Create multi-word alias in bash?

Question

I want to create an alias in bash, such that

git diff somefile

becomes

git diff --color somefile

But I don't want to define my own custom alias like

alias gitd = "git diff --color"

because if I get used to these custom alias, then I loose the ability to work on machines which don't have these mappings.

Edit: It seems bash doesn't allow multi-word alias. Is there any other alternative solution to this apart from creating the alias?

Answer 1

To create a smarter alias for a command, you have to write a wrapper function which has the same name as that command, and which analyzes the arguments, transforms them, and then calls the real command with the transformed arguments.

For instance your git function can recognize that diff is being invoked, and insert the --color argument there.

Code:

# in your ~/.bash_profile

git()
{
  if [ $# -gt 0 ] && [ "$1" == "diff" ] ; then
     shift
     command git diff --color "$@"
  else
     command git "$@"
  fi
}

If you want to support any options before diff and still have it add --color, you have to make this parsing smarter, obviously.