Test for function's existence that can work on both bash and zsh?

Question

Is there a way to test whether a shell function exists that will work both for bash and zsh?

Solution 1

If you want to check that there's a currently defined (or at least potentially marked for autoloading) function by the name foo regardless of whether a builtin/executable/keyword/alias may also be available by that name, you could do:

if typeset -f foo > /dev/null; then
  echo there is a foo function
fi

Though note that if there's a keyword or alias called foo as well, it would take precedence over the function (when not quoted).

The above should work in ksh (where it comes from), zsh and bash.

Solution 2

This is pure POSIX, so it should work on all POSIX shells.

foo()
{
    echo "bar"
}

if type 'foo' 2>/dev/null | grep -q 'function'
then
   echo 'function exists'
fi

Comments

[muru]

This would also succeed if foo was an alias or an existing command instead of a function ... which may or may not matter depending on what OP intends to do with the function.

[Sagar]

well of course you can add type foo | grep "foo.*function". The bash shell will print the function definition as well. zsh shell will simply inform type is function.