#!perl

use strict;
use warnings;

while (<DATA>) {
   chomp; # get rid of pesky newlines
   if(is_integer_string($_)){
       print "$_ is a valid integer string\n";
   }
   else {
       print "$_ isn't a valid integer string\n";
   }
 }
sub is_integer_string {

   # a valid integer is any amount of white space, followed
   # by an optional sign, followed by at least one digit,
   # followed by any amount of white space

   return $_[0] =~ /^\s*[\+\-]?\d+\s*$/;
}
__DATA__
1
1234
 +1234
 -1234
 A
 1234+
+ 1234