Single letter options usually preceded by - Can be passed as -a -b -c or -abc
Full word options usually preceded by -- Example: --help
Arguments are file names or other data needed by the command
Multiple commands can be separated by semicolon (;) mkdir backups; cp *.txt backups/`
Some Simple Commands
Date - Display date and time
date command prints system date and time.
The format is configurable via an optional formatting string (see options with date --help)
Cal - Display Calendar
cal command prints an ASCII calendar of the current month.
When single numeric argument is passed to the cal command, cal command prints the given year calendar.
For example: cal 06 will print the calendar for the year 0006, not the year 2006.
When a month and year is passed as argument to the cal command, cal command prints the particular month calendar.
Don’t try to memorise everythings!
Many levels of help
1. whatis comand
Display short discriptions of commands.
whatis command uses a database that is updated nightly, so often not available immediately after install.
Generate whatis database without waiting for automatic update, run makewhatis command as root user.
2. --help option
Just knowing what a command does is not always enough.
In order to use a command effectively you need to know what options and arguments it accepts (the syntax of the command).
Most commands have a --help options, but not all the commands have --help options.
The command --help option Display usage summary and argument list.
Reading Usage Summaries
Arguments in  are optional.
Arguments in <> or CAPS are variables.
Text followed by … represent a list.
x|y|z means x or y or z.
-abc means any mix of -a, -b or -c.
3. The man command:
Almost every commands as well as most of the configuration files and several developer’s libraries on Linux system has an associated man pages, which provides more through documentations than the command --help options.
The man pages normally contains the following sections
The collection of all the man pages on a system is called Linux Manual.
The Linux Manual is divided into several sections, each of which covers a particular topics, and every man page is associated with exactly one of these sections.
The Linux Manual sections are:
Often, Linux commands, calls, and files are referenced by a name followed by manual section number in parentheses.
Navigating man pages
Navigate with arrows, PgUp, PgDn
/text searches for text
n/N goes to next/previous match
q quits man page
Searching Linux Manual
Suppose you do not know the name of command you are looking for, in this case you can perform keyword search.
To perform keyword search its uses whatis database.
4. The info command
Similar to man command, but often more in-depth.
Run info command without arguments, list all the info pages.
The structure of info pages are looks like a website.
Each page is divided into nodes.
Links to nodes are precededby *.
Navigating info pages
Navigate with arrows, PgUp, PgDn
Tab moves to next link
Enter follows the selected link
s text searches for text (default: last search)
n/p /u/l goes to next/previous/up-one/last node
q quits info page
NOTE!: If you prefer the navigation keys used by man commands, such as / n and N, you can start info command with –vi-keys argument. Example: info –vi-keys [command]
5. Extended Documentation
The /usr/share/doc directory contains the documentations that does not fit the length or the format of a man and info pages.
The /usr/share/doc is a location of documents that does not fit elsewhere.