YAPE::Regex::Explain is a handy tool to help you understand regular expressions: 
use strict;
use warnings;
use YAPE::Regex::Explain;

print YAPE::Regex::Explain->new('^\d[1]{1}$')->explain();

__END__

The regular expression:

(?-imsx:^\d[1]{1}$)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  ^                        the beginning of the string
----------------------------------------------------------------------
  \d                       digits (0-9)
----------------------------------------------------------------------
  [1]{1}                   any character of: '1' (1 times)
----------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

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In reply to Re: REGEX Match Single Digit by toolic
in thread REGEX Match Single Digit by spickles

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