Check if a program exists from your bash script

Lately I’ve had the bash bug… and I’m continually impressed at what can be accomplished with this tool. Just the other day, I needed to check for the existence of some programs before doing the rest of my scripting work. Originally I was doing this with which, but after reading this detailed stackoverflow answer, I’m now using the more portable command -v. A sample script and examples follow.

Script

#!/bin/bash

programs="${@}"

print_usage() {
  printf "Usage:\\n"
  printf "  ${0} <programs>\\n"
  printf "Examples:\\n"
  printf "  ${0} cp\\n"
  printf "  ${0} cp mv cat\\n"
}

check_for_program() {
  local program 
  program="${1}"

  printf "Checking for ${program}\\n  "
  command -v "${program}"

  if [[ "${?}" -ne 0 ]]; then
    printf "${program} is not installed, exiting\\n"
    exit 1
  fi 
}

main() {
  if [[ -z "${programs}" ]]; then 
    print_usage 
    exit 1
  fi 

  for p in ${programs}; do 
    check_for_program "${p}"
  done
}

main 

Examples

$ ./check_for_program.bash
Usage:
  ./check_for_program.bash <programs>
Examples:
  ./check_for_program.bash cp
  ./check_for_program.bash cp mv cat

$ ./check_for_program.bash cp mv cat
Checking for cp
  /bin/cp
Checking for mv
  /bin/mv
Checking for cat
  /bin/cat

$ ./check_for_program.bash foobar
Checking for foobar
  foobar is not installed, exiting