Right, because if you silently produce bad results from bad data it's not your fault you sloppily didn't do any validation . . .

Doing it right with error checking and using the right tools from the toolbox requires much less code and is more robust (and actually produces correct results since you don't get a chance to bollux up the ordering of the multiple tests your approach requires).

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

my @tests;
BEGIN {
  @tests = ( 
[ '10.1.2.31',  '10.1.2.30', '10.1.2.45' , 1 ],
[ '10.1.2.255', '9.1.2.30',  '11.1.2.45' , 1 ],
[ '10.1.2.255', '10.1.1.30', '10.1.3.45' , 1 ],
[ '10.1.2.255', '10.1.2.30', '10.1.2.45' , 0 ],
[ '10.1.2.255', '10.1.2.30', '10.1.2.255', 1  ],
[ '10.1.2.29',  '10.1.2.30', '10.1.2.255', 0  ],
[ '10.1.2.30',  '10.1.2.30', '10.1.2.255', 1  ],
);
}

use Test::More tests => 14+1;

for my $check ( @tests ) {
  my( $test, $start, $end, $result ) = @{ $check };
  my $desc = "$test " . ( $result ? "is" : "isn't" ) . " between $star
+t and $end";
  is( ip_in_range( $test, $start, $end), $result, $desc );
  is( cmp_ips( $test, $start, $end), $result, $desc );
}
    
is( ip_in_range( "I R BAD IP", "10.2.1.1", "10.2.1.10" ), undef, "Bad 
+IP Check" );

## 13 lines
use Socket qw( inet_aton );

sub ip_in_range {
    my ( $test, $start, $end ) = map {
        unpack( "N", inet_aton($_) )
            or do { warn "Invalid IP: $_\n"; return undef }
    } @_;

    return 0 if $test < $start;
    return 0 if $test > $end;
    return 1;
}

## 27 lines
sub cmp_ips{
   my @r;
   my @t = quadify(shift);
   my @s = quadify(shift);
   my @e = quadify(shift);

   ($t[0] == $s[0] && $t[0] == $e[0]) ? $r[0] = 1 : $r[0] = 0;
   ($t[1] == $s[1] && $t[1] == $e[1]) ? $r[1] = 1 : $r[1] = 0;
   ($t[2] == $s[2] && $t[2] == $e[2]) ? $r[2] = 1 : $r[2] = 0;
   ($t[3] == $s[3] && $t[3] == $e[3]) ? $r[3] = 1 : $r[3] = 0;

   return 1 if $t[0]*$t[1]*$t[2]*$t[3] == 1;

   return 1 if ($r[0] == 0 && ($t[0] >= $s[0] && $t[0] <= $e[0]) );
   return 1 if ($r[1] == 0 && ($t[1] >= $s[1] && $t[1] <= $e[1]) );
   return 1 if ($r[2] == 0 && ($t[2] >= $s[2] && $t[2] <= $e[2]) );
   return 1 if ($r[3] == 0 && ($t[3] >= $s[3] && $t[3] <= $e[3]) );

   return 0;
}

sub quadify{
  my $ip = shift;
   $ip =~ /^(\d+)\.(\d+)\.(\d+)\.(\d+)$/;
   return ($1,$2,$3,$4);
}

__END__
1..15
ok 1 - 10.1.2.31 is between 10.1.2.30 and 10.1.2.45
ok 2 - 10.1.2.31 is between 10.1.2.30 and 10.1.2.45
ok 3 - 10.1.2.255 is between 9.1.2.30 and 11.1.2.45
ok 4 - 10.1.2.255 is between 9.1.2.30 and 11.1.2.45
ok 5 - 10.1.2.255 is between 10.1.1.30 and 10.1.3.45
ok 6 - 10.1.2.255 is between 10.1.1.30 and 10.1.3.45
ok 7 - 10.1.2.255 isn't between 10.1.2.30 and 10.1.2.45
not ok 8 - 10.1.2.255 isn't between 10.1.2.30 and 10.1.2.45
#   Failed test '10.1.2.255 isn't between 10.1.2.30 and 10.1.2.45'
#   in /Users/fletch/snit at line 26.
#          got: '1'
#     expected: '0'
ok 9 - 10.1.2.255 is between 10.1.2.30 and 10.1.2.255
ok 10 - 10.1.2.255 is between 10.1.2.30 and 10.1.2.255
ok 11 - 10.1.2.29 isn't between 10.1.2.30 and 10.1.2.255
not ok 12 - 10.1.2.29 isn't between 10.1.2.30 and 10.1.2.255
#   Failed test '10.1.2.29 isn't between 10.1.2.30 and 10.1.2.255'
#   in /Users/fletch/snit at line 26.
#          got: '1'
#     expected: '0'
ok 13 - 10.1.2.30 is between 10.1.2.30 and 10.1.2.255
ok 14 - 10.1.2.30 is between 10.1.2.30 and 10.1.2.255
Use of uninitialized value in unpack at /Users/fletch/snit line 34.
Invalid IP: I R BAD IP
ok 15 - Bad IP Check
# Looks like you failed 2 tests of 15.
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