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

Question

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

User · Answer

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.

User · Answer

Five ways  4 for bash and 1 addition for zsh    type foobar  amp  gt   dev null hash foobar  amp  gt   dev null command -v foobar  amp  gt   dev null which foobar  amp  gt   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

User · Answer

which  lt cmd gt   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

User · Answer

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

User · Answer

The question doesn t specify a shell  so for those using fish  friendly interactive shell    if command -v foo  gt   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

User · Answer

A function I have in an install script made for exactly this  function assertInstalled         for var in       do         if   which  var  amp  gt   dev null  then             echo  Install  var               exit 1         fi     done     example call   assertInstalled zsh vim wget python pip git cmake fc-cache

User · Answer

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

User · Answer

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   gt   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

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

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