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

If using other languages, how about python:

cmnstr() { python -c "from difflib import SequenceMatcher
s1, s2 = ('''$1''', '''$2''')
m = SequenceMatcher(None,s1,s2).find_longest_match(0,len(s1),0,len(s2))
if m.a == 0: print(s1[m.a: m.a+m.size])"
}
$ cmnstr x y
$ cmnstr asdfas asd
asd

(h/t to @RickardSjogren's answer to stack overflow 18715688)