How can I check if a program exists from a Bash script?

Question

How would I validate that a program exists, in a way that will either return an error and exit, or continue with the script?

It seems like it should be easy, but it\

Answer 1

I have a function defined in my .bashrc that makes this easier.

command_exists () {
    type "$1" &> /dev/null ;
}

Here's an example of how it's used (from my .bash_profile.)

if command_exists mvim ; then
    export VISUAL="mvim --nofork"
fi