How can I run through a Perl program step by step?

Question

I have a Perl program written by someone else. When I run it, it silently exits without writing anything to the logfile. Is there a way I can run this Perl program step by step, line by line by the interpreter and thus get to see where it terminates?

Answer 1

Yes, there is the Perl debugger which you can invoke with perl -d.

Documentation can be found in perldoc perldebug and perldoc perldebtut.

Probably the most useful commands would be:

s                 - step into current line.
n                 - step over current line.
r                 - step out of current function.
p <expr>          - print the expression.
b <line|subnm>    - sets a breakpoint
T                 - produce a stack trace.
c [<line|subnm>]  - continue running with optional one-time breakpoint.
h                 - help (for other commands).

Answer 2

Hachi has the answer. Use the Perl debugger by running perl with the -d flag. For information on how to use the debugger past starting it, see the Perl Debugging Tutorial.