Forth was sort of designed by and for people who did want to solve these essential problems anew for each application. Chuck Moore claimed many times that a tailored ("ad hoc") solution that solves only the part of the problem you need to solve for a particular application would be 10× smaller and simpler than a generalized solution that has to balance the needs of all possible applications. He considered it preferable to not have a lot of library code in your application to solve problems you don't actually have. Maybe your ad-hoc solution is brittle, but it's brittle precisely in ways you know about, not in ways you don't.

But you don't have to use Forth that way just because Chuck did. You can totally use a generalized string library in Forth. I don't know which one to recommend, but http://turboforth.net/resources/string_library.html seems to be one possibility.

You can be sure that Python's file.readlines()† will have trouble if you try to read a line that is much longer than your RAM size.

You can get pretty far with just built-in standard functionality, though:

    Gforth 0.7.3, Copyright (C) 1995-2008 Free Software Foundation, Inc.
    Gforth comes with ABSOLUTELY NO WARRANTY; for details type `license'
    Type `bye' to exit
    128 constant len  create buf len allot  ok
    : greet ." Name? "  buf len accept  ." Hello, " buf swap type ." !" ;  ok
    greet Name? Zelphir Hello, Zelphir! ok

    include string.fs

† ever since Python 2.0, I'd recommend using list(file) instead of file.readlines(), or just iterate over the file directly, like [line.strip() for line in file if line.startswith('zel')]