Longest common prefix of two strings in bash

Question

I have two strings. For the sake of the example they are set like this:

string1=\"test toast\"
string2=\"test test\"

What I want is to find

Answer 1

It's probably simpler in another language. Here's my solution:

common_bit=$(perl -le '($s,$t)=@ARGV;for(split//,$s){last unless $t=~/^\Q$z$_/;$z.=$_}print $z' "$string1" "$string2")

If this weren't a one-liner, I'd use longer variable names, more whitespace, more braces, etc. I'm also sure there's a faster way, even in perl, but, again, it's a trade-off between speed and space: this uses less space on what is already a long one-liner.