When i give it user input it matches the regex

print "Please enter the string ";
chomp($string=<STDIN>);
$regex= "^\d{4,4}[A-Z0-9]$ ";
if ($string =~ m!($regex)!g) 
{                
  print 'match';
    print "$regex";
  } 
else 
{
  print 'no match';
    print "$regex";
  }
  
  
[download]

It matches the regex in this case but when the input is a text file it fails to recognize any patterns

Show us some sample data that fails and some test code. If the problem is real you shouldn't need more than a few lines of data and a few lines of code to reproduce the problem.

Are you sure the pattern you want to match is at the start of the line? Could it be that you are reading the entire file into a string and are then trying to match against that string? If so you probably need to use the m (multiple line match) switch. Consider:

use strict;
use warnings;

my $str = <<TEXT;
First line
1234X
last line
TEXT

print "Matched\n"       if $str =~ /^\d{4,4}[A-Z0-9]$/;
print "Multi-matched\n" if $str =~ /^\d{4,4}[A-Z0-9]$/m;
[download]

prints:

Multi-matched
[download]

Yes have to search in multilines so i used /m but it still does not give any matches. I think the problem is with ^ and $ as only regex having these identifiers are giving me problem rest ase working fine such as for email validation

/[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?/g

The ^ and $ around the regex mean that it only matches a whole string. If you want to search for matches inside a string, leave out those anchors.

See perlretut for more details.

how do i substitute ^ and $ in my regex

Well, what semantics do you want?

If you just want to remove the restriction that the regex has to match the whole string, remove them.

Perl 6 - second systems done right