#!/usr/bin/perl5 -w
use strict;

my ($is_okay, $value);

sub return_okay {
   my $test_string = shift;
   my $private_result = ($test_string =~ /myregex/);
   return ($private_result);
}

sub return_okay2 {            # concise version
   return ($_[0] =~ /myregex/);
}

sub modify_okay {             # but see WARNING below
   # Called as: modify_okay($string, $result_flag)
   $_[1] = ($_[0] =~ /myregex/);
}

my @vals = qw(abcdefg myregex tuvwxyz);

print "Using a return value:\n";
foreach $value (@vals) {
   $is_okay = return_okay2($value);      ###
   if ($is_okay) {
      print "$value is okay.\n";
   }
   else {
      print "$value is not okay.\n";
   }
}

print "\nUsing a modified value:\n";
foreach $value (@vals) {
   modify_okay($value, $is_okay);        ###
   if ($is_okay) {
      print "$value is okay.\n";
   }
   else {
      print "$value is not okay.\n";
   }
}

# WARNING: the modify method can blow up on you
# Notice that the following line causes a fatal error 
# because of the attempt to modify a constant:

modify_okay("some string", 1);

print "And this never prints\n";

##</code><code>##

for (@vals) {
   my $qualifier = return_okay2($_) ? "" : " not";
   print "$_ is$qualifier okay.\n";
}

##</code><code>##

print map "$_ is ".(return_okay2($_)?'':' not')." okay\n", @vals;