More Linux CLI Commands

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Linux provides a CLI (Command Line Interface) to communicate with the OS. Here are the most basic of the Linux Commands.

1. pwd

This command Displays the current working directory of the terminal.

syntax:

$ pwd

2. echo

This command writes its arguments to standard output.

syntax:

$ echo "<text>"

3. su

This command is used to switch to root-user so that superuser permissions can be used to execute commands.

syntax:

$ su

4. su <username>

This command is used to switch to a different user whose name is passed as the argument.

syntax:

$ su <username>

5. sudo

This command executes only that command with root/ superuser privileges.

syntax:

$ sudo <command>

Command	Explanation
sudo useradd <username>	Adding a new user
sudo passwd <username>	Setting a password for the new user
sudo userdel <username>	Deleting the user
sudo groupadd <groupname>	Adding a new group
sudo groupdel <groupname>	Deleting the  group
sudo usermod -g <groupname> <username>	Adding a user to a primary group

6. clear

This command is used to clear the terminal screen. Contents will not actually be deleted in this case, only scrolled down. You can also clear the screen by pressing Ctrl+L on the keyboard.

syntax:

$ clear

Linux Commands: Working with Files

7. cp

This command copies files and directories. A copy of the file/directory copied, still remains in the working directory.

syntax:

$ cp <flag> {filename} /pathname/

Command	Explanation
cp -i	Enters interactive mode; CLI asks before overwriting files
cp -n	Does not overwrite the file
cp -u	Updates the destination file only when the source file is different from the destination file
cp -R	Recursive copy for copying directories; Copies even hidden files
cp -v	Verbose; Prints informative messages

8. mv

This command moves files and directories from one directory to another. The file/directory once moved, is deleted from the working directory.

syntax:

$ mv <flag> {filename} /pathname/

Command	Explanation
mv -i	Enters interactive mode; CLI asks before overwriting files
mv -u	Updates the destination file only when the source file is different from the destination file
mv -v	Verbose; Prints source and destination files

9. rm

This command removes files from a directory. By default, the rm command does not remove directories. Once removed, the contents of a file cannot be recovered.

syntax:

$ rm <flag> {filename}

Command	Explanation
rm –r	Removes even non-empty directories.
rm –rp	Removes non-empty directories including parent and subdirectories.

10. grep

This command is used to search for a particular string/ word in a text file. This is similar to “Ctrl+F”, but executed via a CLI.

syntax:

$ grep <flag or element_to_search> {filename}

Command	Explanation
grep -i	Returns the results for case insensitive strings
grep -n	Returns the matching strings along with their line number
grep -v	Returns the result of lines not matching the search string
grep -c	Returns the number of lines in which the results matched the search string

11. cat

This command can read, modify or concatenate text files. It also displays file contents.

syntax:

$ cat <flag> {filename}

Command	Explanation
cat -b	This is used to add line numbers to non-blank lines
cat -n	This is used to add line numbers to all lines
cat -s	This is used to squeeze blank lines into one line
cat –E	Show $ at the end of line

Linux Commands: Working with Directories

12. ls

This command lists all the contents in the current working directory.

syntax:

$ ls <flag>

Command	Explanation
ls <path name>	By specifying the path after ls, the content in that path will be displayed
ls –l	Using ‘l’ flag, lists all the contents along with its owner settings, permissions & time stamp (long format)
ls –a	Using ‘a’ flag, lists all the hidden contents in the specified directory
ls –author	Using ‘–author’ flag, lists the contents in the specified directory along with its owner
ls –S	Using ‘a’ flag, sorts and lists all the contents in the specified directory by size
ls .html	Using ‘’ flag, lists only the contents in the directory of a particular format
ls –lS > file.txt	Using ‘>’ flag, copies the result of ls command into a text file

13. cd

This command is used to change the current working directory of the user.

syntax:

$ cd /pathname/

Command	Explanation
cd ~	This command also changes the directory to home directory
cd /	Changes the directory to root directory
cd ..	Changes the directory to its parent directory
cd ‘xx yy’	We specify the folder name in inverted commas because there is a space in the folder name

14. sort

This command sorts the results of a search either alphabetically or numerically. Files, file contents and directories can be sorted using this command.

syntax:

$ sort <flag> {filename}

Command	Explanation
sort -r	the flag returns the results in reverse order;
sort -f	the flag does case insensitive sorting
sort -n	the flag returns the results as per numerical order

15. mkdir

This command is used to create a new directory.

syntax:

$ mkdir <flag> {directoryname} /pathname/

Command	Explanation
mkdir -p	Creates both a new parent directory and a sub-directory
mkdir –p  <filename1>/{f1,f2,f3}	This is used to create multiple subdirectories inside the new parent directory

16. rmdir

This command is used to remove a specified directory. Although by default, it can only remove an empty directory, there are flags which can be deployed to delete the non-empty directories as well.

syntax:

$ rmdir <flag> {directoryname}

Command	Explanation
rmdir –p	Removes both the parent and child directory
rmdir –pv	Removes all the parent and subdirectories along with the verbose.

Linux Commands: Working with User Permissions

17. chmod

This command is used to change the access permissions of files and directories. Consider the example below.

On trying to run the newly created file named chmodtest.sh, an error is thrown. After modifying the permissions of the file using the said Linux command, it turns executable.

syntax:

$ chmod <permissions of user,group,others> {filename}

The permissions associated with each digit is as follows.

Number	read	write	execute
0	–	–	–
1	–	–	yes
2	–	yes	–
3	–	yes	yes
4	yes	–	–
5	yes	–	yes
6	yes	yes	–
7	yes	yes	yes

Linux Commands: Installing Packages

Stable versions of most software’s will already be available in Linux repositories. Here are the Linux Commands to install them.

18. install packages

For an RHEL based system;

syntax:

$ sudo yum install package-name

For a Debian based system;

syntax:

$ sudo apt-get install package-name

For a Fedora based system;

syntax:

$ sudo dnf install package-name

Linux Commands: Working with Zipped Files

When you download a package from the internet, the downloaded file comes in compressed form. Here are a few commands to decompress and compress files in Linux.

19. tar

The following command is used to zip files of .tar format.

syntax:

$ tar –cvf tar-filename source-folder-name

The following command is used to unzip files of .tar format.

syntax:

$ tar –xvf tar-file-name

Linux Commands: Working with Secure Shell For Remote Machine Access

20. ssh

This command refers to a cryptographic network protocol for operating network services securely over an unsecured network. Typical use-cases include remote command-line execution, but any network service can be secured with SSH.

The following command, on running at the slave node, will give remote access to the master.

syntax:

$ ssh <master's ip>

The following command, on running at the master, will give remote access to the slave node.

syntax:

$ ssh <slave's ip>

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