use warnings;
use strict;
use feature qw{ say };

if ("don't" =~ / (.+?) (\b{wb}) /x) {  # matches the whole string
    print "It matches\n";
    say $1;
    say $2;
}
else {
    print "It doesn't match\n";
}

if ("don't" =~ / (.+?) /x) {  # It no longer matches the whole string
    print "It matches\n";
    say $1;
}
else {
    print "It doesn't match\n";
}

Output:
It matches
don't

It matches
d