Anchor(faq83)

How do I determine whether a function is already defined?

There are several answers, all of which require Bash (or at least, non-Bourne) commands:

# These two are best:
if [[ $(declare -f foo) ]]     # it prints nothing, if undefined
if declare -f foo >/dev/null   # it also sets the exit status

# These are a little more obvious, but...
if [[ $(type foo 2>&1) = *\ is\ a\ function* ]]
if type foo >/dev/null 2>&1 && ! type -f foo >/dev/null 2>&1

A related question is, Why on earth does anyone want this? Why not just define the function already?

I don't know. I think it has something to do with [http://en.wikipedia.org/wiki/Reflection_%28computer_science%29 reflection]. But people keep asking it, so....