10 

    11 * Shell command.

    12 

    13 ** command.

    14 

    15 Main semantic is to invoke command instead defined function with same name:

    16 

    17   $ ls() { ls --color "$@"; }

    18   $ ls                          # infinitely loop as func invoke itself

    19   $ ls() { command ls --color "$@"; }

    20   $ ls .                        # invoke /bin/ls with color output

    21   $ unset ls                    # forget func definition

    22   $ ls                          # invoke /bin/ls without color output

    23 

    24 With '-p' arg Perform the command search using a default value for PATH that

    25 is guaranteed to find all of the standard utilities:

    26 

    27   $ command -p getconf PATH

    28 

    29 

    30 With '-v' arg work like 'which' command which not included in POSIX:

    31 

    32   $ command -v ls

    33 /usr/bin/ls

    34   $ command -v echo             # for build-in command print command itself

    35 echo                            # you can check for equality or for slash to

    36                                 # distinguish from utilities