#! /usr/bin/perl -w

use strict;

my $want_next_line = 0;
my $on = '';

while( <DATA> ) {
  chomp;          # never use chop
  s/\s*#.*$//;    # discard comments
  next unless $_; # go to next line if nothing left

  if( /^on (.*)$/i ) {
    $on = $1;
  }
  elsif( $want_next_line ) {
    $on .= $_;
  }
  $want_next_line = $on =~ /,$/ ? 1 : 0;
}
$on =~  s/\s//g;
print "\$on = $on\n";

__DATA__
INPUT FILE =
# comment
# comment
ON Mon, Tues,
Fri,
Sat
# comment
other stuff