Rails' alias_method_chain for Bash

Rails has a great trick for monkey-patching in decorators, called aliasmethodchain. While long-term use is perhaps discouraged, it's awesome if you need to just insert some behavior in a hurry.

Using bash's introspection support, we can achieve the same thing for shell functions:

function decorate {
  local base=$1
  local feature=$2
  local undecorated="${base}_without_${feature}"
  local decorated="${base}_with_${feature}"

  # Define $undecorated with $base's body
  eval "$(echo 'function' $undecorated; declare -f $base | tail -n +2)"

  # Define $base with $decorated's body
  eval "$(echo 'function' $base; declare -f $decorated | tail -n +2)"
}

Here's how to use it:

$ function theirfunc { echo do their thing; }
$ function theirfunc_with_mything {
> echo do my thing
> theirfunc_without_mything
> }
$ decorate theirfunc mything
$ theirfunc
do my thing
do their thing

Reposted from SO: http://stackoverflow.com/a/4727925/580412