sub foo {
  print STDERR "Entering sub foo(@_)\n";
 # Do something
  print STDERR "Exiting sub foo: return value $bar\n";
  return $bar;
}
[download]

Failing all of that, I will offer the following two toys. They are not perfect - they may not catch everything - but they have worked quite well for me.

First Toy

#!/usr/bin/perl -w
# usage: $0 filename [optional output file]
# If the output file is not specified, it will print to STDOUT

use strict;

my $outp;

open FILE, $ARGV[0] or die "A grim and horrible death: $!";
if ( defined( $ARGV[1] ) ) {
    open OUTP, ">$ARGV[1]" or die "Couldn't write: $!";
    $outp = \*OUTP;
}
else {
    $outp = \*STDOUT;
}

my ( %calls, $name, @context );
#---
# First parsing phase is to try to gather all the return codes togethe
+r,
# keyed by the function name
#---
while ( <FILE> ) {
     next if /^\s*#/;
    next if /^\s*$/;
    last if /__END__/;

    $name = $1 if /^sub (\w+)/;

    #---
    # Push the context and get next line if possible
    #---
    if ( /^\s*return (\$?[\w->:]+) (if .+)[;{]$/ ||
        /^\s*return (\$?[\w->:]+) (unless .+)[;{]$/ ) {
        my ( $code, $context ) = ( $1, $2 );

        chomp $context;
        $context =~ s/^\s+//;

        push @{$calls{$name}{$code}}, $context;
        next;
    }

    if ( /(.+){$/ ) {
        chomp;
        s/^\s+//;
        push @context, $_ 
    }

    pop  @context if ( /}$/ );

    push(@{$calls{$name}{$1}}, $context[-1]),next if ( /\s*return (\$?
+[\w->:{}]+
)/ );
}
close FILE;

for my $name ( sort keys %calls ) {
    for my $rc ( sort keys %{$calls{$name}} ) {
        print $outp "$rc when:\n\t";
        local $" = "\n\t";
        print $outp "@{$calls{$name}{$rc}}\n";
    }
}
[download]

Second Toy

#!/usr/bin/perl -w
use strict;

die "$0 <source> <target> ..." unless @ARGV > 1;
my %keyword = ();

my ( $source, @targets ) = @ARGV;

my $package = '';
#---
# Try to extract the keywords, precompile the regex and store
#---
open SRC, $source or die "Couldn't open $source : $!";
while( <SRC> ) {
    $package = $1 if ( ! $package && /^package\s+(.+);/ );
    next unless ( /^sub\s+(.+){\s*$/ );

    my $name;
    $name = $1;
    next if ( substr($name,0,1) eq "_" );

    $name =~ s/\s+$//;
    $keyword{$name} = qr/([\w:{}]+)->$name/;
}
close SRC;

for my $file ( @targets ) {
    my ( $line );

    open FILE, $file or die "Couldn't open $file : $!";

    LINE:
        while( $line = <FILE> ) {
            next LINE if ( $line =~ /^\s*#/ || $line =~ /^\s*$/ );
            last LINE if $line =~ /__END__/;


            for ( keys %keyword ) {
                my $regex = $keyword{$_};
                if ( $line =~ /$regex/ ) {
                    my $starts_at = $.;
                    my $lpack = $1 || '';

                    next LINE if ( $file eq $source ) && ( $line =~ /^
+sub/ );
                    next LINE if ( $line =~ /Usage/ );
                    next LINE if ( $lpack =~ /::/ && $lpack ne $packag
+e );

                    while( $line !~ /;/ && ! eof(FILE) ) {
                        $line .= <FILE>;
                        next LINE if $line =~ /^EOF/m;
                    }
                    $line =~ s/^\s*//;
                    printf "%s (%d) %s", uc $file, $starts_at, $line;
                    next LINE;
                }
            }
        }
    #LINE
    close FILE;
}
[download]

Hm. This might be too low-level, but you might want to have a look a the following:

• Devel::GraphVizProf
• Devel::Trace
• Devel::TraceFuncs
• Devel::DProf
• B::Graph
• B::Tree
• GraphViz

Christian Lemburg
Brainbench MVP for Perl
http://www.brainbench.com

You might want to use Deparse to show you the reduced syntax, this will produce slightly prettier output, which might help you a little.

# bad perl
print $foo; s/dog/cat/gm; m%foo%;
FOO: for ($foo) { /dog/ && do {last FOO}; /cat/ && do {$dog = 'rabbit'
+};}
exit(0) or die "wooot?";
[download]

When run through Deparse:

bash-2.03$ perl -MO=Deparse badperl.pl
badperl.pl syntax OK
print $foo;
s/dog/cat/gm;
/foo/;
FOO: foreach $_ ($foo) {
    if (/dog/) {
        last FOO;
    }
    if (/cat/) {
        $dog = 'rabbit';
    }
}
die 'wooot?' unless exit 0;
[download]

As you can see, some bits get clearer, while others get a little more murky, but it's a useful tool.