#!/usr/bin/perl
my $string=('data12.csv');
$string=~ s/\D//g;
$string = 0 if $string eq '';
print "$string\n";
[download]

Or even:

c:\@Work\Perl\monks>perl -wMstrict -le
"my $string = 'data.csv';
 $string =~ s/\D//g;
 $string ||= 0;
 print qq{'$string'};
"
'0'
[download]

---

Give a man a fish:  <%-(-(-(-<

hum... I wonder why didn't I think about this way? Thank you, works great!

Here's one way using a subroutine and the ternary operator. It will return $str if $str isn't empty, and if it is, returns 0.

#!/usr/bin/perl

use warnings;
use strict;

my $string = "data.csv";

my $return = num($string);

sub num {
    my $str = shift;
    $str =~ s/\D//g;

    return $str ? $str : 0;
}
[download]

Or without the sub:

my $str = "data.csv";
$str =~ s/\D//g;
$str = $str ? $str : 0;

print $str;
[download]

-stevieb

UPDATE: Sound enough code (and can be adapted (below) to OP's needs), but NOT a complete answer to OP's question, which I mis-read.

Use the inverse of your regex, namely:

$string=~ s/\d//g;

like this without having to add additional tests to deal with strings which have no numbers:

C:\>perl -E "my $string=('data12.csv');$string=~ s/\d//g;say $string;
data.csv

C:\>perl -E "my $string=('data.csv');$string=~ s/\d//g;say $string;"
data.csv
[download]

Illustration of adaptation (see the parent, Re: How to remove non-numbers from string)

#! /usr/bin/perl
use 5.018;
use strict;
use warnings;

my @strings=('data.csv', 'data12.csv', '123data.csv', 'data000.csv', '
+data.csv0', '123.', '1data2.csv');

for my $string(@strings) {    
    if ( $string =~ /(\d+)/g ) {
        my $revised = $1;   
        say "\$string was:\t$string;\t RESULT: $revised (from Ln 11)";
    } else {                   # i.e., if there are no digits
        my $revised = "0";
        say "\$string was:\t$string; \t RESULT: $revised (from Ln 14)"
+;
    }
}

=head

C:\>1131407.pl
$string was:    data.csv;        RESULT: 0 (from Ln 14)
$string was:    data12.csv;      RESULT: 12 (from Ln 11)
$string was:    123data.csv;     RESULT: 123 (from Ln 11)
$string was:    data000.csv;     RESULT: 000 (from Ln 11)
$string was:    data.csv0;       RESULT: 0 (from Ln 11)     #problem1
$string was:    123.;    RESULT: 123 (from Ln 11)
$string was:    1data2.csv;      RESULT: 1 (from Ln 11)     #problem2
[download]

• # problem1: How do you want to distingush this (or 'data0.csv') from an element with no zeros?
• # problem2: ... and what about an element with more than one set of digits, such as "1data2.csv"



++$anecdote ne $data (nor does it eq code)

Problematic with warnings enabled:

c:\@Work\Perl\monks>perl -wMstrict -le
"my $string = 'data.csv';
 $string =~ s/\D//g;
 $string += 0;
 print qq{'$string'};
"
Argument "" isn't numeric in addition (+) at -e line 1.
'0'
[download]

---

Give a man a fish:  <%-(-(-(-<

Yes, I have just encountered this very same problem!

Great idea; thank you!