groff_trace(7) Miscellaneous Information Manual groff_trace(7)
Name
groff_trace - macros for debugging GNU roff documents
Synopsis
groff -m trace [option ...] [file ...]
Description
trace is a macro package for the groff(7) document formatting system,
designed as an aid for debugging documents written in its language. It
issues a message to the standard error stream upon entry to and exit
from each macro call. This can ease the process of isolating errors in
macro definitions.
Activate the package by specifying the command-line option "-m trace"
to the formatter program (often groff(1)). You can achieve finer
control by including the macro file within the document; invoke the mso
request, as in ".mso trace.tmac". Only macros that are defined after
this invocation are traced. If the trace-full register is set to a
true value, as with the command-line option "-r trace-full=1", register
and string assignments, along with some other requests, are traced
also. If another macro package should be traced as well, specify it
after "-m trace" on the command line.
The macro file trace.tmac is unusual because it does not contain any
macros to be called by a user. Instead, groff's macro definition and
alteration facilities are wrapped such that they display diagnostic
messages.
Limitations
Because trace.tmac wraps the de request (and its cousins), macro
arguments are expanded one level more. This causes problems if an
argument uses four or more backslashes to delay interpretation of an
escape sequence. For example, the macro call
.foo \\\\n[bar]
normally passes "\\n[bar]" to macro "foo", but with de redefined, it
passes "\n[bar]" instead.
The solution to this problem is to use groff's \E escape sequence, an
escape character that is not interpreted in copy mode.
.foo \En[bar]
Examples
We will illustrate trace.tmac using the shell's "here document" feature
to supply groff with a document on the standard input stream. Since we
are interested only in diagnostic messages appearing on the standard
error stream, we discard the formatted output by redirecting the
standard output stream to /dev/null.
Observing nested macro calls
Macro calls can be nested, even with themselves. Tracing recurses
along with them; this feature can help to detangle complex call stacks.
$ cat <<EOF | groff -m trace > /dev/null
.de countdown
. nop \\$1
. nr count (\\$1 - 1)
. if \\n[count] .countdown \\n[count]
..
.countdown 3
blastoff
EOF
*** .de countdown
*** de trace enter: .countdown "3"
*** de trace enter: .countdown "2"
*** de trace enter: .countdown "1"
*** trace exit: .countdown "1"
*** trace exit: .countdown "2"
*** trace exit: .countdown "3"
Tracing with the mso request
Now let us activate tracing within the document, not with a command-
line option. We might do this when using a macro package like ms or
mom, where we may not want to be distracted by traces of macros we
didn't write.
$ cat <<EOF | groff -ms > /dev/null
.LP
This is my introductory paragraph.
.mso trace.tmac
.de Mymac
..
.Mymac
.PP
Let us review the existing literature.
EOF
*** .de Mymac
*** de trace enter: .Mymac
*** trace exit: .Mymac
As tracing was not yet active when the macros "LP" and "PP" were
defined (by s.tmac), their calls were not traced; contrast with the
macro "Mymac".
Files
/opt/local/share/groff/1.23.0/tmac/trace.tmac
implements the package.
Authors
trace.tmac was written by James Clark. This document was written by
Bernd Warken <groff-bernd.warken-72@web.de> and G. Branden Robinson
<g.branden.robinson@gmail.com>.
See also
Groff: The GNU Implementation of troff, by Trent A. Fisher and Werner
Lemberg, is the primary groff manual. You can browse it interactively
with "info groff".
groff(1)
gives an overview of the groff document formatting system.
troff(1)
supplies details of the -m command-line option.
groff_tmac(5)
offers a survey of groff macro packages.
groff(7)
is a reference manual for the groff language.
groff 1.23.0 2 July 2023 groff_trace(7)
groff 1.23.0 - Generated Fri Dec 22 19:37:36 CST 2023