#!/usr/bin/env perl
use strict;
my $line = 'not an exit statment';
print "line matched ! =~\n"      if (! $line =~ m/^\s*exit\s*$/i   );
print "line matched !(=~)\n"     if (! ($line =~ m/^\s*exit\s*$/i) );
print "line matched not =~ \n"   if (not $line =~ m/^\s*exit\s*$/i );
print "line matched if !~\n"     if ( $line !~ m/^\s*exit\s*$/i );
print "line matched unless =~\n" unless ($line =~ m/^\s*exit\s*$/i);
__END__
line matched !(=~)
line matched not =~
line matched if !~
line matched unless =~