in reply to Re: perl equiv regex for C strtol
in thread perl equiv regex for C strtol

Thanks for the advice.
I have been writing code since 1968, actually the first few lines prior to that. I had a series back in the 70's in Kilobaud magazine, and spent 15 years in the Unix environment. I have used regular expressions, and even felt quite confident when it came to knowing how I was going to do something before I started. Unlike playing the piano, however I have had to re-learn how to use every time I stop for a few years.
Now I am 65, and am lucky I remember which side of the bed to get out of
I will however learn again, I just need a little help this evening.
As always, I have found it on PerlMonks!
Thanks Again - L.

br

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Re^3: perl equiv regex for C strtol
by Anonymous Monk on May 01, 2012 at 06:36 UTC

    Hi

    Regexp::English 

    #!/usr/bin/perl --
use Regexp::English;
print Regexp::English ->new
    ->remember
    ->multiple
    ->digit, "\n";
__END__
(?^:((?:\d+)))

    [download]

    Becomes 

    my( @numbers ) = $str -~  m{ (\d+) }gx;

    [download]
    /g means global match (match them all), x means ignore literal white space in pattern

    YAPE::Regex::Explain can explain a lot of these (though it could use some updating) 

    use YAPE::Regex::Explain;
print YAPE::Regex::Explain->new(
qr{ (\d+) }x,
)->explain;
__END__
The regular expression:

(?x-ims: (\d+) )

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?x-ims:                 group, but do not capture (disregarding
                         whitespace and comments) (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n):
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    \d+                      digits (0-9) (1 or more times (matching
                             the most amount possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

    [download]

    See also Visual (perl/Tk) regex tweaking utility (its like a living cheatsheet). See also perlrequick

    And see Regexp::Common 

    $ perl -MRegexp::Common -e " print $RE{num}{int} "
(?:(?:[+-]?)(?:[0123456789]+))

    [download]

    And the magic of /x revealed 

    #!/usr/bin/perl --
use strict; use warnings;
my $REint = qr{
#---------------------------------------------------------------------
+-
  (?:                  #    group, but do not capture:
#---------------------------------------------------------------------
+-
    (?:                #      group, but do not capture:
#---------------------------------------------------------------------
+-
      [+-]?            #        any character of: '+', '-' (optional
                       #        (matching the most amount possible))
#---------------------------------------------------------------------
+-
    )                  #      end of grouping
#---------------------------------------------------------------------
+-
    (?:                #      group, but do not capture:
#---------------------------------------------------------------------
+-
      [0123456789]+    #        any character of: '0', '1', '2', '3',
                       #        '4', '5', '6', '7', '8', '9' (1 or
                       #        more times (matching the most amount
                       #        possible))
#---------------------------------------------------------------------
+-
    )                  #      end of grouping
#---------------------------------------------------------------------
+-
  )                    #    end of grouping
#---------------------------------------------------------------------
+-
}x; # end of qr

print "$_\n" for "1 plus 1 is 2" =~ m/$REint/g
__END__
1
1
2

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