What is the best method to test if a program exists for a shell script?

Question

I'm just curious to know how to best check if a program exists. I've seen solutions with

• test
• command
• hash
• type
• which
• [

Which is the best method, is there a right answer? What does the POSIX and LSB specs say about this?

Answer 1

You probably want to use the command command, e.g.:

command -v <the_command>

For more discussion see the following StackOverflow posts:

• Find out if a command exists on POSIX system

• Check if a program exists from a Bash script

Also see the following Unix StackExchange post:

• How do I test to see if an application exists in $PATH?