use strict;
use warnings;

while ( my $string = <DATA> ) {
    chomp $string;
    if ( $string =~ m/(\w+)\s((??{"[$1]+"}))/ ) {
        print "$string => matched: $1, $2!\n";
    } else {
        print "$string => Didn't match.\n";
    }
}


__DATA__
abcde fgh
abcde eadcabe