GROFF_TRACE(7)         (9 September 2021)          GROFF_TRACE(7)

     NAME
          groff_trace - groff macro package trace.tmac

     SYNOPSIS
          [option ...] [input-file ...]

     DESCRIPTION
          The trace macro package of groff(1) can be a valuable tool
          for debugging documents written in the roff formatting lan-
          guage.  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 modi-
          fied 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 diag-
          nostic messages (standard error) on the terminal, the normal
          formatted output (standard output) is redirected to the nir-
          vana device /dev/null. The resulting diagnostic messages are
          displayed directly below the corresponding example.

        Command line option
          Example:

               sh# echo [aq].
               > .de test_macro
               > ..
               > .test_macro
               > .test_macro some dummy arguments

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               > [aq] | 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) [em] together with the argu-
          ments (if any).

        Nested macro calls
          Example:

               sh# echo [aq].
               > .de child
               > ..
               > .de parent
               > .child
               > ..
               > .parent
               > [aq] | 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 [aq].
               > .de before
               > ..
               > .mso trace.tmac
               > .de after
               > ..
               > .before
               > .after
               > .before
               > [aq] | groff > /dev/null

               *** de trace enter: .after
               *** trace exit: .after

          Here, the tracing is activated within the document, not by a

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          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 [oq]\\n[bar][cq] to macro [oq].foo[cq], but
          with the redefined .de request it passes [oq]\n[bar][cq]
          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

     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 [lq]info groff[rq].

          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)

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               A general description of groff macro packages.

          groff(7)
               A short reference for the groff formatting language.

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