# NAME Devel::TraceRun - Shows all the function calls and returns in a Perl program # PROJECT STATUS [![CPAN version](https://badge.fury.io/pl/Devel-TraceRun.svg)](https://metacpan.org/pod/Devel::TraceRun) # SYNOPSIS $ perl -d -d:TraceRun -S yourscript # DESCRIPTION Figuring out a large system's workings is hard. Figuring out why it's not working, and where it's going wrong, is even harder. This tool produces an indented list of all function calls with parameters (in a very very concise format) and return values (ditto). It aims to minimise diffs between runs of a program that are doing the same thing, so that differences stand out. The output is on `STDOUT` currently. That may become overridable in due course. ## Example This code (from the test - `Thing::func` calls `Thing::func2` which returns "2nd retval"): use Thing; my $f = sub { Thing::func() }; Thing::func([2]); # void my @r = Thing::func([2]); my @r2 = $f->("very long string", 2, bless {}, 'Thing'); run with: perl -d -d:TraceRun script.pl produces on perl 5.8 - 5.14 (output is slightly different from 5.16, and again from 5.28): main::(script.pl:1)() return() Thing::func(ARRAY) Thing::func2() return() return() Thing::func(ARRAY) Thing::func2() return(2nd retval) return(2nd retval) main entry(very long ,2,Thing) Thing::func() Thing::func2() return(2nd retval) return(2nd retval) return(2nd retval) Note that in void context, nothing is returned. Also note the `very long string` is truncated to (currently) 10 characters, array- and hash-refs are printed just as `ARRAY` and `HASH`, and objects as their classname. There is currently no way to change what is printed. One thing that would increase homogeneity across runs would be a way to specify for certain function-names, which inputs or outputs to mask. Obvious examples where this would help are functions that return the current time, or a random number, or the port number of an incoming IP connection. Another source of output variation is the change in Perl 5.18 to randomise the order hash-keys are returned in. You can overcome this for tracing purposes by setting the environment variable `PERL_HASH_SEED` to 0, which also has the effect of setting `PERL_PERTURB_KEYS` to 0. ## How it works As may be discerned from the command line, it uses Perl's debugging functionality. However, unlike the normal use of that, it is entirely non-interactive. Instead, it replaces `DB::DB` with a no-op, and uses the `DB::sub` hook to report function entries and returns. These reports are indented (currently hardcoded to two spaces), nested according to stack depth. It is intended to be completely obvious what everything means. # SEE ALSO [perldebguts](https://metacpan.org/pod/perldebguts) # AUTHOR Ed J # COPYRIGHT AND LICENSE This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.