groff_trace - groff macro package trace.tmac
[
option ...] [
input-file ...]
The
trace macro package of
groff(1) can be a valuable tool for
debugging documents written in the roff formatting language. A call stack
trace is protocolled on standard error, this is, a diagnostic message is
emitted on entering and exiting of a macro call. This greatly eases to track
down an error in some macro.
This tracing process is activated by specifying the groff or troff command-line
option
-m trace. This works also with the
groffer(1)
viewer program. A finer control can be obtained by including the macro file
within the document by the groff macro call
.mso trace.tmac.
Only macros that are defined after this line are traced.
If the command-line option
-r trace-full=1 is given (or if this
register is set in the document), number and string register assignments
together with some other requests are traced also.
If some other macro package should be traced as well it must be specified 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, the existing macro definition and
appending facilities are modified such that they display diagnostic messages.
In the following examples, a roff fragment is fed into groff via standard input.
As we are only interested in the diagnostic messages (standard error) on the
terminal, the normal formatted output (standard output) is redirected to the
nirvana device
/dev/null. The resulting diagnostic messages are
displayed directly below the corresponding example.
Example:
sh# echo '.
> .de test_macro
> ..
> .test_macro
> .test_macro some dummy arguments
> ' | groff -m trace > /dev/null
*** .de test_macro
*** de trace enter: .test_macro
*** trace exit: .test_macro
*** de trace enter: .test_macro "some" "dummy" "arguments"
*** trace exit: .test_macro "some" "dummy" "arguments"
The entry and the exit of each macro call is displayed on the terminal (standard
output) — together with the arguments (if any).
Example:
sh# echo '.
> .de child
> ..
> .de parent
> .child
> ..
> .parent
> ' | groff -m trace > /dev/null
*** .de child
*** .de parent
*** de trace enter: .parent
*** de trace enter: .child
*** trace exit: .child
*** trace exit: .parent
This shows that macro calls can be nested. This powerful feature can help to
tack down quite complex call stacks.
Example:
sh# echo '.
> .de before
> ..
> .mso trace.tmac
> .de after
> ..
> .before
> .after
> .before
> ' | groff > /dev/null
*** de trace enter: .after
*** trace exit: .after
Here, the tracing is activated within the document, not by a command-line
option. As tracing was not active when macro
before was defined, no
call of this macro is protocolled; on the other hand, the macro
after
is fully protocolled.
Because
trace.tmac wraps the
.de request (and its cousins), macro
arguments are expanded one level more. This causes problems if an argument
contains four backslashes or more to prevent too early expansion of the
backslash. For example, this macro call
-
.foo \\\\n[bar]
normally passes ‘\\n[bar]’ to macro ‘.foo’, but with
the redefined
.de request it passes ‘\n[bar]’ instead.
The solution to this problem is to use groff's
\E escape which is an
escape character not interpreted in copy mode, for example
-
.foo \En[bar]
The
trace macros are kept in the file
trace.tmac located in the
tmac directory; see
groff_tmac(5) for details.
- GROFF_TMAC_PATH
- A colon-separated list of additional tmac directories in
which to search for macro files; see groff_tmac(5) for
details.
The
trace macro packages was written by James Clark. This document was
written by
Bernd
Warken
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)
- An overview of the groff system.
-
troff(1)
- For details on option -m.
-
groffer(1)
- A viewer program for all kinds of roff documents.
-
groff_tmac(5)
- A general description of groff macro packages.
-
groff(7)
- A short reference for the groff formatting language.