Linux which command options

Which Command in Linux [Explained with Examples]

Linux which command is an extremely useful command for locating executable files located anywhere in the Linux system. Learn how to use it.

If you are wondering where exactly is a certain program is located, simply use which on it. The which command locates an executable file in your shell’s search path.

This Linux command has a simple syntax:

Let’s see how to use this simple but useful command.

Linux which command examples

Let’s say you want to know where is the Java executable, use which command:

The output could be like this:

Note that which only works on executable files. So you should use it only with the argument that you can run. For example, you install Java through the JDK package but you don’t run a command called ‘jdk’, you run ‘java’. So you use which command on java, not jdk.

If the which command doesn’t find the executable in the current path, it returns nothing.

Using which command with multiple executable files

You can provide more than one argument to which command:

which man java python nada

[email protected]:~$ which man java python nada /usr/bin/man /usr/bin/java /usr/bin/python

Did you notice something here? I gave it four arguments but the result is displayed for three of them only. It’s because ‘nada’ is not an executable. There is no output for that.

Display all pathnames with which command

The which command in Linux has only one option, -a. By default, which command prints only one pathname for its arguments.

If a program has executable in two places, say in /usr/bin/program and in /usr/local/bin/program, you can display both pathnames using the -a option.

Exit status of which command

If you use which command in a bash script, you may need to know its exit status.

Which command has the following exit status:

• 0 – all arguments are found and executable
• 1 – one or more arguments is nonexistent or non-executable
• 2 – if an invalid option is specified

That’s all you need to know about which command in Linux. If you have questions or suggestions, do let me know in the comments below.

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How to Use the which Command in Linux, With Examples

This tutorial will teach you how to use the which command in Linux with some simple examples.

The which command will tell you the path to the executable used by a command on the system if it exists.

Why is this useful? Say you’ve got two copies of the MySQL executable installed on your system (installed via different means), and you want to know which one is actually in use so that the other can be removed – the which command can tell you which of the two is called when you execute MySQL on the command line.

Linux which Command Syntax

The command for the which command is as follows:

• OPTIONS is an optional list of options from the below table which can be used to change the default behavior of the which command
• COMMAND is the name of the command you wish to know the path to the executable for
  • The COMMAND must be supplied, or which will have nothing to look for!

  Command Options

  Here are the most commonly used options which can be passed to the which command:

  –all, -a	Print all matching executables in PATH, not just the first.
  –read-alias, -i	Read aliases from stdin, reporting matching ones on stdout. This is useful in combination with using an alias for which itself.
  –skip-alias	Ignore option –read-alias’, if any. This is useful to explicitly search for normal binaries, while using the –read-alias’ option in an alias or function for which.
  –read-functions	Read shell function definitions from stdin, reporting matching ones on stdout. This is useful in combination with using a shell function for which itself.
  –skip-functions	Ignore option –read-functions’, if any. This is useful to explicitly search for normal binaries, while using the –read-functions’ option in an alias or function for which.

  As always, you can view the full user manual for the which command by running:

  which Command Examples

  Below, we look for the path for the executable, which is called when nano is run from the terminal:

  This will return something like the following if the nano text editor is installed on your system:

  If nano is not installed, you’ll see:

  This makes the which command useful for both checking where an executable is located and whether a package is installed/available or not.

  Multiple executable names can be supplied if you wish to look up multiple commands at once:

  Return Codes

  If you are using which in a Shell Script, you can use the status code returned by the command to determine whether an executable path was found or not:

  0	All specified commands were found and are executable.
  1	One or more of the specified commands was not found or is not executable.
  2	Invalid options or syntax were used.

  This can be super useful if you want to make your shell scripts more portable – you can use the which command to check that a command is available before executing it in your script, to make sure the end-user doesn’t receive any errors if they do not have the required software installed.

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  Linux which command options

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  How to Use the which Command in Linux

  The which command allows users to search the list of paths in the $PATH environment variable and outputs the full path of the command specified as an argument. The command works by locating the executable file matching the given command.

  In this tutorial, you will learn to use the which command.

  

  Linux which Command Syntax and Options

  The syntax for the which command is:

  The [argument] variable specifies the command or commands you want to find.

  For example, the following command outputs the location of the cat command:

  

  The which command has only one option, -a . It is optional and used to print all the matches it finds.

  The command searches for matches from left to right. If there are multiple matches found in the directories listed in $PATH , which prints only the first one. The -a option instructs which to print all the matches.

  Important: On many Linux distributions, which excludes the shell built-in commands and does not output their location.

  

  Having multiple matches sometimes means one match is a symlink to the other. However, it is possible to have two versions of the same command in different locations or two different commands using the same name.

  Note: Unlike many other commands, which has no —help option. To see the command description and help, run man which .

  Exit Status

  The which command returns one of the following values that indicate its exit status:

  • 0 . All arguments were found and executable.
  • 1 . One or more arguments don’t exist or aren’t executable.
  • 2 . An invalid option has been specified.

  Linux which Command Examples

  The following examples showcase how the which command works and how to use the available option.

  1. Display the Path of Any Executable File

  To display the path of any command, pass the command name as an argument after which .

  

  The output shows the path to the tr command executable file, located in /usr/bin/tr.

  2. Display Multiple Paths of Executable Files

  which accepts multiple arguments and outputs the path to each one in the specified order.

  

  The command works through the supplied list and outputs the results for the nc command, mount command, and sort command, separating each result with a newline character.

  3. List All Instances

  which only shows the first match it finds in the $PATH variable directory list. Use the -a option to show every match for the specified command.

  For example, searching for instances of the less command outputs two results when using the -a option:

  

  Use the ls command to check file details and determine if both versions are executable files. Run:

  ls -lh /usr/bin/less ls -lh /bin/less

  

  The output shows two identical versions of the same command in two locations, both 176 KB large, and both executable.

  Note: The /bin directory contains executables that can be used by the system administrator and any other user, and which are required for emergency system repairs. The /usr/bin directory is the primary directory for executable commands on the system.

  4. Find Symbolic Links

  Using the -a option lists all the paths containing an instance of the specified program. While multiple versions of the same program can exist on a system, sometimes one of the instances is only a symbolic link and not a binary file.

  For example, running the following command outputs two instances of the atq command:

  

  Again, use the ls command to check the details for both files. Run:

  ls -lh /usr/bin/atq ls -lh /bin/atq

  

  The output shows that both files are symbolic links ( -> ) only 2 bytes large and pointing to the at command.

  5. Exclude Shell Built-ins

  As previously mentioned, the which command excludes shell built-ins from its output.

  For example, asking for the location of the read and man commands only outputs the location for the man command executable file, as read is a bash shell command.

  

  This tutorial showed how to use the which command in Linux to find the path to a command’s executable binary. See and download our Linux commands cheat sheet for other essential Linux commands and examples of using them.

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  Linux which command

  

  On Unix-like operating systems, the which command locates the executable file associated with a given command.

  This page covers the Linux version of which.

  Description

  which returns the pathnames of the files (or links) which would be executed in the current environment, had the filename (or filenames) been given as a command (or commands) in a strictly POSIX-conformant shell. It does this by searching the paths in the PATH environment variable for executable files matching the names of the arguments.

  which does not follow symbolic links.

  Syntax

  Options

  Exit status

  which returns the following value, depending on what occurred:

  0	All filenames were found, and all were executable.
  1	One or more filenames were not found, or were not executable.
  2	An invalid option was specified.

  Examples

  Locates the pathname of the file which would run if the sh command were executed. On most systems, this will output:

  Related commands

  find — Find files within a directory hierarchy.
  whereis — Locate the binary, source, and manual page files for a command.

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