use strict;
use warnings;

my $match1 = 'something ';
my $fill = 'xxxxxx ';
my $match2 = 'somethingelse ';
my $nomatch = 'nomatch ';
my @targets = (
    "$nomatch$fill$match1$match2$nomatch",
    "$nomatch$fill$match1$fill$match2$nomatch",
    "$nomatch$fill$match1$fill$nomatch$fill$match2$nomatch",
    );
    
for my $test (@targets) {
    if ($test =~ /$match1 ((?:(?!$nomatch) .)*) $match2/x) {
        print "Matched >$1< for: $test\n";
    } else {
        print "Failure for $test\n";
    }
}