$s = '00111100110';;

$s =~ s[(1+)]['2' x length $1]e;;

print $s;;
00222200110
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Thanks!

as I was testing the code I realize, the code that I am using is not matching the longest string of 1's

my $string = '00110011111110111111111111111110';
   $string =~ /(1{1,}1)/; 
print $1, "\n";

prints 
       11
instead of 
       11111111111111111
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I know to search for longest string separated by 1's, I would use =~ /(1.*1)/, but here "." will pick 0's and 1's both, and I only want 1's. I tried few other combinations but didn't seem to work. any suggestions?

BharID:

Look for all matches, select the longest one, and then perform your replacement. Something like (untested):

my $string = '00110011111110111111111111111110';
my $str_to_replace;
for ($string=~/(1+)/g) {
    my $temp = $1;
    $str_to_replace = $temp if length($tmp) > length($str_to_replace);
}
if ($str_to_replace) {
    my $repl = '2' x length($str_to_replace);
    $string =~ s/$str_to_replace/$repl/;
}
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...roboticus

When your only tool is a hammer, all problems look like your thumb.

$s = '00110011111110111111111111111110';;

my $best = [0,0];;
$+[0] - $-[0] > $best->[1] and $best = [ $-[0], $+[0] - $-[0] ] 
    while $s =~ m[(1+)]g;;

substr $s, $best->[0], $best->[1], '2'x$best->[1];;

print $s;;
00110011111110222222222222222220
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---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

perl -le '$_="00110011111110111111111111111110"; $m=( sort({length($b)
+<=>length($a)} /(1+)/g ) )[0];s/$m/2 x length $m/e;print'
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And 1{1,}1 is just nonsense. It matches a minimum of two 1's, but certainly does not match the longest run of 1's in a string--it just matches the *first* run of 1's that has at least two 1's in it. For instance,

use strict;
use warnings;
use 5.010;


my $str = '110011111111';
$str =~ s/1{1,}1/*/;
say $str;

--output:--
*0011111111
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use List::Util qw(max);

use strict;
use warnings;

my $string = '00111100110';

my $longest = max map {length} $string =~ /(1+)/g;

$string =~ s/1{$longest}/'2' x $longest/eg;
print $string, "\n";
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