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