"Martin Schwenke" <mar...@meltin.net> wrote: > Neither bash.info or bash(1) documents parameter expansion of the > form: > > ${parameter+word}
It's documented, but it's easy to miss. Just before the list of parameter expansion forms is this paragraph: In each of the cases below, word is subject to tilde expansion, parameter expansion, command substitution, and arithmetic expansion. When not performing substring expansion, bash tests for a parameter that is unset or null; omitting the colon results in a test only for a parameter that is unset. paul