which

Locate a program file in the user’s path.

For each of its arguments which prints to stdout the full path of the executable(s). It does this by searching the directories listed in the environment variable PATH.

Syntax
      which [options] [--] program_name [...]

Options
    --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.
        For example  alias which='alias | which -i'.

    --skip-alias
        Ignore option --read-alias, if any.  This is useful to explicity search
        for normal binaries, while using the --read-alias option in an alias for which.

    --skip-dot
        Skip directories in PATH that start with a dot.

    --skip-tilde
        Skip directories in PATH that start with a tilde and
        executables which reside in the HOME directory.

    --show-dot
        If a directory in PATH starts with a dot and a matching 
        executable was found for that path, then print
        "./program_name" rather than the full path.

    --show-tilde
        Output a tilde when a directory matches the HOME directory.
        This option is ignored when which is invoked as root.

    --tty-only
        Stop processing options on the right if not on tty.

    --version, -v, -V
        Print version information on standard output then exit successfully.

    --help
        Print usage information on standard output then exit successfully.

RETURN VALUE
       Which returns the number of failed arguments, or -1 when
       no programname was given.

EXAMPLE
       A useful way to use this utility is by adding an alias for
       which like the following:

       alias which='which --tty-only --show-tilde --show-dot'

       This will print the readable ~/ and ./ when starting which
       from  your prompt, while still printing the full path when
       used from a script:

              > which q2
              ~/bin/q2
              > echo 'which q2'
              /home/carlo/bin/q2

       Aliases are also supported, through the use  of  an  alias
       for  which  itself.   An  example  alias for which that is
       using this feature is as follows:

       alias which='alias | which --tty-only --read-alias --show-tilde --show-dot'

       This will print the output of alias for  each  alias  that
       matches  one  of  the given arguments.  For example, using
       this alias on itself in a tcsh:

              $ alias which alias \| /usr/bin/which -i !\*
              $ which which
              which   (alias | ./which -i !*)
                      /usr/bin/which

BUGS
       The HOME directory is determined by looking for the HOME environment variable,
       which exits when this variable doesn’t exist.
       Which will consider two equivalent  directories to be different when one of
       them contains a path with a symbolic link.

Some shells may provide a builtin which command which is similar or identical to this utility.

“A man should never be ashamed to own he has been in the wrong, which is saying in other words, that he is wiser today than he was yesterday” ~ Alexander Pope (thoughts on various subjects)

Related Linux commands

pwd - Print Working Directory.
hash - Remember the full pathname of a name argument.
pathchk - Check file name portability.
whereis - Search the user’s $path, man pages and source files for a program.
Equivalent Windows commands: WHERE - Locate files /(get-command $file).Definition