I will spend some time to understand this part print for grep defined(), $s =~ /^$re2$/;

Maybe this will help:

#! perl -slw
use strict;

my @w = do{ local @ARGV = 'words.txt'; <> };
chomp @w;

my $s = 'couldsomeonerecommendaworkingperlmoduletosplitconcatenatedwor
+ds';

my @subset = grep{ $s =~ /$_/ } 'a', 'perl', @w;

my $re1 = join '|', sort{ length( $b ) <=> length( $a ) }@subset;
my $re2 = "($re1)?" x 20;

my @found = $s =~ /^$re2$/;

print join '|', @found;

my @undefsRemoved = grep defined(), @found;

print for @undefsRemoved;
[download]

Note: I've increase the number of repetitions from 11 to 20 to allow for sentences with more words. The side effect of that is that the unmatched captures now return undef, so If I just printed out @found, I get this:

c:\test>junk
Use of uninitialized value $found[12] in join or string at C:\test\jun
+k.pl line 15, <> line 178691.
Use of uninitialized value $found[13] in join or string at C:\test\jun
+k.pl line 15, <> line 178691.
Use of uninitialized value $found[14] in join or string at C:\test\jun
+k.pl line 15, <> line 178691.
Use of uninitialized value $found[15] in join or string at C:\test\jun
+k.pl line 15, <> line 178691.
Use of uninitialized value $found[16] in join or string at C:\test\jun
+k.pl line 15, <> line 178691.
Use of uninitialized value $found[17] in join or string at C:\test\jun
+k.pl line 15, <> line 178691.
Use of uninitialized value $found[18] in join or string at C:\test\jun
+k.pl line 15, <> line 178691.
Use of uninitialized value $found[19] in join or string at C:\test\jun
+k.pl line 15, <> line 178691.
could|someone|recommend|aw|or|king|perl|module|to|split|concatenated|w
+ords||||||||
[download]

So I use grep to remove any undefined values:

my @undefsRemoved = grep defined(), @found;
[download]

Actually it needs print "$_\n" for grep defined(), $s =~ /^$re2$/; to print line-wise.

If you look at the first line of the code I posted: #! perl -slw, the l in the -slw has the affect of adding "\n" to print statements automatically. Saves me having to type them all the time.

I can send you a link to the tool, but I am not sure it's a right way to do it through the forum.

Just post the link as text, or wrap it in brackets: [ link here ] to make it an active link.