shFlags is a library written to greatly simplify the handling of
command-line flags in Bourne based Unix shell scripts (bash, dash, ksh,
sh, zsh) on many Unix OSes (Linux, Solaris, Mac OS X, etc.).

Most shell scripts use getopt for flags processing, but the different
versions of getopt on various OSes make writing portable shell scripts
difficult.  shFlags instead provides an API that doesn't change across
shell and OS versions so the script writer can be confident that the
script will work.

(Taken from http://code.google.com/p/shflags/)