Cant think of an elegant lua solution to this little problem

Hi

I am trying to sort a big list of arbitrary keyname strings in a table. I am using the standard table sort with a custom sort function. The little snag I hit was with strings like this

ABC_1
ABC_2
ABC_19
ABC_20

I want to do a lexical sort on my strings but for strings like those above, sort in that order, but of course I get

ABC_1
ABC_19
ABC_2
ABC_20

I cant think of a concise Lua way of doing a lexical sort of strings but still manage to get these numeric type examples correct too. Any suggestions please ?

Regards Geoff