sub trunc_match
{
        my ($what) = @_;
        my @bits;

        for (1..length $what)
        {
                push (@bits,$what);
                chop $what;
        }

        return '('.join ('|', map { quotemeta($_) } @bits).')$';
}

my $rx = trunc_match ("foobar");

$_ = "This sentence ends in foob";

if (/$rx/)
{
        print "Truncated, ends in '$1'\n";
}

##</code><code>##

(foobar|fooba|foob|foo|fo|f)$