Anonymous: The following code I used,
but if I go for more than 6 digits its getting fail,

Whats meant by "more/less than six digits"?

Would this: "123456abcde" be acceptable?
Or this one: "abc123456def" ? Or only this: "123456" ?

If *not*, you need anchored match, ^ => "line start", $ => "line end"
otherwise, you can use lookaround assertions (?...)

 ... 
 my $d = shift; # $ARGV[0]
 
 if( $d =~ /(?<!\d)\d{6}(?!\d)/ ) {  print "Exact match (lookaround)\n
+" }
 else { print "Not Correct\n" }
 
 if( $d =~ /^\d{6}$/ ) {  print "Exact match (anchored)\n" }
 else { print "Not Correct\n" }
 ...
[download]

Regards

mwa