File: gawk.info,  Node: Limitations,  Next: Debugging Summary,  Prev: Readline Support,  Up: Debugger

14.5 Limitations
================

We hope you find the 'gawk' debugger useful and enjoyable to work with,
but as with any program, especially in its early releases, it still has
some limitations.  A few that it's worth being aware of are:

   * At this point, the debugger does not give a detailed explanation of
     what you did wrong when you type in something it doesn't like.
     Rather, it just responds 'syntax error'.  When you do figure out
     what your mistake was, though, you'll feel like a real guru.

   * If you perused the dump of opcodes in *note Miscellaneous Debugger
     Commands:: (or if you are already familiar with 'gawk' internals),
     you will realize that much of the internal manipulation of data in
     'gawk', as in many interpreters, is done on a stack.  'Op_push',
     'Op_pop', and the like are the "bread and butter" of most 'gawk'
     code.

     Unfortunately, as of now, the 'gawk' debugger does not allow you to
     examine the stack's contents.  That is, the intermediate results of
     expression evaluation are on the stack, but cannot be printed.
     Rather, only variables that are defined in the program can be
     printed.  Of course, a workaround for this is to use more explicit
     variables at the debugging stage and then change back to obscure,
     perhaps more optimal code later.

   * There is no way to look "inside" the process of compiling regular
     expressions to see if you got it right.  As an 'awk' programmer,
     you are expected to know the meaning of '/[^[:alnum:][:blank:]]/'.

   * The 'gawk' debugger is designed to be used by running a program
     (with all its parameters) on the command line, as described in
     *note Debugger Invocation::.  There is no way (as of now) to attach
     or "break into" a running program.  This seems reasonable for a
     language that is used mainly for quickly executing, short programs.

   * The 'gawk' debugger only accepts source code supplied with the '-f'
     option.  If you have a shell script that provides an 'awk' program
     as a command line parameter, and you need to use the debugger, you
     can write the script to a temporary file, and use that as the
     program, with the '-f' option.  This might look like this:

          cat << \EOF > /tmp/script.$$
          ...                                  Your program here
          EOF
          gawk -D -f /tmp/script.$$
          rm /tmp/script.$$