This solution is similar to kennethk's but uses a look-ahead in the regular expression and pos to find where the match occurred rather than special variables.

use strict;
use warnings;

use 5.010;

my @searches = qw{
   .LLL
   LLLL
   .RRR
   RRRR
   };
                
chomp( my @lines = <DATA> );

foreach my $search ( @searches )
{
    my $rxSearch = qr{(?=\Q$search\E)};
    my $length   = length $search;
    foreach my $line ( @lines )
    {
        my ( $string, $mask ) = split m{\s+}, $line, 2;
        say qq{Looking for '$search' in '$mask'};

        while ( $mask =~ m{$rxSearch}g )
        {
            my $pos = pos $mask;
            my $ind = q{ } x length $mask;
            substr $ind, $pos, $length, q{^} x $length;
            say qq{     Found at offset $pos};
            say qq{     $string\n     $mask};
            say qq{     $ind - @{ [ substr $string, $pos, $length ] }}
+;
        }
    }
}


__DATA__
THAETURQU            .LLL..RRR
JURYATAUTIOPW            .LLL...LL.RRR
TURIWOWQNQQUTYRIOPWMNHF        L..L..LLLL.LL.R..L.LLLL

[download]

The output.

Looking for '.LLL' in '.LLL..RRR'
     Found at offset 0
     THAETURQU
     .LLL..RRR
     ^^^^      - THAE
Looking for '.LLL' in '.LLL...LL.RRR'
     Found at offset 0
     JURYATAUTIOPW
     .LLL...LL.RRR
     ^^^^          - JURY
Looking for '.LLL' in 'L..L..LLLL.LL.R..L.LLLL'
     Found at offset 5
     TURIWOWQNQQUTYRIOPWMNHF
     L..L..LLLL.LL.R..L.LLLL
          ^^^^               - OWQN
     Found at offset 18
     TURIWOWQNQQUTYRIOPWMNHF
     L..L..LLLL.LL.R..L.LLLL
                       ^^^^  - WMNH
Looking for 'LLLL' in '.LLL..RRR'
Looking for 'LLLL' in '.LLL...LL.RRR'
Looking for 'LLLL' in 'L..L..LLLL.LL.R..L.LLLL'
     Found at offset 6
     TURIWOWQNQQUTYRIOPWMNHF
     L..L..LLLL.LL.R..L.LLLL
           ^^^^              - WQNQ
     Found at offset 19
     TURIWOWQNQQUTYRIOPWMNHF
     L..L..LLLL.LL.R..L.LLLL
                        ^^^^ - MNHF
Looking for '.RRR' in '.LLL..RRR'
     Found at offset 5
     THAETURQU
     .LLL..RRR
          ^^^^ - URQU
Looking for '.RRR' in '.LLL...LL.RRR'
     Found at offset 9
     JURYATAUTIOPW
     .LLL...LL.RRR
              ^^^^ - IOPW
Looking for '.RRR' in 'L..L..LLLL.LL.R..L.LLLL'
Looking for 'RRRR' in '.LLL..RRR'
Looking for 'RRRR' in '.LLL...LL.RRR'
Looking for 'RRRR' in 'L..L..LLLL.LL.R..L.LLLL'

[download]

I hope this is useful.

Cheers,

JohnGG

Update: Corrected typo.

In reply to Re: Extracting string based on comparison to second string? by johngg
in thread Extracting string based on comparison to second string? by trudy123g

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