NAME

       groff_trace - groff macro package trace.tmac

SYNOPSIS

       groff -m trace [option ...] [input-file ...]

DESCRIPTION

       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.

EXAMPLES

       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.

   Command line option
       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).

   Nested macro calls
       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.

   Activating with .mso
       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.

PROBLEMS

       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]

FILES

       The  trace  macros  are  kept  in  the  file trace.tmac located in the tmac directory; see
       groff_tmac(5) for details.

ENVIRONMENT

       GROFF_TMAC_PATH
              A colon-separated list of additional tmac directories in which to search for  macro
              files; see groff_tmac(5) for details.

AUTHORS

       The  trace  macro packages was written by James Clark.  This document was written by Bernd
       Warken ⟨groff-bernd.warken-72@web.de⟩.

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)
              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.