Basic commands:

The help option:

Most commands have a --help option, which prints a short message about how to use the command and exits:

Syntax


$ command_name --help

Example


$ cd --help

Navigating manual pages:

A man or manual page is a form of documentation that explains what the command does, examples of how we run the command, and what arguments it accepts.
The man command is used to display the manual page of a given command.

Syntax


$ man command_name

Example


$ man cd

Currently logged-in users:

who is a command-line utility that prints a list of currently logged in users. It can also show the current run level, time of the last system boot, and more. The basic syntax for the who command is as follows:

Example


$ who

Output


root     pts/0        2020-11-17 20:10 (10.10.0.2)
user1    pts/1        2020-11-17 20:11 (10.10.0.8)

Each line contains four fields separated by one or more spaces:

The name of the logged user.
The user’s terminal. Here it is pts (Pseudo Terminal Session) which is when we are running Linux terminal from a server over TELNET. It could also be tty (Terminal for Text only) which is when we run Linux terminal on the real hardware.
The time when the user logged in.
The hostname or IP address from where the user is logged in.

If you want to print the column headings, add the -H option:

Example:


$ who –H

Output:


NAME      LINE         TIME             COMMENT
root      pts/0        2020-11-17 20:10 (10.10.0.2)
user1     pts/1        2020-11-17 20:11 (10.10.0.8)

who accepts two non-option arguments. When invoked with two arguments the command prints information only about the terminal associated with the current user. The same output is displayed when the -m option is used.
You can use any two arguments:

Example:


$ who am i
[or]
$ who –m

Both the commands will print the same information:

Output:


user1  pts/1        2020-11-17 20:11 (10.10.0.8)

echo command in Linux:

The echo command is one of the most basic and frequently used commands in Linux. The arguments passed to echo are printed to the standard output.

echo is commonly used in shell scripts to display a message or output the results of other commands.

Display a line of text on standard output.
Example:
$ echo Hello, World!
Output:
Hello, World!

Display a line of text containing a double quote.
Example:
$ echo 'Hello "World"'
Output:
Hello "World"

Display a line of text containing a single quote.
Example:
$ echo "I'm a Linux user."
Output:
I'm a Linux user.

Display a message containing special characters.
Example:
$ echo -e "India is great.\n\t- Sachin"
Output:
India is great. - Sachin

Pattern matching characters.
Example:
$ echo The PHP files are: *.php
Output:
The PHP files are: index.php contact.php functions.php

Redirect to a file.
Example:
$ echo -e 'The only true wisdom is in knowing you know nothing.\nSocrates' >> /tmp/file.txt

Current Working Directory:

The current working directory is the directory in which the user is currently working. Each time we interact with our command prompt, we are working within a directory.
We use the pwd command to find out what directory we are currently in:

Example


$ pwd

Output


/home/user1

Changing directory:

The cd (“change directory”) command is used to change the current working directory in Linux. When used without any argument, cd will take us to our home directory:

Example


$ cd

To change to a directory, we can use its absolute or relative pathname.

Relative pathname:Assuming that the directory dir1 exists in the directory from which we run the command, we can navigate to it by using the relative path to the directory:
Example
$ cd dir1

Absolute pathname:We can also navigate to a directory by using its absolute path:
Example
$ cd /home/apple/Downloads