Grep default color option

Simply add the following alias to your shell's configuration file, e.g. .bashrc or .bash_profile (depending on which you use, see here):

alias grep='grep --color=auto'

You can simply use it as grep.

There's usually no need to make scripts when simple command aliases do the same thing just fine. In fact your script wouldn't even work if you wanted to pass more options to grep. In case you need a tiny snippet that can deal with arguments, you should use functions.

#!/bin/sh
exec grep --color "$@"

This illustrates the standard way of "wrapping" a command with a shell script, when the command doesn't quite work the way that you like.

The exec avoids creating an extra process (one for the script and one for grep). You could leave it out if you like.

The "$@" is replaced by all of the script's arguments, no matter how many there are. It correctly preserves arguments with spaces and other characters that are special to the shell.