What is the 'function' keyword used in some bash scripts?

Question

For example: Bash-Prog-Intro-HOWTO

function foo() {}

I make search queries in info bash and look in releted chapters of POSIX for

Answer 1

The function keyword is necessary in rare cases when the function name is also an alias. Without it, Bash expands the alias before parsing the function definition -- probably not what you want:

alias mycd=cd
mycd() { cd; ls; }  # Alias expansion turns this into cd() { cd; ls; }
mycd                # Fails. bash: mycd: command not found
cd                  # Uh oh, infinite recursion.

With the function keyword, things work as intended:

alias mycd=cd
function mycd() { cd; ls; }  # Defines a function named mycd, as expected.
cd                           # OK, goes to $HOME.
mycd                         # OK, goes to $HOME.
\mycd                        # OK, goes to $HOME, lists directory contents.