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   libexpect    ( 3 )

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Отладка (Debugging)

While I consider the library to be easy to use, I think that the
       standalone expect program is much, much, easier to use than
       working with the C compiler and its usual edit, compile, debug
       cycle.  Unlike typical C programs, most of the debugging isn't
       getting the C compiler to accept your programs - rather, it is
       getting the dialogue correct.  Also, translating scripts from
       expect to C is usually not necessary.  For example, the speed of
       interactive dialogues is virtually never an issue.  So please try
       the standalone 'expect' program first.  I suspect it is a more
       appropriate solution for most people than the library.

       Nonetheless, if you feel compelled to debug in C, here are some
       tools to help you.

       extern int exp_is_debugging;
       extern FILE *exp_debugfile;

       While expect dialogues seem very intuitive, trying to codify them
       in a program can reveal many surprises in a program's interface.
       Therefore a variety of debugging aids are available.  They are
       controlled by the above variables, all 0 by default.

       Debugging information internal to expect is sent to stderr when
       exp_is_debugging is non-zero.  The debugging information includes
       every character received, and every attempt made to match the
       current input against the patterns.  In addition, non-printable
       characters are translated to a printable form.  For example, a
       control-C appears as a caret followed by a C.  If exp_logfile is
       non-zero, this information is also written to that stream.

       If exp_debugfile is non-zero, all normal and debugging
       information is written to that stream, regardless of the value of
       exp_is_debugging.