5 Methods to Get Quick Help on Linux Commands

Before heading to Google to get help on a particular Unix command, try the following methods, which will give you a comprehensive help on Unix commands.

1. Using apropos to search man pages

Use apropos to search man pages for available Unix commands on a specific functionality.

$ apropos -r REGEXofUNIXCOMMAND or Description.

About apropos command from the man page:

       apropos searches a set of database files containing short
       descriptions of system commands for keywords and displays
       the result on the standard output.

Following example displays all the available grep related commands using apropos.

$ apropos grep
bzegrep (1)          - search possibly bzip2 compressed files for a regular expression
bzfgrep (1)          - search possibly bzip2 compressed files for a regular expression
bzgrep (1)           - search possibly bzip2 compressed files for a regular expression
egrep (1)            - print lines matching a pattern
fgrep (1)            - print lines matching a pattern
grep (1)             - print lines matching a pattern
pgrep (1)            - look up or signal processes based on name and other attributes
rgrep (1)            - print lines matching a pattern
zegrep (1)           - search possibly compressed files for a regular expression
zfgrep (1)           - search possibly compressed files for a regular expression
zgrep (1)            - search possibly compressed files for a regular expression
zipgrep (1)          - search files in a ZIP archive for lines matching a pattern

2. Read man page of the command

This is the easy and most effective method to get quick help on any Unix command. I’ve seen lot of people (especially newbies) getting bored reading the man pages.

While Unix man pages might not have lot of practical examples, it does explain all the options available for a command in a detailed manner.

$ man UNIXCOMMAND

$ man tar

If you don’t know the exact command name for a specific functionality, use man -k option to locate the command.

The below example lists all the available commands that has the word “compression” in the description.

$ man -k REGEX or UNIXCOMMAND

$ man -k compression
bzip2               (rpm) - A file compression utility.
gzip                (rpm) - The GNU data compression program.
zip                 (rpm) - A file compression and packaging utility compatible with PKZIP.
zlib                 (3)  - compression/decompression library
zlib                (rpm) - The zlib compression and decompression library.

3. Display Single Line Description About a Unix Command

To display a single line description about the command, you can use whatis command.

$ whatis UNIXCOMMAND

About whatis command from the man page:

       whatis  searches a set of database files containing short descriptions
       of system commands for keywords and displays the result on the
       standard output.  Only complete word  matches are displayed.

The following example displays high level single line information about the cron command.

$ whatis cron
cron (8)             - daemon to execute scheduled commands (Vixie Cron)

4. Use -h or –help option of the command itself

Sometimes you may know the functionality of a command very well, but cannot recollect all the available options for a specific command. Use -h option of the command to review all available options of the command.

$ UNIXCOMMAND -h

Following example will display a quick help on netstat command

$ netstat -h

5. Read Info Documents using Unix info Command

When you are not able to find the required information from the Unix man page, try the info documents using the Unix info command as shown below.

$ info UNIXCOMMAND

$ info sed

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