Directory names have
`/'
appended to them.
- list-command: ^X?
-
Prints a sorted, columnated list of command names (if any) that can complete
the partial word containing the cursor.
- list-file: ^X^Y
-
Prints a sorted, columnated list of file names (if any) that can complete the
partial word containing the cursor.
File type indicators are appended as described under
list
above.
- newline: ^J , ^M
-
Causes the current input line to be processed by the shell.
The current cursor position may be anywhere on the line.
- newline-and-next: ^O
-
Causes the current input line to be processed by the shell, and the next line
from history becomes the current line.
This is only useful after an
up-history
search-history
or
search-history-up
- no-op: QUIT
-
This does nothing.
- prefix-1: ^[
-
Introduces a 2-character command sequence.
- prefix-2: ^X , ^[[ , ^[O
-
Introduces a 2-character command sequence.
-
prev-hist-word:
[n
]
^[. , ^[_
-
- The last word, or, if given, the
n th
word (zero-based) of the previous (on repeated execution, second-last,
third-last, etc.) command is inserted at the cursor.
Use of this editing command trashes the mark.
- quote: ^^ , ^V
-
The following character is taken literally rather than as an editing command.
- redraw: ^L
-
Reprints the last line of the prompt string and the current input line
on a new line.
-
search-character-backward:
[n
]
^[^]
-
- Search backward in the current line for the
n th
occurrence of the next character typed.
-
search-character-forward:
[n
]
^]
-
- Search forward in the current line for the
n th
occurrence of the next character typed.
- search-history: ^R
-
Enter incremental search mode.
The internal history list is searched
backwards for commands matching the input.
An initial
`^'
in the search string anchors the search.
The escape key will leave search mode.
Other commands, including sequences of escape as
prefix-1
followed by a
prefix-1
or
prefix-2
key will be executed after leaving search mode.
The
abort (^G)
command will restore the input line before search started.
Successive
search-history
commands continue searching backward to the next previous occurrence of the
pattern.
The history buffer retains only a finite number of lines; the oldest
are discarded as necessary.
- search-history-up: ANSI-PgUp Search backwards through the history buffer for commands whose beginning match
-
the portion of the input line before the cursor.
When used on an empty line, this has the same effect as
up-history
- search-history-down: ANSI-PgDn Search forwards through the history buffer for commands whose beginning match
-
the portion of the input line before the cursor.
When used on an empty line, this has the same effect as
down-history
This is only useful after an
up-history
search-history
or
search-history-up
- set-mark-command: ^[ Aq space
-
Set the mark at the cursor position.
- transpose-chars: ^T
-
If at the end of line, or if the
gmacs
option is set, this exchanges the two previous characters; otherwise, it
exchanges the previous and current characters and moves the cursor one
character to the right.
-
up-history:
[n
]
^P , ^XA , ANSI-CurUp
-
- Scrolls the history buffer backward
n
lines (earlier).
-
upcase-word:
[n
]
^[U , ^[u
-
- Uppercase the next
n
words.
- version: ^[^V
-
Display the version of
mksh
The current edit buffer is restored as soon as a key is pressed.
The restoring keypress is processed, unless it is a space.
- yank: ^Y
-
Inserts the most recently killed text string at the current cursor position.
- yank-pop: ^[y
-
Immediately after a
yank
replaces the inserted text string with the next previously killed text string.
Vi editing mode
Note:
The vi command-line editing mode is orphaned, yet still functional.
It is 8-bit clean but specifically does not support UTF-8 or MBCS.
The vi command-line editor in
has basically the same commands as the
vi(1)
editor with the following exceptions:
-
You start out in insert mode.
-
There are file name and command completion commands:
=, \, *, ^X, ^E, ^F, and, optionally,
Aq tab
and
Aq esc .
-
The
_
command is different (in
mksh
it is the last argument command; in
vi(1)
it goes to the start of the current line).
-
The
/
and
G
commands move in the opposite direction to the
j
command.
-
Commands which don't make sense in a single line editor are not available
(e.g. screen movement commands and
ex(1)Ns-style
colon
(:
)
commands).
Like
vi(1),
there are two modes:
``insert''
mode and
``command''
mode.
In insert mode, most characters are simply put in the buffer at the
current cursor position as they are typed; however, some characters are
treated specially.
In particular, the following characters are taken from current
tty(4)
settings
(see
stty(1))
and have their usual meaning (normal values are in parentheses): kill (^U),
erase (^?), werase (^W), eof (^D), intr (^C), and quit (^\).
In addition to
the above, the following characters are also treated specially in insert mode:
- ^E
-
Command and file name enumeration (see below).
- ^F
-
Command and file name completion (see below).
If used twice in a row, the
list of possible completions is displayed; if used a third time, the completion
is undone.
- ^H
-
Erases previous character.
- ^J | ^M
-
End of line.
The current line is read, parsed, and executed by the shell.
- ^V
-
Literal next.
The next character typed is not treated specially (can be used
to insert the characters being described here).
- ^X
-
Command and file name expansion (see below).
- Aq esc
-
Puts the editor in command mode (see below).
- Aq tab
-
Optional file name and command completion (see
^F
above), enabled with
set -o vi-tabcomplete
In command mode, each character is interpreted as a command.
Characters that
don't correspond to commands, are illegal combinations of commands, or are
commands that can't be carried out, all cause beeps.
In the following command descriptions, an
[n
]
indicates the command may be prefixed by a number (e.g.
10l
moves right 10 characters); if no number prefix is used,
n
is assumed to be 1 unless otherwise specified.
The term
``current position''
refers to the position between the cursor and the character preceding the
cursor.
A
``word''
is a sequence of letters, digits, and underscore characters or a sequence of
non-letter, non-digit, non-underscore, and non-whitespace characters (e.g.
``ab2*&^''
contains two words) and a
``big-word''
is a sequence of non-whitespace characters.
Special
vi commands:
The following commands are not in, or are different from, the normal vi file
editor:
-
[n _
]
-
- Insert a space followed by the
n th
big-word from the last command in the history at the current position and enter
insert mode; if
n
is not specified, the last word is inserted.
- #
-
Insert the comment character
(`#'
)
at the start of the current line and return the line to the shell (equivalent
to
I#^J )
-
[n g
]
-
- Like
G
except if
n
is not specified, it goes to the most recent remembered line.
-
[n v
]
-
- Edit line
n
using the
vi(1)
editor; if
n
is not specified, the current line is edited.
The actual command executed is
fc -e ${VISUAL:-${EDITOR:-vi}} n
- * and ^X
-
Command or file name expansion is applied to the current big-word (with an
appended
`*'
if the word contains no file globbing characters) --- the big-word is replaced
with the resulting words.
If the current big-word is the first on the line
or follows one of the characters
`;'
,
`|'
`&'
,
`('
,
or
`)'
,
and does not contain a slash
(`/'
)
then command expansion is done; otherwise file name expansion is done.
Command expansion will match the big-word against all aliases, functions, and
built-in commands as well as any executable files found by searching the
directories in the
PATH
parameter.
File name expansion matches the big-word against the files in the
current directory.
After expansion, the cursor is placed just past the last
word and the editor is in insert mode.
-
[n \
]
[n ^F
]
[n Aq tab
]
and
[n Aq esc
]
-
- Command/file name completion.
Replace the current big-word with the
longest unique match obtained after performing command and file name expansion.
Aq tab
is only recognised if the
vi-tabcomplete
option is set, while
Aq esc
is only recognised if the
vi-esccomplete
option is set (see
set -o )
If
n
is specified, the
n th
possible completion is selected (as reported by the command/file name
enumeration command).
- = and ^E
-
Command/file name enumeration.
List all the commands or files that match the current big-word.
- ^V
-
Display the version of
mksh
The current edit buffer is restored as soon as a key is pressed.
The restoring keypress is ignored.
- @ c
-
Macro expansion.
Execute the commands found in the alias
c
Intra-line movement commands:
-
[n h and
]
[n ^H
]
-
- Move left
n
characters.
-
[n l and
]
[n Aq space
]
-
- Move right
n
characters.
- 0
-
Move to column 0.
- ^
-
Move to the first non-whitespace character.
-
[n |
]
-
- Move to column
n
- $
-
Move to the last character.
-
[n b
]
-
- Move back
n
words.
-
[n B
]
-
- Move back
n
big-words.
-
[n e
]
-
- Move forward to the end of the word,
n
times.
-
[n E
]
-
- Move forward to the end of the big-word,
n
times.
-
[n w
]
-
- Move forward
n
words.
-
[n W
]
-
- Move forward
n
big-words.
- %
-
Find match.
The editor looks forward for the nearest parenthesis, bracket, or
brace and then moves the cursor to the matching parenthesis, bracket, or brace.
-
[n f c
]
-
- Move forward to the
n th
occurrence of the character
c
-
[n F c
]
-
- Move backward to the
n th
occurrence of the character
c
-
[n t c
]
-
- Move forward to just before the
n th
occurrence of the character
c
-
[n T c
]
-
- Move backward to just before the
n th
occurrence of the character
c
-
[n ;
]
-
- Repeats the last
f , F , t
or
T
command.
-
[n ,
]
-
- Repeats the last
f , F , t
or
T
command, but moves in the opposite direction.
Inter-line movement commands:
-
[n j
]
[n +
]
and
[n ^N
]
-
- Move to the
n th
next line in the history.
-
[n k
]
[n -
]
and
[n ^P
]
-
- Move to the
n th
previous line in the history.
-
[n G
]
-
- Move to line
n
in the history; if
n
is not specified, the number of the first remembered line is used.
-
[n g
]
-
- Like
G
except if
n
is not specified, it goes to the most recent remembered line.
-
[n / string
]
-
- Search backward through the history for the
n th
line containing
string
if
string
starts with
`^'
,
the remainder of the string must appear at the start of the history line for
it to match.
-
[n ? string
]
-
- Same as
/
except it searches forward through the history.
-
[n n
]
-
- Search for the
n th
occurrence of the last search string;
the direction of the search is the same as the last search.
-
[n N
]
-
- Search for the
n th
occurrence of the last search string;
the direction of the search is the opposite of the last search.
- ANSI-CurUp Take the characters from the beginning of the line to the current
-
cursor position as search string and do a backwards history search
for lines beginning with this string; keep the cursor position.
This works only in insert mode and keeps it enabled.
Edit commands
-
[n a
]
-
- Append text
n
times; goes into insert mode just after the current position.
The append is
only replicated if command mode is re-entered i.e.
Aq esc
is used.
-
[n A
]
-
- Same as
a
except it appends at the end of the line.
-
[n i
]
-
- Insert text
n
times; goes into insert mode at the current position.
The insertion is only
replicated if command mode is re-entered i.e.
Aq esc
is used.
-
[n I
]
-
- Same as
i
except the insertion is done just before the first non-blank character.
-
[n s
]
-
- Substitute the next
n
characters (i.e. delete the characters and go into insert mode).
- S
-
Substitute whole line.
All characters from the first non-blank character to the
end of the line are deleted and insert mode is entered.
-
[n c move-cmd
]
-
- Change from the current position to the position resulting from
n move-cmd s
(i.e. delete the indicated region and go into insert mode); if
move-cmd
is
c
the line starting from the first non-blank character is changed.
- C
-
Change from the current position to the end of the line (i.e. delete to the
end of the line and go into insert mode).
-
[n x
]
-
- Delete the next
n
characters.
-
[n X
]
-
- Delete the previous
n
characters.
- D
-
Delete to the end of the line.
-
[n d move-cmd
]
-
- Delete from the current position to the position resulting from
n move-cmd s
move-cmd
is a movement command (see above) or
d
in which case the current line is deleted.
-
[n r c
]
-
- Replace the next
n
characters with the character
c
-
[n R
]
-
- Replace.
Enter insert mode but overwrite existing characters instead of
inserting before existing characters.
The replacement is repeated
n
times.
-
[n ~
]
-
- Change the case of the next
n
characters.
-
[n y move-cmd
]
-
- Yank from the current position to the position resulting from
n move-cmd s
into the yank buffer; if
move-cmd
is
y
the whole line is yanked.
- Y
-
Yank from the current position to the end of the line.
-
[n p
]
-
- Paste the contents of the yank buffer just after the current position,
n
times.
-
[n P
]
-
- Same as
p
except the buffer is pasted at the current position.
Miscellaneous vi commands
- ^J and ^M
-
The current line is read, parsed, and executed by the shell.
- ^L and ^R
-
Redraw the current line.
-
[n .
]
-
- Redo the last edit command
n
times.
- u
-
Undo the last edit command.
- U
-
Undo all changes that have been made to the current line.
- intr and quit
-
The interrupt and quit terminal characters cause the current line to be
deleted and a new prompt to be printed.
FILES
- ~/.mkshrc
-
User mkshrc profile (non-privileged interactive shells); see
Sx Startup files.
The location can be changed at compile time (for embedded systems);
AOSP Android builds use
/system/etc/mkshrc
- ~/.profile
-
User profile (non-privileged login shells); see
Sx Startup files
near the top of this manual.
- /etc/profile
-
System profile (login shells); see
Sx Startup files.
- /etc/shells
-
Shell database.
- /etc/suid_profile
-
Suid profile (privileged shells); see
Sx Startup files.
Note: On Android,
/system/etc/
contains the system and suid profile.
SEE ALSO
awk(1),
cat(1),
ed(1),
getopt(1),
sed(1),
sh(1),
stty(1),
dup(2),
execve(2),
getgid(2),
getuid(2),
mknod(2),
mkfifo(2),
open(2),
pipe(2),
rename(2),
wait(2),
getopt(3),
nl_langinfo3,
setlocale(3),
signal(3),
system(3),
tty(4),
shells(5),
environ(7),
script(7),
utf-87,
mknod(8)
http://docsrv.sco.com:507/en/man/html.C/sh.C.html
https://www.mirbsd.org/ksh-chan.htm
-
Morris Bolsky
"The KornShell Command and Programming Language"
1989
"xvi + 356 pages"
"ISBN 978-0-13-516972-8 (0-13-516972-0)"
-
Morris I. Bolsky
David G. Korn
"The New KornShell Command and Programming Language (2nd Edition)"
1995
"xvi + 400 pages"
"ISBN 978-0-13-182700-4 (0-13-182700-6)"
-
Stephen G. Kochan
Patrick H. Wood
"\*(tNUNIX\*(sP Shell Programming"
"3rd Edition"
2003
"xiii + 437 pages"
"ISBN 978-0-672-32490-1 (0-672-32490-3)"
-
"IEEE Inc."
"\*(tNIEEE\*(sP Standard for Information Technology --- Portable Operating System Interface (POSIX)"
"Part 2: Shell and Utilities"
1993
"xvii + 1195 pages"
"ISBN 978-1-55937-255-8 (1-55937-255-9)"
-
Bill Rosenblatt
"Learning the Korn Shell"
1993
"360 pages"
"ISBN 978-1-56592-054-5 (1-56592-054-6)"
-
Bill Rosenblatt
Arnold Robbins
"Learning the Korn Shell, Second Edition"
2002
"432 pages"
"ISBN 978-0-596-00195-7 (0-596-00195-9)"
-
Barry Rosenberg
"KornShell Programming Tutorial"
1991
"xxi + 324 pages"
"ISBN 978-0-201-56324-5 (0-201-56324-X)"
AUTHORS
An -nosplit
The MirBSD Korn Shell
is developed by
An Thorsten Glaser Aq
tg@mirbsd.org
and currently maintained as part of The MirOS Project.
This shell is based on the public domain 7th edition Bourne shell clone by
An Charles Forsyth ,
who kindly agreed to, in countries where the Public Domain status of the work
may not be valid, grant a copyright licence to the general public to deal in
the work without restriction and permission to sublicence derivates under the
terms of any (OSI approved) Open Source licence,
and parts of the BRL shell by
An Doug A. Gwyn ,
An Doug Kingston ,
An Ron Natalie ,
An Arnold Robbins ,
An Lou Salkind ,
and others.
The first release of
pdksh
was created by
An Eric Gisin ,
and it was subsequently maintained by
An John R. MacMillan Aq Mt change!
john@sq.sq.com ,
An Simon J. Gerraty Aq Mt
sjg@zen.void.oz.au ,
and
An Michael Rendell Aq Mt
michael@cs.mun.ca .
The effort of several projects, such as Debian and OpenBSD, and other
contributors including our users, to improve the shell is appreciated.
See the documentation, CVS, and web site for details.
The BSD daemon is Copyright © Marshall Kirk McKusick.
The complete legalese is at:
https://www.mirbsd.org/TaC-mksh.txt
CAVEATS
only supports the Unicode BMP (Basic Multilingual Plane).
has a different scope model from
AT&T System
ksh
which leads to subtile differences in semantics for identical builtins.
This can cause issues with a
nameref
to suddenly point to a local variable by accident; fixing this is hard.
The parts of a pipeline, like below, are executed in subshells.
Thus, variable assignments inside them are not visible in the
surrounding execution environment.
Use co-processes instead.
foo | bar | read baz # will not change $baz
foo | bar |& read -p baz # will, however, do so
mksh
provides a consistent set of 32-bit integer arithmetics, both signed
and unsigned, with defined wraparound and sign of the result of a
remainder operation, even (defying POSIX) on 64-bit systems.
If you require 64-bit integer arithmetics, use
lksh (legacy mksh)
instead, but be aware that, in POSIX, it's legal for the OS to make
print $((2147483647 + 1))
delete all files on your system, as it's Undefined Behaviour.
BUGS
Suspending (using ^Z) pipelines like the one below will only suspend
the currently running part of the pipeline; in this example,
``fubar''
is immediately printed on suspension (but not later after an
fg )
$ /bin/sleep 666 && echo fubar
This document attempts to describe
mksh R50
and up,
compiled without any options impacting functionality, such as
MKSH_SMALL
when not called as
/bin/sh
which, on some systems only, enables
set -o sh
automatically (whose behaviour differs across targets),
for an operating environment supporting all of its advanced needs.
Please report bugs in
to the
MirOS
mailing list at
Aq miros-mksh@mirbsd.org
or in the
#!/bin/mksh
(or #ksh
)
IRC channel at
irc.freenode.net
(Port 6697 SSL, 6667 unencrypted)
or at:
https://launchpad.net/mksh
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- I'm an Android user, so what's mksh?
-
- Invocation
-
- Startup files
-
- Command syntax
-
- Quoting
-
- Backslash expansion
-
- Aliases
-
- Substitution
-
- Parameters
-
- Tilde expansion
-
- Brace expansion (alteration)
-
- File name patterns
-
- Input/output redirection
-
- Arithmetic expressions
-
- Co-processes
-
- Functions
-
- Command execution
-
- Job control
-
- Interactive input line editing
-
- Emacs editing mode
-
- Vi editing mode
-
- FILES
-
- SEE ALSO
-
- AUTHORS
-
- CAVEATS
-
- BUGS
-