There seems to be a bug in expr (both 1.1.3 and svn): # ./busybox expr xyz0 : '[^0-9]\+\([0-9]\+\)' returns 0 on stdout and an error code 1. # ./busybox expr xyz1 : '[^0-9]\+\([0-9]\+\)' returns 1 on stdout and an error code 0. Cheers, Cristian