use strict;
use warnings;
use re 'eval';

my $find = qr/123/;

while ( <DATA> ) {
    chomp;
    if ( m/$find(?(?{(pos()<=length($_)*.5)})|\w\b\w)/ ) {
        print "$_ matched.\n";
    } else {
        print "$_ didn't match.\n";
    }
}


__DATA__
1230000000
0123000000
0012300000
0001230000
0000123000
0000012300
0000001230
0000000123