use warnings;
use strict;
my $foo = shift || 12;
my $i = 2;
print "Is \`$foo' a two-digit number ... ";
#my $rc = ($foo =~ /^[0-9]{($i + 1)}$/) ? 'yes' : 'no';
my $rc = ($foo =~ /^[0-9]{$i}$/) ? 'yes' : 'no';
#my $rc = ($foo =~ /^[0-9]{2}$/) ? 'yes' : 'no';
print $rc,"\n";

__END__

Is `12' a two-digit number ... yes
[download]

Add re to your code to see what is happening under the hood:

use re 'debug';
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toolic,

i know i can merely do $i = 2, but i am wondering if it is possibly to instead not have to set/reset any variable, but instead calculate it using the ($n + 1) convention.

thanks for the use re 'debug' tip, never used that before.

It sounds like the OP wants to capture the number of occurrences entirely within the regex, something like:

$foo =~ m/[0-9]({\d+})/
print "$foo has $1 digit(s)";
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... if that were possible (it isn't). This would allow the counting match to be thrown in with a longer regex that is matching on other properties as well. This is probably possible through clever use of code evaluation (?{code}) and interpolation within the regex.

However, if all you need to do is count in the regex then you could use the 'goatse' operator:

my $length =()= $foo =~ /[0-9]/g;
print "$foo has $length digit(s)";
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Seems better than looping and incrementing, anyway.

FWIW:

>perl -wMstrict -le
"my $s = '123 234 3456789 3210 34567';
 ;;
 my @m = $s =~ m{ \b ((\d) (??{ qr{\d{$^N}} })) \b }xmsg;
 print qq{@m};
 ;;
 my $i = 2;
 @m = $s =~ m{ \b (??{ ++$i;  qr{\d{$i}}; }) \b }xmsg;
 print qq{@m};
"
234 2 3210 3
123 3456789
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okay, AnomalousMonk, this works:

# the original number of integers to test (will be one-upped)
my $i = 1; 

# the input string to be tested (a number)
my $foo = shift;

# see if the input string is a two-digit number
my $rc = ($foo =~ m{ \b (??{ ++$i; qr{\d{$i}}; }) \b }xmsg) ?'Y' :'N';
[download]

very clever...thanks.

... if that were possible (it isn't). This would allow the counting match to be thrown in with a longer regex that is matching on other properties as well. This is probably possible through clever use of code evaluation (?{code}) and interpolation within the regex.

that's actually kind of hoping for...a clever use of eval - but i couldn't figure that out. anyway, sounds like what i want is not possible, at least in a straight-forward fashion.

$num='36737';
$idx=0;
while($num=~m/[0-9]{$idx}/)
{
       $idx++;
}
$idx--; # adjusment to get correct answer
print "\n$num has $idx digits ";
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Is this what you wanted?

What's the bigger problem you are trying to solve? Kinda sounds like using a claw hammer to remove a tyre when you should be using a tyre iron.

I learned this here at PerlMonks: you can execute an expression inside a string or a regex pattern by wrapping it in @{[]}, like so:

#!/usr/bin/env perl
use Modern::Perl;

my $str = 'abc123efghijk';
my $i = 2;

if( $str =~ /(\d{@{[$i+1]}})/ ){
    say $1;
}
# output -> 123
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nice, aaron.

my $rc = ($foo =~ /^(\d{@{[$i+1]}})$/

always w/Perl, TIMTOWTDI...