Using "perl -d" on the script shouldn't be a problem, and there's every good reason to use it as a first resort, so long as you establish some good places to put breakpoints before you start execution. Let me embellish Ovid's advice a bit; if you're on a system with an "egrep" command, just do:

egrep -n 'eval|format' your_script.pl
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or if you don't have egrep (well, get it -- the gnu version is available for MS Windows), you could use a command-line perl script to the same effect:

perl -ne 'print "$. $_" if (/eval|format/)' your_script.pl
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Anyplace where "format" follows closely after "eval", use the line number of the "eval" to set a breakpoint in the debugger (using the "b" command).

When using the debugger, I find it helpful to have the script also loaded in a text editor that allows going to specific line numbers easily.

If this is a cgi script, you'll either need to set $ENV{QUERY_STRING} to some suitable value before starting execution, or else you may want to "enhance" the script a bit so it can get the query_string args from ARGV if $ENV{QUERY_STRING} happens to be empty. UPDATEHaving just seen that you have multiple source files to work through, exend the egrep to all source files, and also find the names of subs or objects in the "main" script that reference the other sources, and put breakpoints on those names, so that when you "step" into those calls, you can then set line-number based breakpoints within those other source files. Okay, so there's more prep work before actually starting execution in the debugger, but it's still likely to be the shortest path.