Section: (1)
Updated: 2012-04-24
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prerex - interactive editor of prerequisite-chart descriptions  


prerex [ options ] [ basefile[.tex] [ chartfile[.tex] ] ]  


prerex is an interactive program for editing prerequisite-chart descriptions in the prerex(5) format. The user does not normally have to be familiar with details of the format. The editor supports add, remove, cut-and-paste, and edit operations on diagram elements, and vertical or horizontal shifts of a list of specified elements, all the elements in a rectangular region, or the entire diagram. The edited diagram may be saved, re-processed, and viewed in a PDF viewer, without exiting the editor. Alternatively, vprerex(1) will open a prerex(1) window and display the corresponding PDF file alongside.  


A prerequisite chart consists of several course boxes, linked by arrows. Courses are either half or full, and may be required or optional (or neither). Each course box contains a course code (upper left corner), a course title (lower half), and timetable information (upper right corner). An arrow is either a prerequisite (solid), a corequisite (dotted), or recommended (dashed). When a conventional arrow would be inappropriate, a mini course just above a target box may be used. A line of text may have been placed anywhere in the chart.

In some implementations of the prerex(5) format, (some) arrows may be curved and by default have non-zero curvature. The curvature of individual arrows may be edited using the prerex(1) editor. To modify the default curvature (or set it to zero), see prerex.sty(7).  


A conventional two-dimensional coordinate system is used to specify the locations of diagram elements; the origin (where x = 0 and y = 0) is at the lower-left corner of the diagram. For convenience, a coordinate grid is normally displayed in the background while a diagram is being edited.

The coordinates of a box, mini, or text-line are those of its centre point. An arrow is described by the coordinates of the centre points of its source and target boxes/minis/text-lines.

The notation x0,y0:x1,y1 denotes all the nodes (course boxes, minis, texts) in the rectangle whose northwest and southeast corners are at coordinates x0,y0 and x1,y1.  


If prerex is invoked on one existing file, a back-up copy is made of it, the x,y coordinate grid is turned on, the file is processed by using a system call to pdflatex(1), and then the user gets a command summary and an interactive prompt of the form

If no file argument is given on the command line, the user is prompted to supply a file name. In either case, if the file name provided does not have a .tex extension, .tex is appended to it.

If the file.tex file named does not already exist, a new "empty" chart file with that name is created, and then it is processed as above.

If a second filename is provided, the first filename is treated as the base file of a LaTeX document and the second as an included file that contains the chart environment to be edited. This allows more than one document to share an included chart file and allows more than one chart to be included in a single document.

The user may enter commands at the interactive command prompt as follows:

box x,y
edit a course box at x,y, if necessary, creating a new course box there
mini x,y
edit a mini at x,y, if necessary, creating a new mini there
text x,y
edit a text-line at x,y, if necessary, creating a new text-line there
arrow x0,y0,x1,y1
edit an arrow from x0,y0 to x1,y1, if necessary, creating a new such arrow
cut xi,yi ...
(temporarily) remove the box, mini, or text at xi,yi (including arrows into/out of the box/mini/text)
paste [x,y]
re-insert most recently cut but not yet pasted box, mini, or text at x,y (including arrows into/out of the box/mini/text), or at the original coordinates if x,y omitted
xchange x0,y0 x1,y1
exchange the box, mini or text at x0,y0 with that at x1,y1. This is implemented as a sequence of two cuts followed by two pastes to the same points.
delete [ x,y | x0,y0,x1,y1 | x0,y0:x1,y1 ] ...
remove the specified boxes, minis, texts, or arrows (including automatically all arrows into/out of each box/mini/text)
undo the most recent editing command (not already undone)
shift [-]s [ x,y | x0,y0:x1,y1 ] ...
move specified diagram elements x units right [left]; if no elements are specified, the whole diagram is shifted
raise [-]r [ x,y | x0,y0:x1,y1 ] ...
move specified diagram elements y units up [down]; if no elements are specified, the whole diagram is raised
write, !
save to the current chartfile.tex and process the chart by calling pdflatex(1) on the base file.
quit, exit, x, ^D
turn off the coordinate grid, restore write-access, save to the current chartfile.tex, process the base file and exit.
restore write access to chartfile.tex, execute shell command cmd, re-load and re-process the base file (in case the command changed anything), and remove write-access.
copy the current chartfile.tex to the back-up file .chartfile.tex; equivalent to !cp chartfile.tex .chartfile.tex
delete the current chartfile.tex and editing buffer, and replace them using the current back-up in .chartfile.tex.
grid [y/n]
turn on/off coordinate-grid background
help, ?
print a command summary

After most editing commands, the editing buffer is automatically saved to chartfile.tex and the basefile is processed; the cut and paste commands are exceptions: saving and processing take place only when all outstanding cuts have been pasted. Saving and processing can be forced by using the write (or !) command, or suppressed for all commands (except write and !) by appending a ";" to the command immediately prior to entering it. To exit the editor without saving to the current chartfile.tex, use quit; (.i.e., quit followed by a semi-colon) or a similar combination. Starting in Version 3.8, ^C and other interrupts result in the editing buffer being saved to chartfile.tex before the editor is exited.  


output program name and version number, and quit
output usage summary and quit


The main difference between mini and text is in the maximum lengths for the text displayed; the latter allows a full line of text, not merely a course code. Also a text-line does not have an associated URI (when the grid is off). The text "line" may actually be displayed as a paragraph by using a LaTeX \parbox.

To save the current state of chartfile.tex, use Backup or a comparable shell command. A history list of interpreted commands is maintained and is accessible using the up-arrow key.

If processing of the chart fails, prerex will attempt to display the LaTeX error message from the log file. The chart file can be fixed using a conventional text editor or LaTeX-oriented editor. LaTeX processing should fail only if there is an initial problem or if ill-formed LaTeX markup has been inserted into a text field.

Any (non-empty) prefix of a command suffices; for example, q, qu, or qui may be used instead of quit. Some of the commands will begin a dialogue with the user in order to fill in or modify properties; the prompts should be self-explanatory.

Since version 5.5, prerex no longer automatically calls a PDF viewer (because it may be embedded in an instance of vprerex(1) which already provides a PDF display). If prerex is being used by itself, a PDF viewer may be invoked using the !cmd shell-escape mechanism. Also, prerex no longer interacts with the user until a PDF file is available; this is for use with vprerex(1). For example, if the .tex file is initially read-only, prerex aborts.  


A LaTeX style file prerex.sty(7) that implements the macro calls defined by the prerex(5) format must be available to [pdf]latex(1) to process the chart file. Before any editing is allowed, chartfile.tex is copied to .chartfile.tex as a backup.  


The most convenient viewing program to use with prerex is one like gv(1), gsview(1), kghostview(1), kpdf(1) or okular(1) that may be configured to "watch" the pdf file and re-load the display automatically when the file changes. evince(1) has a Reload button and xpdf(1) supports re-loading using the keystroke "R", but re-loading is much less convenient with acroread(1) and gpdf(1), which may have to be re-started.

Recent versions of some PDF viewers show the URIs of hyperlinks in a tooltip or in the status bar; this mechanism is used by some implementations of prerex.sty(7) to allow display of the coordinates of a box, mini, text-line, or arrow when the mouse hovers over it (while the coordinate grid is on and the relevant chart file is presumably being edited).

The prerex package at has source code for vprerex(1), a GUI front-end for prerex which is prerex-enabled.  


prerex analyzes chart files without using TeX; thus, macro calls are not expanded, and anything in the chart file before or after the (first) \begin{chart} ... \end{chart} environment is ignored (but preserved) by the editor. Lines that begin with "%" within the chart environment are preserved but other comments within the chart environment are not preserved and may interfere with command parsing.

From version 5.6, prerex no longer supports the latex -> dvips -> ps2pdf toolchain as an option.  


R. D. Tennent (  


prerex uses the editline(3) library if available and the GNU readline(3) and history(3) libraries otherwise.  


acroread(1), evince(1), gpdf(1), gsview(1), gv(1), kghostview(1), kpdf(1), okular(1), pdflatex(1), prerex(5), prerex.sty(7), previewer(1), vprerex(1), xpdf(1).