How can I check if a command exists in a shell script?

Shell Problem Overview

I am writing my first shell script. In my script I would like to check if a certain command exists, and if not, install the executable. How would I check if this command exists?

if # Check that foobar command doesnt exist
then
    # Now install foobar
fi

Shell Solutions

Solution 1 - Shell

In general, that depends on your shell, but if you use bash, zsh, ksh or sh (as provided by dash), the following should work:

if ! type "$foobar_command_name" > /dev/null; then
  # install foobar here
fi

For a real installation script, you'd probably want to be sure that type doesn't return successfully in the case when there is an alias foobar. In bash you could do something like this:

if ! foobar_loc="$(type -p "$foobar_command_name")" || [[ -z $foobar_loc ]]; then
  # install foobar here
fi

Solution 2 - Shell

Five ways, 4 for bash and 1 addition for zsh:

type foobar &> /dev/null
hash foobar &> /dev/null
command -v foobar &> /dev/null
which foobar &> /dev/null
(( $+commands[foobar] )) (zsh only)

You can put any of them to your if clause. According to my tests (https://www.topbug.net/blog/2016/10/11/speed-test-check-the-existence-of-a-command-in-bash-and-zsh/), the 1st and 3rd method are recommended in bash and the 5th method is recommended in zsh in terms of speed.

Solution 3 - Shell

Try using type:

type foobar

For example:

$ type ls
ls is aliased to `ls --color=auto'

$ type foobar
-bash: type: foobar: not found

This is preferable to which for a few reasons:

The default which implementations only support the -a option that shows all options, so you have to find an alternative version to support aliases
type will tell you exactly what you are looking at (be it a Bash function or an alias or a proper binary).
type doesn't require a subprocess
type cannot be masked by a binary (for example, on a Linux box, if you create a program called which which appears in path before the real which, things hit the fan. type, on the other hand, is a shell built-in (yes, a subordinate inadvertently did this once).

Solution 4 - Shell

The question doesn't specify a shell, so for those using **fish** (friendly interactive shell):

if command -v foo > /dev/null
  echo exists
else
  echo does not exist
end

For basic POSIX compatibility, we use the -v flag which is an alias for --search or -s.

Solution 5 - Shell

https://stackoverflow.com/questions/592620/check-if-a-program-exists-from-a-bash-script covers this very well. In any shell script, you're best off running command -v $command_name for testing if $command_name can be run. In bash you can use hash $command_name, which also hashes the result of any path lookup, or type -P $binary_name if you only want to see binaries (not functions etc.)

Solution 6 - Shell

A function which works in both bash and zsh:

# Return the first pathname in $PATH for name in $1
function cmd_path () {
  if [[ $ZSH_VERSION ]]; then
    whence -cp "$1" 2> /dev/null
  else  # bash
     type -P "$1"  # No output if not in $PATH
  fi
}

Non-zero is returned if the command is not found in $PATH.

Solution 7 - Shell

A function I have in an install script made for exactly this

function assertInstalled() {
    for var in "$@"; do
        if ! which $var &> /dev/null; then
            echo "Install $var!"
            exit 1
        fi
    done
}

example call:

assertInstalled zsh vim wget python pip git cmake fc-cache

Solution 8 - Shell

which <cmd>

also see options which supports for aliases if applicable to your case.

Example

$ which foobar
which: no foobar in (/usr/local/bin:/usr/bin:/cygdrive/c/Program Files (x86)/PC Connectivity Solution:/cygdrive/c/Windows/system32/System32/WindowsPowerShell/v1.0:/cygdrive/d/Program Files (x86)/Graphviz 2.28/bin:/cygdrive/d/Program Files (x86)/GNU/GnuPG
$ if [ $? -eq 0 ]; then echo "foobar is found in PATH"; else echo "foobar is NOT found in PATH, of course it does not mean it is not installed."; fi
foobar is NOT found in PATH, of course it does not mean it is not installed.
$

PS: Note that not everything that's installed may be in PATH. Usually to check whether something is "installed" or not one would use installation related commands relevant to the OS. E.g. rpm -qa | grep -i "foobar" for RHEL.

Content Type	Original Author	Original Content on Stackoverflow
Question	Andrew	View Question on Stackoverflow
Solution 1 - Shell	Ivan Tarasov	View Answer on Stackoverflow
Solution 2 - Shell	xuhdev	View Answer on Stackoverflow
Solution 3 - Shell	Foo Bah	View Answer on Stackoverflow
Solution 4 - Shell	Dennis	View Answer on Stackoverflow
Solution 5 - Shell	Morten	View Answer on Stackoverflow
Solution 6 - Shell	Tom Hale	View Answer on Stackoverflow
Solution 7 - Shell	mgild	View Answer on Stackoverflow
Solution 8 - Shell	Kashyap	View Answer on Stackoverflow