Making a program with any input in stdin, and which breaks when 42(aka. The Famous Life, the Universe, and Everything Solution) is entered.
In example:
$ cat ./nums.lst
3249
32
434
233
323
42
405
84
$ cat ./nums.lst | ./42.out
3249
32
434
233
323
The solution might be in one of these languages: ADA, ASM, BASH, BF, C, C99 strict, CAML, CLOJ, CLPS, COB, CPP 4.3.2, CPP 6.3, CPP14, CS2, D, ERL, FORT, FS, GO, HASK, ICK, ICON, JAVA, JS, kotlin, LISP clisp, LISP sbcl, LUA, NEM, NICE, NODEJS, PAS fpc, PAS gpc, PERL, PERL6, PHP, PIKE, PRLG, PYPY, PYTH, PYTH 3.5, RUBY, rust, SCALA, SCM chicken, SCM guile, SCM qobi, ST, swift, TCL, TEXT, WSPC.
And the whole source code is limited to 50000 Bytes.
From an original challenge found at https://www.codechef.com/problems/TEST.