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12 Linux Which Command, Whatis Command, Whereis Command Examples

This Linux tutorial will explain the three “W” commands. The three “W”s are whatis, whereis and which commands.

You already know how to use find command to efficiently fo find a file.

Now, these three W commands will help you to locate more stuff from Linux command line.

I. Linux whatis Command

Whatis command is helpful to get brief information about Linux commands or functions. Whatis command displays man page single line description for command that matches string passed as a command line argument to whatis command. Whatis command searches for string in its index databases which is maintained by mandb program. Whatis command picks short description of NAME section of man page of command that matches to input given to the whatis command.

Whatis provides several command line options to help user in getting brief information of specific Linux commands as per their need or interest.

Syntax:

$ whatis [-options]

For example, here is the output of whatis command, when it is run without any option.

$ whatis write
write (1)            - send a message to another user
write (2)            - write to a file descriptor

It displays brief information about “write” from man pages.

1. Get information from specific sections of man pages using -s option

If we want to get Linux command information from specific section of man pages, then we can provide sections list using “-s or —sections or –section” option. It will restrict whatis command to display brief information from specified man page section only.

$ whatis -s "1","2" open
open (1)             - start a program on a new virtual terminal (VT).
open (2)             - open and possibly create a file or device

It displays open command and function brief information from man page sections 1 and 2.

$ whatis -s "2" open
open (2)             - open and possibly create a file or device

It displays open function brief information from man page section 2.

2. Search information through wild-cards using -w option

If we want to search Linux commands or functions information using wild card, then whatis command gives “-w or –wildcard” option. It will make your search specific as per user’s need.

$ whatis -w 'ab*'
abort (3)            - cause abnormal process termination
abs (3)              - compute the absolute value of an integer

It displays brief information of Linux commands or functions which start from “ab”.

$ whatis -w 'ab?'
abs (3)              - compute the absolute value of an integer

It displays brief information of Linux commands or functions which start from “ab” and followed by any single character.

3. Search information through regular expressions using -r option

If we want to search Linux commands or functions information using regular expressions, then whatis command gives “-r or –regex” option. It will give flexibility to customize your search for Linux commands or functions throughout the Linux system.

$ whatis -r '^ab'
abort (3)            - cause abnormal process termination
abs (3)              - compute the absolute value of an integer

It displays brief information of Linux commands or functions which start from “ab”.

$ whatis -r 'ab$'
anacrontab (5)       - configuration file for anacron
baobab (1)           - A graphical tool to analyse disk usage
crontab (1)          - maintain crontab files for individual users (Vixie Cron)
crontab (5)          - tables for driving cron
fstab (5)            - static information about the filesystems
inittab (5)          - init daemon configuration
swab (3)             - swap adjacent bytes
tc-stab (8)          - Generic size table manipulations

It displays brief information of Linux commands or functions which ends with “ab”.

4. Disable trimmed output using -l option

Generally whatis command trims long output of Linux commands or functions information to avoid “Not good” output display on terminal that is going beyond screen. To allow whatis command to show complete output on screen, “-l or –long” option can be used.

$ whatis ssh-import-id
ssh-import-id (1)    - retrieve one or more public keys from a public keyserver (Launchpad.net by default) and append them to the current user's authorized_keys file (or some other specifie...

It displays trimmed output of brief information of Linux command.

$ whatis -l ssh-import-id
ssh-import-id (1)    - retrieve one or more public keys from a public keyserver (Launchpad.net by default) and append them to the current user's authorized_keys file (or some other specified file)

It displays complete output of brief information of Linux command.

5. Restrict search up to specified path using -M option

By default, whatis command uses $MANPATH environment variable. But whatis provides “-M or –manpath” option to restrict search up to specified path of man pages.

$ whatis -M /usr/share/man hexdump
hexdump (1)          - ASCII, decimal, hexadecimal, octal dump

It displays brief information of Linux hexdump command from man pages available at path /usr/share/man.

$ whatis -M /usr/man hexdump
hexdump: nothing appropriate.

It could not find brief information of Linux hexdump command from specified path /usr/man.

II. Linux whereis Command

Whereis command is helpful to locate binary, source and manual pages of commands in the Linux system. It is very simple utility and provides several options which are given below with examples.

Syntax:

$ whereis [-options]

For example, whereis command is run without any option.

$ whereis open
open: /bin/open /usr/share/man/man1/open.1.gz /usr/share/man/man2/open.2.gz

It locates binary, source and man pages of “open” command and here it displayed paths where binary, man pages of open command is available in the system.

6. Locate binaries using -b option

If we want to locate binary of Linux command, use “-b” option.

$ whereis -b whereis
whereis: /usr/bin/whereis /usr/bin/X11/whereis

It locates binary of “whereis” command and displays paths where binary of command is available in the system.

7. Locate man pages for a command using -m option

If we want to locate man page of Linux command, use “-m” option.

$ whereis -m whereis
whereis: /usr/share/man/man1/whereis.1.gz

It locates man page of “whereis” command and displays path where man page of command is available in the system.

8. Locate source of a command using -s option

If we want to locate source of Linux command, use “-s” option.

$ whereis -s whereis
whereis:

It locates source of “whereis” command, but source of “whereis” command does not exist in the system, so it did not display path for source of command in the system.

9. Locate unusual entries using -u option

This option is something different that searches for unusual entries. These entries are those command whose source, binary or man page does not exist in the system as per options “[-bms]” specified along with “–u”.

$ whereis  -m  -u wcgrep
wcgrep:

It checks if specified command (i.e. wcgrep) man page does not exist in the system. Whereis command with options “-m and -u” locates for the commands in the system whose man page does not exist.

$ whereis  -m  -u grep
$

Here, whereis command with same options is applied on “grep” command whose man page exists in the system, so whereis returned nothing and exits normally.

10. Locate binaries in a specified path using -B option

If user wants to search for binary and wants to limit the scope of search for whereis command up to specified path, then use “-B” option.

$ whereis -B /bin -f for_loop
for_loop: /bin/for_loop

It locates binary of “for_loop” user program from path “/bin”.

$ whereis -B /usr -f open
open: /usr/share/man/man1/open.1.gz /usr/share/man/man2/open.2.gz

If open command’s binary is not found at specified path, then it is not shown but whereis command by default searches for other types (i.e. man page and source) of specified command (i.e. open) and displays them if found.

11. Locate man pages with limited scope using -M option

If user wants to search for man pages and wants to limit the scope of search for whereis command up to specified path, then use “-M” option.

$ whereis -M /usr/share/man/man1 -f open
open: /bin/open /usr/share/man/man1/open.1.gz
$ whereis -M /usr/share/man/man2 -f open
open: /bin/open /usr/share/man/man2/open.2.gz
$ whereis -M /usr/share/man/man3 -f open
open: /bin/open

Here, it is observed that whereis command is displaying man page of “open” command which is available in specified path only. But, whereis command by default searches for other types (i.e. binary and source) of specified command (i.e. open) and displays them if found.

III. Linux which Command

Which command is very small and simple command to locate executables in the system. It allows user to pass several command names as arguments to get their paths in the system. “which” commands searches the path of executable in system paths set in $PATH environment variable.

Syntax:

$ which [-option]

For example,

$ which ls gdb open grep
/bin/ls
/usr/bin/gdb
/bin/open
/bin/grep

It locates command names – “ls”, “gdb”, “open” and “grep” specified as arguments to “which” command and displays paths of each executable where it exists in the system.

12. Display all the paths using -a option

“which” command gives option “-a” that displays all paths of executable matching to argument.

$ which echo
/usr/sbin/echo

Above will search display the executable “echo” from all paths set in $PATH environment variable and displays the first path where echo executable is found. It may be case that executable is placed at other paths of $PATH environment variable as well. To get all paths where executable is present in the system, “-a” option can be used.

$ which -a  echo
/usr/sbin/echo
/bin/echo

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{ 17 comments… add one }

  • Jalal Hajigholamali April 23, 2013, 9:56 am

    Hi,

    Thanks a lot,
    Simple, beautiful and very useful commands for admin
    Thanks again

  • Anthony April 23, 2013, 10:15 am

    very useful,I enjoy all the insights you send, i learn a lot from these e-mail. Thanks.

  • Júlio Hoffimann Mendes April 23, 2013, 3:05 pm

    Another alternative is the `apropos’ tool.

    Nice post,
    Júlio.

  • Ehan Chang April 23, 2013, 4:26 pm

    very helpfull, thanks.

  • Donald Ellis April 23, 2013, 5:40 pm

    Nice treatment, however I found some problems with whereis (which looks really useful and has some really fine options).

    On Mac OSX 10.8.3, the man page has this comment:

    The historic flags and arguments for the whereis utility are no longer available in this version.

    It shows a date of 1995, indicating that the flags you mentioned may have been dropped around that time or before (or maybe other flags were present before then and the ones you show added much later).

    A query of Homebrew indicated no alternative formulas from that source. Any suggestions how to install a fully functional version of whereis on a current (since 1995) Mac system?

    A check of Ubuntu 10.04 indicate a similar version to what you have, however an OpenBSD 4.8 installation indicates only the -1 flag is available.

  • Donald Ellis April 23, 2013, 5:43 pm

    I have long loved the which command, especially the -a option, which is very frustrating when I find a system that doesn’t have -a. To remedy this, I found this replacement for which, to install in your ~/bin or wherever else you have write (and execute) access:

    : /bin/sh
    # which – which command in $PATH would be executed (from K&P)

    opath=$PATH
    PATH=/bin:/usr/bin

    all=no
    case $# in
    0)
    echo ‘usage: which [-a] command’ 1>&2
    exit 2
    ;;
    1)
    ;;
    *)
    case $1 in
    -a)
    all=yes
    shift
    ;;
    esac
    ;;
    esac

    code=1
    for i in `echo $opath | sed ‘s/^:/.:/
    s/::/:.:/g
    s/:$/:./
    s/:/ /g’`
    do
    if [ -x $i/$1 ]
    then
    echo $i/$1
    case $all in
    yes)
    code=0 ;; # found one – try for more
    *)
    exit 0 ;; # found it
    esac
    fi
    done
    exit $code # not found

  • jordie April 23, 2013, 7:36 pm

    nice

  • Brian April 23, 2013, 9:26 pm

    Nice work!

  • Ashwin April 23, 2013, 11:49 pm

    Thanks.

  • Ashok April 24, 2013, 2:07 am

    I love this…Thankyou !

  • mohsen zamani April 24, 2013, 2:42 am

    tanx alot . very usefull

  • SureshG April 24, 2013, 2:42 am

    As ususal, simply good.

  • ratna April 26, 2013, 12:00 pm

    explanation with example …its really very good for understanding…Thanx

  • Joan May 9, 2013, 8:19 am

    You can use locate instead of whereis.

  • kaleksanadrov May 17, 2013, 1:03 am

    Thanks!

    Useful and good structured information :)

  • Selvam August 15, 2013, 8:37 pm

    Very useful… Thanks!

  • Patrick January 29, 2014, 1:02 pm

    Nice, I was always confusing those command’s functions. Whatis shows where on the manual that word was mentioned. Whereis gives me options to find binaries, sources and man pages. And Which shows me where exactly is located that command.

    Thank you very much Arora!

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