isaacs/npm — comment on commit d753758a8d1d1525b8cb879c8de4674abb8d6975
File:  line 0
By clvv:

It's actually a POSIX feature, http://pubs.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_06_02. I tested it on zsh, bash, pdksh, mksh, dash, busybox ash hush, FreeBSD's /bin/sh. OpenBSD's /bin/sh. I don't know which sh you're refering to, but I can't get hold of those old UNIX sh, so I could not test on all variants. I don't know how many people install npm on old UNIXs. Nonetheless, I think it should work here.