Do you know what dmidecode command will do?
Ans : Are you going to search in G0ogle about dmidecode? No need to search for it. No need to go any where. Linux provide many help tools to make you familiar with any command. This post is all about these commands/options and they are as follows.
- info command
- man command
- whatis command
- whereis command
- which command
- help command
- –help option
- –usage option
1. info command in Linux/unix
The info command will give a detailed information
The above command will show full help about ls command which is of 10 pages. This will give full information.
2. man command(manual command) in Linux
This will give little bit less descriptive but will provide information which you require, and most of the times each option of a command will be described in one sentence and some times in paragraphs.
Suppose if you want to see multiple commands you can just append commands to man command.
man ls pwd whomai
To exit from first command press “q” without quotes. And continue to next command and repeat “q” to read next command help.
3. whatis command
This will show one line description to a give command. This is similar to “man -k ls”
[email protected]:~$ whatis ls ls (1) - list directory contents LS (6) - display animations aimed to correct users who accidentally enter LS instead of ls .
This command to support multiple commands to append to it.
whatis ls pwd whoami
[email protected]:~$ whatis ls pwd whoami ls (1) - list directory contents LS (6) - display animations aimed to correct users who accidentally enter LS instead of ls . pwd (1) - print name of current/working directory whoami (1) - print effective userid
4. whereis command
This is not a help command but I feel describing this here. This command will show the location of any command and it’s man page location as well.
[email protected]:~$ whereis ls ls: /bin/ls /usr/share/man/man1/ls.1.gz
Even this command to support multiple commands to append to it.
[email protected]:~$ whereis ls pwd whoami ls: /bin/ls /usr/share/man/man1/ls.1.gz pwd: /bin/pwd /usr/include/pwd.h /usr/share/man/man1/pwd.1.gz whoami: /usr/bin/whoami /usr/share/man/man1/whoami.1.gz
5. Which command
This is one more command which will give you just location of the command.
[email protected]:~$ which ls /bin/ls
Even this command too supports multiple commands to append.
[email protected]:~$ which ls pwd whoami /bin/ls /bin/pwd /usr/bin/whoami
6. The help command in Linux
Some times you try to find out info on some commands such cd, pwd etc. But you will see many commands at that time. This is due to the inbuilt commands. So with man, info etc commands you can not get much information about the inbuilt commands. If you want to know what an inbuilt command do, you have to use help command.
[email protected]:~$ help pwd pwd: pwd [-LP] Print the name of the current working directory. Options: -L print the value of $PWD if it names the current working directory -P print the physical directory, without any symbolic links By default, `pwd' behaves as if `-L' were specified. Exit Status: Returns 0 unless an invalid option is given or the current directory cannot be read.
Even this command to appending stuff
[email protected]:~$ help while for if while: while COMMANDS; do COMMANDS; done Execute commands as long as a test succeeds. Expand and execute COMMANDS as long as the final command in the `while' COMMANDS has an exit status of zero. Exit Status: Returns the status of the last command executed. for: for NAME [in WORDS ... ] ; do COMMANDS; done Execute commands for each member in a list. The `for' loop executes a sequence of commands for each member in a list of items. If `in WORDS ...;' is not present, then `in "$@"' is assumed. For each element in WORDS, NAME is set to that element, and the COMMANDS are executed. Exit Status: Returns the status of the last command executed. if: if COMMANDS; then COMMANDS; [ elif COMMANDS; then COMMANDS; ]... [ else COMMANDS; ] fi Execute commands based on conditional. The `if COMMANDS' list is executed. If it's exit status is zero, then the `then COMMANDS' list is executed. Otherwise, each `elif COMMANDS' list is executed in turn, and if it's exit status is zero, the corresponding `then COMMANDS' list is executed and the if command completes. Otherwise, the `else COMMANDS' list is executed, if present. The exit status of the entire construct is the exit status of the last command executed, or zero if no condition tested true. Exit Status: Returns the status of the last command executed.
7. –help option with each command
This option is to give one line discription to each option of the command
[email protected]:~$ passwd --help Usage: passwd [options] [LOGIN]
Options: -a, --all report password status on all accounts -d, --delete delete the password for the named account -e, --expire force expire the password for the named account -h, --help display this help message and exit -k, --keep-tokens change password only if expired -i, --inactive INACTIVE set password inactive after expiration to INACTIVE -l, --lock lock the password of the named account -n, --mindays MIN_DAYS set minimum number of days before password change to MIN_DAYS -q, --quiet quiet mode -r, --repository REPOSITORY change password in REPOSITORY repository -R, --root CHROOT_DIR directory to chroot into -S, --status report password status on the named account -u, --unlock unlock the password of the named account -w, --warndays WARN_DAYS set expiration warning days to WARN_DAYS -x, --maxdays MAX_DAYS set maximum number of days before password change to MAX_DAYS
8. –usage option with each command in Linux
This is similar to –help option available for most of the linux command.
[email protected]:~$ man --usage Usage: man [-dDfkKlwWciIau7tZ?V] [-C FILE] [-R ENCODING] [-L LOCALE] [-m SYSTEM] [-M PATH] [-S LIST] [-s LIST] [-e EXTENSION] [-P PAGER] [-r STRING] [-E ENCODING] [-p STRING] [-T[DEVICE]] [-H[BROWSER]] [-X[RESOLUTION]] [--config-file=FILE] [--debug] [--default] [--warnings[=WARNINGS]] [--whatis] [--apropos] [--global-apropos] [--local-file] [--where] [--path] [--location] [--where-cat] [--location-cat] [--catman] [--recode=ENCODING] [--locale=LOCALE] [--systems=SYSTEM] [--manpath=PATH] [--sections=LIST] [--extension=EXTENSION] [--ignore-case] [--match-case] [--regex] [--wildcard] [--names-only] [--all] [--update] [--no-subpages] [--pager=PAGER] [--prompt=STRING] [--ascii] [--encoding=ENCODING] [--no-hyphenation] [--nh] [--no-justification] [--nj] [--preprocessor=STRING] [--troff] [--troff-device[=DEVICE]] [--html[=BROWSER]] [--gxditview[=RESOLUTION]] [--ditroff] [--help] [--usage] [--version] [SECTION] PAGE...
Please remember –help or –usage may not work with some commands.