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

# LEARN: weird -- the method has named parameters ... since v5.36

sub commits_for_month ($repo, $since, $until) {
  my $cmd = sprintf(
    q{git -C %s log --since="%s" --until="%s" --pretty=format:"%%s"},
    $repo, $since, $until
  );

  my @commits = `$cmd`;
  chomp @commits;

  return @commits;
}

1;

##</code><code>##

llegal character in prototype for main::commits_for_month : $repo, $since, $until at ./gitter.pl line 7.
Global symbol "$repo" requires explicit package name (did you forget to declare "my $repo"?) at ./gitter.pl line 10.
Global symbol "$since" requires explicit package name (did you forget to declare "my $since"?) at ./gitter.pl line 10.
Global symbol "$until" requires explicit package name (did you forget to declare "my $until"?) at ./gitter.pl line 11.
./gitter.pl had compilation errors.

##</code><code>##

This is perl 5, version 40, subversion 1 (v5.40.1) built for x86_64-linux-thread-multi
...

##</code><code>##

use v5.36; 

##</code><code>##

 perl -c ./gitter.pl
./gitter.pl syntax OK