#!/usr/bin/perl
use strict;use warnings;

while (my $line=<DATA>) {
    $line=~s/(?<!\\)#.*//;
    print $line;
    }

__DATA__
\#Not a comment
#Comment
\#Not a comment  #But this is a comment
arbitrary text   #Comment
arbitrary text   \#Not a comment
arbitrary text   \#Not a comment  #But this is a comment
arbitrary text   #Comment         \#This is part of the comment