In Perl, how can I test if a string is a palindrome?

Question

I'm attempting to write a Perl program to determine if a 7 character user input is a palindrome.

Without using any array, string, or reverse functions.

Desired output:

    Enter in a 7 character item: 1111111
    PALINDROME!

Or

    Enter in a 7 character item: 1234567
    NOT A PALINDROME!

This is what I have so far:

print "Enter in a 7 character item: \n";
my ($a, $b, $c, $d, $e, $f, $g);
chomp ($a=<>); chomp ($b=<>); chomp ($c=<>); chomp ($d=<>);
chomp ($e=<>); chomp ($f=<>); chomp ($g=<>);
if ($a~~$g && $b~~$g && $c~~$e){
    print "PALINDROME!\n";
}
else{
    print "NOT A PALINDROME! \n";
}

Unfortunately, this is giving me this result:

    Enter in a 7 character item:
    1
    1
    1
    1
    1
    1
    1
    PALINDROME!

If anyone has suggestions, that would be greatly appreciated.

I look forward to hearing your input. Thank you!

Answer 1

That looks correct to me, after all 1111111 is a palindrome!

However, the smart match operator isn't a very useful thing, and you want to test for string equality here, so use eq instead of ~~ .

Even better I would suggest that you allow the user to enter an entire string, so

chomp(my $str = <>);

if ( $str eq reverse($str) ) {
     print "PALINDROME!\n";
}
else {
     print "NOT A PALINDROME! \n";
}

Answer 2

Without using reverse :

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

my ($word) = @ARGV;

my @chars = split //, $word;
my $palindrome = 1;
for (0..@chars/2-1) {
   $palindrome = $chars[$_] eq $chars[-($_+1)]
      or last;
}

print "$word ".($palindrome ? "is" : "isn't")." a palindrome\n";

Usage:

script word

Answer 3

Changing

$b~~$g to $b~~$f might also help.

Answer 4

no reverse used, but regex (and recursion).

 sub palyndromeP{
     my $s=shift;
     if (length($s)<2) {return 1}        
     if ($s !~ /^(.)(.*)\1$/) {return 0}
     return palyndromeP($2);
 }