G'day cavac,

This does/doesn't match as per your example:

qr{^\s*[^#]*\s*sub}
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Quick test:

#!/usr/bin/env perl

use v5.26;

my $re = qr{^\s*[^#]*\s*sub};

my (@match, @no_match);

while (<DATA>) {
    if (/$re/) {
        push @match, $_;
    }
    else {
        push @no_match, $_;
    }
}

say '*** Matched:';
print for @match;
say '*** Not Matched:';
print for @no_match;

__DATA__
should match these:
sub hello {
    sub hello {

should not match these:
#sub hello {
#    sub hello {
    # sub hello {
    #     sub hello {
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Output:

*** Matched:
sub hello {
    sub hello {
*** Not Matched:
should match these:

should not match these:
#sub hello {
#    sub hello {
    # sub hello {
    #     sub hello {
[download]

I guess the next question is: are there any examples you want to match that do not start m{ ^ \s* sub \b }x? If not, then you have your answer; if there are, those are the tricky cases we'd need to see.

I just took a quick look at one of my codebases and found 558 matches for that pattern; 503 of them were normal sub declarations all matching m{ ^ \s* sub \s+ (\w+) \s* \{ }x, the rest were anonymous sub references not matching that pattern. Of matches against m{ \b sub \b }x elsewhere in any line, almost all were anonymous sub references (the remaining 2 or 3 were comments or $sub variables).

So that pattern would work for me, would it work for you?