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 had to check if Git was installed as part of deploying our CI server. My final Bash script was as follows (Ubuntu server):

if ! builtin type -p git &>/dev/null; then
  sudo apt-get -y install git-core
fi