Hello roho,

Change $1 to \1 within the regex:

use strict;
use warnings;

my @txt = ('cc', 'cz');

for (@txt)
{
    if (m/^(.)\1$/)
    {
        print "True   \$_ = |$_|   \$1 = |$1|\n";
    }
    else
    {
        print "False  \$_ = |$_|   \$1 = |$1|\n";
    }
}
[download]

Output:

14:13 >perl 2092.SoPW.pl
True   $_ = |cc|   $1 = |c|
False  $_ = |cz|   $1 = |c|

14:14 >
[download]

As you can see:

• warnings are gone
• the closing $ is OK now
• $1 is no longer the empty string on match fail, but is rather the captured character “c”.

See e.g. Capture groups.

Hope that helps,