It might not work every time, but it works most of the times:

#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

use Data::Dumper;
local $Data::Dumper::Deparse = 1;

sub secret {
    'Just Another Perl Hacker,'
}

for my $symbol (keys %main::) {
    my $def = do { no strict;
                   Dumper(${'main::'}{$symbol}) };
    say "$symbol => $def" if $def =~ /sub/;
}
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Update: Or, instead of using a regex to identify subs:

#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

use Data::Dumper;
local $Data::Dumper::Deparse = 1;

sub secret {
    'Just Another Perl Hacker,'
}

for my $symbol (keys %main::) {
    my $def = do { no strict;
                   *{"main::$symbol"}{CODE} };
    say "$symbol => ", Dumper $def if $def;
}
[download]