Vamshi Krishna Santhapuri

The Linux find command utility is a powerful command in locating the files and directories at system wide level, the

The basic syntax of find command is very straight forward. The number of filters and types of options you choose while forming the find command determines and complexity of the operation and is directly proportional to the run time of the command.

Lets examine the general syntax of Linux find command line utility

$ find [path] [Options/filters] [expression]

How to Find all the files that are modified within 1 day.

$ find . -mtime -1

Use find command to find all the files that are modified within last x Minutes

$ find . -mmin -360

How to Find all the files that are created within given Minutes

$ find . -cmin -360

How to Find all the files under a specific size on the filesystem.

$ find . -type f -size -100G

NOTE: the - will find the files including and under the mentioned size

How to find really big size files with a given size using Linux Find Command.

$ find . -type f -size +100G

NOTE: the + will find the files exceeding the mentioned size

How to Find all the files with a pattern match using Find command?

vamshi.santhapuri@linux-pc:~/Linux/Programs> find *.py
my_program.py
myProgram.py
My_program.py

OutPut Demonstrated:

vamshi@linuxcent:~/Linux/Programs> ls -l
total 0
-rwxr-xr-x 1 vamshi users 0 Apr 8 16:33 my_program.py
-rwxr-xr-x 1 vamshi users 0 Apr 8 16:32 myProgram.py
-rwxr-xr-x 1 vamshi users 0 Apr 8 16:32 My_program.py ex

 

Find Files Based on file-type using option -type

Find only the regular file type

$ sudo find / -type f -print

Find only the Directory

$ sudo find / -type d -print

Lets see some special file formats like character files as in network level files and block files as in storage device file type.

$ sudo find /dev/ -type b -print
/dev/sdb8
/dev/sdb7
/dev/sdb6
/dev/sdb5
/dev/sdb4
/dev/sdb1
/dev/sdb
/dev/sda6
/dev/sda5

How to find empty files and Directories in Linux using Find command?

$ find . -empty # Finds all files and directories that are empty
$ find . -type f -empty #Find onlt empty files
$ find . -type d -empty #Find only empty Directories

How to Find all the hidden files and directories using Find command

You can also add the type flag as required

$ find . -name ".*" //Prints all the files and directories that are hidden

Find the character stream files and identify them yourselves.

$ sudo find / -type c -print

 

How to exclude some files or directories while using the find command?

The negation Operator ! in find command line

[vamshi@linuxcent ~]$ find / -type d  ! -path /mount ! -path /mnt/3TB/

How to find the files with .py extension and then setting the execute permission on them ?

-exec is a special builtin option which takes the specified command on the selected files

[vamshi@linuxcent ~]$ find *.py -exec chmod +x {} \;

A practical example of Finding and Deleting Big size files using Find Command

We Demonstrate a Big thread dump file that we generated in our Test environment by finding it on our server and then deleting it.

[vamshi@linuxcent ~]$ find /var -type f -size +100G -exec rm {} \;

 

To find the files with matching file permissions

[vamshi@linuxcent ~]$ sudo find / -type f -perm 0600 -print

More complex find operations can be performed by combining the negation operator and by excluding the certain mount points and using the logical AND OR operators.

For example:

sudo find / -xdev -type d \( -perm -0002 -a ! -perm -1000 \) -exec ls -ld {} \;

Ignore case using the find command

The filter -iname enables the find to perform case insesitive search.

[vamshi@node02 Linux-blog]$ find . -iname "rEadMe*" 
./Debian-Distro/README-Debian-Distro
./OpenSuse-Distro/README-Opensuse-Distro
./README
./Redhat-Distro/Centos/README-CentOS
./Redhat-Distro/README-Redhat-Distro

How to use Maxdepth Option in the find command to explore the directory depth?

[vamshi@node02 Linux-blog]$ find . -maxdepth 1 -name "README*" 
./README

By using find command filter option -maxdepth Now we can extract the results based on the one level deeper subdirectory, which is demonstrated as follows:

[vamshi@node02 Linux-blog]$ find . -maxdepth 2 -name "README*" 
./Debian-Distro/README-Debian-Distro
./OpenSuse-Distro/README-Opensuse-Distro
./README
./Redhat-Distro/README-Redhat-Distro

How to use mindepth Option in the find command to restrict the results based on the subdirectory depth?

The -mindepth filter option restricts the find command search to nth subdirectory level from the given path.

[vamshi@node02 Linux-blog]$ find . -mindepth 3 -name "README*" 
./Redhat-Distro/Centos/README-CentOS

 

The grep command is one of the most essential commands in Unix/Linux ecosystem, It is used to extract match and find the occurrence of string literals and patterns among the text files.

In this section we will focus on the important scenarios and provide the realtime explanation about the Various Grep command options offered in linux command line.

We now have a text file with Following content.

Below is the content of the file called intro.txt.

[vamshi@linuxcent grep]$ cat intro.txt
the first line is in lower case
THE SECOND LINE IS IN UPPER CASE


There following are Most popular Linux server Distributions:
1) Redhat Enterprise Linux
2) Ubuntu
3) Centos
4) Debian
5) SUSE Linux Enterprise Server
This is a Demonstration of Linux grep command

Let’s start with search of a string pattern in the given file

The grep command sample search syntax is

$ grep “string pattern” <filename>

$ cat < filename | * > | grep "string pattern"

Lets see the Demonstration

[vamshi@linuxcent grep]$ grep "Linux" intro.txt
There following are Most popular Linux server Distributions:
1) Redhat Enterprise Linux
5) SUSE Linux Enterprise Server
This is a Demonstration of Linux grep command

Searching for a pattern on multiple files using grep command

Lets see the Demonstration

[vamshi@linuxcent grep]$ grep "Linux" intro.txt intro-demo.txt
intro.txt:There following are Most popular Linux server Distributions:
intro.txt:1) Redhat Enterprise Linux
intro.txt:5) SUSE Linux Enterprise Server
intro.txt:This is a Demonstration of Linux grep command
intro-demo.txt:There following are Most popular Linux server Distributions:
intro-demo.txt:1) Redhat Enterprise Linux
intro-demo.txt:5) SUSE Linux Enterprise Server
intro-demo.txt:This is a Demonstration of Linux grep command

 

How to print the sequence number of matched pattern in file using Grep command in Linux?

Print the sequence number of lines that contain the matched string pattern can be achieved using -n Option:

[vamshi@linuxcent grep]$ grep -n "Linux" intro.txt
4:There following are Most popular Linux server Distributions:
5:1) Redhat Enterprise Linux
9:5) SUSE Linux Enterprise Server
11:This is a Demonstration of Linux grep command

The -b Option prints the subsequent starting offset index of the matching word from the lines within the given filename.

[vamshi@linuxcent grep]$ grep -b "Linux" intro.txt
66:There following are Most popular Linux server Distributions:
127:1) Redhat Enterprise Linux
184:5) SUSE Linux Enterprise Server
217:This is a Demonstration of Linux grep command

So far we have seen only the matching string pattern, but if you want to find the occurance of particular word then use grep -w Option

Lets us see the Demonstration below:

[vamshi@linuxcent grep]$ grep -w "Cent" intro.txt

And As expected here we have not seen any occurrence of the word Cent from the file although the word Centos was present, But it didnt match because we used -w option to match the word Cent.

But when we grep for the Word Linux then we can see the exact occurrence of the word and the matching lines are printed.

[vamshi@linuxcent grep]$ grep -w "Linux" intro.txt
There following are Most popular Linux server Distributions:
1) Redhat Enterprise Linux
5) SUSE Linux Enterprise Server
This is a Demonstration of Linux grep command

This can be used in conjunction with -o prints only completely matched word string pattern.

[vamshi@linuxcent grep]$ grep -w -o "Linux" intro.txt
Linux
Linux
Linux
Linux

How to use the Invert Option in Linux grep command

The -v option prints all the lines not matching the given string pattern.

[vamshi@linuxcent grep]$ grep -v "Linux" intro.txt
the first line is in lower case
THE SECOND LINE IS IN UPPER CASE


2) Ubuntu
3) Centos
4) Debian

 

How to print the names of all the files matching the string pattern using Linux Grep command.

Using the -l Option of grep command will print all the file names containing the matching string pattern/string literal

[vamshi@node02 grep]$ grep -l Linux *
intro-demo.txt
intro.txt

How to get the number of Count Matches using Grep command ?

In Linux Grep command we can use the Option -c to get the total occurance Count of the matching pattern/string

Lets see the Demonstration below

[vamshi@linuxcent grep]$ grep -c "Linux" intro.txt
4

How to Exclude specific Directories while searching with grep command ?

The --exclude-dir="Some Directory name" options skips the contents of the mention directory Lets see the Demonstration:

$ grep -w -E "data" * -R --exclude-dir="backup" --exclude-dir="adb-fastboot" --exclude-dir="IntelliJ-IDEA"

How to use Linux Grep commmand to ignore the case  OR perform Case Insensitive search ?

Linux Grep Command offers the -i to skip the case and perform the search.

[vamshi@linuxcent grep]$ grep -i Cent intro.txt
3)Centos

Lets search for the Work Upper from the file with -i option

[vamshi@linuxcent grep]$ grep Upper -i intro-demo.txt
THE SECOND LINE IS IN UPPER CASE

How to Grep for the lines before and After the pattern occurrence in a file

We can use the below options in Linux Grep command to extract the N number of lines matching the containing pattern before/After from the given file.. Lets look at the Options in detail

Generic Syntax:

grep -<A|B|C> “string pattern” filename*

Lets see the Demonstration as follows:

-A: Prints N number of lines After the pattern match and the line containing the match

[vamshi@linuxcent grep]$  grep -A2 docker /etc/passwd
dockerroot:x:996:992:Docker User:/var/lib/docker:/sbin/nologin
mysql:x:27:27:MariaDB Server:/var/lib/mysql:/sbin/nologin
ntp:x:38:38::/etc/ntp:/sbin/nologin

-B: Prints N number of lines Before the pattern match and the line containing the match

[vamshi@linuxcent grep]$  grep -B2 docker /etc/passwd
apache:x:48:48:Apache:/usr/share/httpd:/sbin/nologin
builduser1:x:1002:1002::/home/builduser1:/bin/bash
dockerroot:x:996:992:Docker User:/var/lib/docker:/sbin/nologin

-C: Prints the line Containing the pattern and the N number of lines Before and After

[vamshi@linuxcent grep]$ grep -C2 docker /etc/passwd
apache:x:48:48:Apache:/usr/share/httpd:/sbin/nologin
builduser1:x:1002:1002::/home/builduser1:/bin/bash
dockerroot:x:996:992:Docker User:/var/lib/docker:/sbin/nologin
mysql:x:27:27:MariaDB Server:/var/lib/mysql:/sbin/nologin
ntp:x:38:38::/etc/ntp:/sbin/nologin

Linux Grep command using the Regular Expression (regex) search pattern

How to use the Special Meta-characters in Grep Command

The Special Meta-Character ^ (caret) symbol to match expression at the start of a line.
Practical examples of grep command using meta-characters are as follows:

[vamshi@linuxcent grep]$ grep ^root /etc/services
rootd           1094/tcp                # ROOTD
rootd           1094/udp                # ROOTD

$ (dollar) symbol to match expression at the end of a line

[vamshi@linuxcent grep]$ grep "bash$" /etc/passwd
root:x:0:0:root:/root:/bin/bash
vagrant:x:1000:1000:vagrant:/home/vagrant:/bin/bash
vamshi:x:1001:1001::/home/vamshi:/bin/bash
jenkins:x:997:994:Jenkins Automation Server:/var/lib/jenkins:/bin/bash
builduser1:x:1002:1002::/home/builduser1:/bin/bash
linuxcent:x:1003:1004::/home/linuxcent:/bin/bash

Another Bonus regex for evading Empty lines from a text file using the Meta-characters ^ Carat and $ Dollar Symbols.

[vamshi@node02 grep]$ grep -Ev "^$" intro.txt
the first line is in lower case
THE SECOND LINE IS IN UPPER CASE
There following are Most popular Linux server Distributions:
1) Redhat Enterprise Linux
2) Ubuntu
3) Centos
4) Debian
5) SUSE Linux Enterprise Server
This is a Demonstration of Linux grep command

As the result of the above command observed Empty lines in our text file are now excluded with the inverted matching of Empty line pattern expression.

Digit Matching operation using Linux Grep Command

The Grep command Option -P offers the perl-regex pattern matching to perform some of the tricky pattern matching conditions, Lets see the Demonstration.

[vamshi@linuxcent grep]$ grep -P "[\W][\d][\d]/" /etc/services

Now we Demonstrate Numerical pattern matching in the following ways to match the exact occurrence of IPv4 address

[vamshi@linuxcent grep]$ ip a |grep -E "[0-9].[0-9].[0-9].[0-9]"
inet 127.0.0.1/8 scope host lo
inet 10.100.0.20/24 brd 10.100.0.255 scope global noprefixroute eth1

The similar result can be extracted using -P, Demonstrated as below:

[vamshi@linuxcent grep]$ ip a  | grep -P "[\d].[\d].[\d].[\d]"
inet 127.0.0.1/8 scope host lo
inet 10.100.0.20/24 brd 10.100.0.255 scope global noprefixroute eth1

Highlighting the Search patterns with Color codes

If you want to highlight the search pattern from the output we can make use of Color code Option is grep

[vamshi@linuxcent ~]$ ps -ef |grep java --color=yes

 

grep command and the Meta-characters with practical examples

In the Extended Regular Expression the metacharacters ?, \+, \{,  \|, \(, and \) enhances and takes the search string to manifest into a rich pattern

The square brackets [/code][ ][/code] includes a list of characters and it matches a single character in the list. Within the bracket, we can specify a  range, like [a-z] [0-9] [abcd], But it only matches a single character in the give list range.
The brackets can contain the carat ^ or the $ symbols and can be globbed with the wildcard characters for finding the repetitive pattern.

Here we shall see the demonstration of a few metacharacters conjunction into a single grep command

Using the Infix Operator | with the meta-characters

$ dmesg -H | egrep '(s|h)d[a-z]'

A quick practical look at the dmesg to find about the errors and warnings using grep command.

$ dmesg -H | grep -Ei “error|warn”

How to find the exact work match for the word error or err with a blank white space at the start of the word from dmesg?
$ dmesg -H | grep -Ei “(er)[r]{1,2}(or)”
$ dmesg -H | grep -Ei “(\We)[r]+(or)|(\Werr)”

Explanation: The grep search metacharacter regular expression matches the occurring of the string literals “error” with the minimum 1 time occurrence (error) of literal r and maximum 2 times.

The output only prints lines containing the word “error“ in a case insensitive grep search.

 

Another great practical example here we apply the same logic to enhance the metacharacter regex pattern to search for the occurrence of error with but without a trailing colon “:” symbol

dmesg -H | grep -Ei “(error)[:]{0}”

 

The Linux command utility chmod is used to set permissions on files and directories

The command chmod, or Change Mode, is widely used to modify the access permissions of files and directories, This facilitates the users to keep the data secure and properly organized.
There are three types the file permissions can be modified using chmod command:

1) Symblolic Notation

2) Octal Notation

3) Reference operator

The Owners, Groups and Others have different permissions to access a particular file.
Lets see the Sample syntax of chmod

$ chmod [option] [mode] < file | directory>

The Users categories are symbolically represented as

-u is used for the User/Owner

g is used for the Group

o is used for the Others

The Permission modes used to modify the Read, Write and Execute permissions respectively on a file or Directory and are symbolically represented as follows

r is for Read permission

w is for Write permission

x is for Execute permission

The Octal notation is simpler interms of representation and execution with r=4 w=2 x=1 total adding up to numerical aggregate value of 7 taking the place holders of Owner(-u) Group(-g) Others(-o) respectively.

Lets see the file permissions for a sample file with complete access to every user category i.e owner, group and others, Meaning that any person who has access to the file can modify,execute(run) or delete the newfile.txt

[vamshi@node02 linuxcent]$ ls -l file.txt
-rwxrwxrwx. 1 vamshi vamshi 3 Apr 10 19:13 file.txt

From the above listed permissions we would like to release the “others” from writing this file but only limit them to read it.

The command will be to delete the Write permissions from others:

[vamshi@linuxcent ~]$ $ chmod o-w file.txt
[vamshi@linuxcent ~]$ ls -l file.txt
-rwxrwxr-x. 1 vamshi vamshi 3 Apr 10 19:13 file.txt

We use the + and - operators to provide the Read,Write and Execute permissions to user categories, It’s Demonstrated as follows:

[vamshi@node02 linuxcent]$ chmod og-rw file.txt
[vamshi@node02 linuxcent]$ ls -l file.txt
-rwx------. 1 vamshi vamshi 3 Apr 10 20:23 file.txt

Combining options such read operation for other and group, write for group and execute permission being removed for owner.

[vamshi@node02 linuxcent]$ chmod og+r,g+w,u-x file.txt

[vamshi@node02 linuxcent]$ ls -l file.txt
-rw-rw-r--. 1 vamshi vamshi 3 Apr 10 20:23 file.txt

Creating a new file newfile.txt and working with it

[vamshi@node02 linuxcent]$ echo "Welcome to LinuxCent" > newfile.txt

Here are the file’s permissions when it’s newly created. It is resultant of the umask

Lets look at a Linux practical example to setup only execute permission for all the user categories

$ chmod +x  /etc/profile.d/java-path.sh

Listing out the System defined Default umask in Symbolic notation.

The Default Umask permissions can be demonstrated as below:

[vamshi@node02 linuxcent]$ umask -S
u=rwx,g=rwx,o=rx

Umask in Octal Notation as below:

[vamshi@node02 linuxcent]$ umask
0002

Now the new lets see the file permissions:

[vamshi@node02 linuxcent]$ ls -l newfile.txt
-rw-rw-r--. 1 vamshi vamshi 21 Apr 10 19:49 newfile.txt

This is the inverse notation of the umask Octal value(002) set at the system wide and our file has the 664 Octal Notation.

The Octal mode of Permissions

These permissions carry a numerical value all adding up to a sum of 4 and categorized as follows:

r=4 w=2 x=1

For Example chmod 754 file1.txt

[vamshi@node02 linuxcent]$ ls -lth newfile.txt
-rwxr-xr--. 1 vamshi vamshi 3 Apr 10 19:13 newfile.txt

How to apply reference permissions in Linux using chmod ?

We shall be using the option --reference which takes the reference from the existing file and applies the permission

Lets see the demonstration below:

vamshi@linuxcent ~]$ ls -l anotherfile.txt
-rwxrwx---. 1 vamshi vamshi  33 Apr 8 19:52 anotherfile.txt

vamshi@linuxcent ~]$ chmod --reference=anotherfile.txt newfile.txt

[vamshi@linuxcent ~ ]$ ls -l newfile.txt 
-rwxrwx---. 1 vamshi vamshi 21 Apr 10 19:49 newfile.txt

With this reference operator, the nexfile.txt permissions are modified identical to anotherfile.txt

 

Do you want to learn the Linux commands? If yes, then you are in the right place. There are uncountable commands in Linux. Generally, we use some of the Linux commands from the Linux commands cheat sheet regularly to perform the common tasks.

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• Basic Linux Commands
• File Permission Commands
• Environment Variables Command
• User Management Commands of Linux
• Networking Commands
• Process Commands
• VI Editing Commands
• Other Linux Commands

You can also learn Google Sheets Tips – New Google Spreadsheet Hacks, Tricks with Examples

Types of Linux Commands

All the Linux commands are categorized into 7 different types. They are Basic Linux commands, File permission commands, Environment variables commands, User management commands, Networking commands, Process commands, VI Editing commands, Other Commands.

We are giving a detailed explanation for each and every Linux command with their examples for easy learning in the below sections. Have a look at them and follow them. Check the actual description of each Linux command in their manual page.

Basic Linux Commands

• ls command:

It is used to list all files and directories of a directory. The ‘-l’ option gives the long listing format. Its syntax is $ ls [options] [file|dir]

Example: $ ls -l samplefile

• ls-R command:

It gives the lists files in subdirectories. List recursively directory tree and syntax is $ ls -R [options] [file|dir]

Example: $ ls -R samplefile

• ls -a Command:

It lists all files including hidden files starting with’.’ Its syntax is $ ls -a [options] [file|dir]

• ls -al Command:

It lists all files details and directories with detailed information like permissions, size, owner, etc. Syntax is $ ls -al [options] [file|dir]

• cd or cd ~ Command:

This command will navigate to the home directory or change the directory. Its syntax is $ cd [directory]

Example: $ cd Directory1

• cd .. Command:

It moves one level up. Syntax is $ cd . . [directory]

• cd Command:

Use this command to change to a particular directory. Its syntax is $ cd [directory]

Example: $ cd directory1

• cd / Command:

This command will move to the root directory. Syntax is $ cd /

• cat filename Command:

Create a new file using this command in Linux. Its syntax is $ cat filename.

Example: $ cat filename1

• cat filename Command:

It displays the content in that particular file. The syntax is $ cat filename.

Example: $ cat filename1.

• cat file1 file2 file3 Command:

It combines two files namely file1 and file2 and stores the output in a new file called file3. Its syntax is $ cat file1 file2 file3.

Example: $ cat add multiply arithmetic.

• mv file “new file path” Command:

It moves the files to the new location. Syntax is $ mv file “new file path”.

Example: $ mv add “E:/Arithmeticopeartions/”.

• mv filename new_file_name Command:

It renames or changes the file name to a new file name. Syntax is $ mv filename new_file_name.

Example: $ mv add sum

• sudo Command:

sudo command allows a permitted user to run a command as root or another user. It runs commands in superuser mode. The syntax is $ sudo filename option

Example: $ sudo apt update

• rm Command:

It is used to remove the files or directories. Syntax is $ rm filename or $ rm directory

Examples: $ rm sum and $ rm mydrive

• man Command:

It is used to view the online reference manual pages for the commands or programs. It provides the help information of any commands. Its syntax is $ man commandname

Example: $ man cd

• history Command:

It produces the list of previously used commands and gets the all past commands types in the current terminal session. The syntax is $ history

• clear Command:

clear command is helpful to clear the terminal screen. The syntax is $ clear

• mkdir directoryname Command:

It creates a new directory in the present working directory or at any specific path. Syntax is $ mkdir directoryname

Example: $ mkdir new_directory

$ mkdir -p new_directory: Here -p option is used to override the already available directory.

• rmdir Command:

It helps to remove/ delete the empty directories. Syntax is $ rmdir [directory_name]

Example: $ rmdir new_directory

• mv Command:

It is helpful to rename files or directories. mv command also moves a file or a directory to another location in the directory structure. Its syntax is $ mv file1 file2

Example: $ mv add sum

• pr -x Command:

It divides the file into x columns. Syntax is $ pr -x filename.

Example: $ pr -5 add

• pr -h Command:

It is useful to assign a header to the file. Syntax is $ pr -h filename

Example: $ pr -h sum

• pr -n Command:

This command denotes the file with the line numbers. Its syntax is $ pr -n file

Example: $ pr -n sum

• lp -nc , lpr c Command:

It prints the c number of copies of a file. lp stands for a line printer. Its syntax is $ lpr c filename

Example: $ lpr 5 sum

• lp -d lp -P Command:

It specifies the name of the printer. The syntax is $ lp -P

• apt-get Command:

It is a powerful and free front end package manager for Debian/Ubuntu systems. It is used to install new software packages, remove available software packages, upgrade existing software packages, and upgrade the entire operating system. Its syntax is $ apt-get package

Example: $ sudo apt-get update

• mail -s ‘subject’ -c ‘cc-address’ -b ‘bcc-address’ ‘to-address’ Command:

It is a linux command used to send mail. Syntax is $ mail -s ‘subject’ -c ‘cc-address’ -b ‘bcc-address’ ‘to-address’

Example: $ mail -s ‘regarding_job’ -c ‘[email protected]’ -b ‘[email protected]’ ‘[email protected]’

• mail -s “Subject” to-address < Filename Command:

It is used to send an email with an attachment. Its syntax is $ mail -s “Subject” to-address < Filename

Example: $ mail -s “Addition of Numbers” [email protected] < Addition

File Permission Commands

• ls-l Command:

Use this command to show file type and access permission of any particular file. Syntax is $ ls-l filename

Example: $ ls-l sum

• r Command:

It is used to give read permission to a file. The syntax is $ r filename.

Example: $ r sum

• w Command:

It gives write permission to the file. The syntax is $ w filename

Example: $ w sum

• x Command:

It is useful to provide execute permission to the file. Its syntax is $ x filename

Example: $ x sum

• -= Command:

This command is used when you want to give no permission to a file. Syntax is $ -= filename

Example: $ -= file1

• Chown user Command:

It is helpful to change the ownership of a file/directory. The syntax is $ chown user filename

Example: $ chown user file1

• Chown user:group filename Command:

It changes the user and group for a file or directory. Syntax is $ chown user:group filename

Example: $ chown user:group sum

Environment Variables Command

• echo $VARIABLE Command:

It displays the value of a variable or prints a text of the line. Its syntax is echo [option] [string]

Example: $ echo “Print this line” or $ echo $VARIABLE var1

• env Command:

It lists all environment variables. The syntax is $ env

• VARIABLE_NAME= variable_value Command:

It creates a new variable and assigns it a value. Syntax is $ VARIABLE_NAME= variable_value

Example: $ My_Variable= 10

• Unset Command:

It removes a variable. Syntax is $ Unset VARIABLE_NAME

Example: $ Unset My_Variable

• export Variable=value Command:

It is helpful to set the value of an environment variable. Syntax is $ export Variable=value

Example: $ export Variable1=90

User Management Commands of Linux

• sudo adduser username Command:

It is used to create a username. The syntax is $ sudo adduser username

Example: $ sudo dduser user1

• sudo passwd -l ‘username’ Command:

It is helpful to change the user password. Syntax is $ sudo passwd -l ‘username’

Example: $ sudo passwd -l ‘user1’

• sudo userdel -r ‘username’ Command:

This command is used to add and delete users on Linux. Syntax is $ sudo userdel -r ‘username’

Example: $ sudo userdel -r ‘user1’

• finger Command:

It is a user information lookup command which provides details of all users logged in. The Syntax $ finger

• finger username Command:

It gives the login details of that particular user. Syntax $ finger username

Example: $ finger user1

Networking Commands

• SSH username@ip-address or hostname Command:

You can log in to a remote Linux machine using SSH. The syntax is $ SSH username@ip-address or hostname

Example: $ SSH user1@https:11//1001

• Ping hostname=”” or =”” Command:

It is used for analyzing the network and host connections. Syntax is $ Ping hostname=”” or =””

Example: $ Ping hostname=”host1″

• dir Command:

It displays all files in the current directory of a remote computer. The syntax is $ dir

• cd “dirname” Command:

It changes the current directory to “dirname” on a remote computer. Syntax is $ cd “dirname”

Example: $ cd “E”

• put file Command:

It is helpful to upload the file from local to the remote computer. The syntax is $ put file

Example: $ put sum

• get file Command:

It is used to download the file from remote to the local computer. The syntax is $ get file

Example: $ get add

• quit Command:

It is used to logout from that network. The syntax is $ quit

Process Commands

• bg Command:

You can send a process to the background with this command. The syntax is $ bg processname

Example: $ bg process1

• fg Command:

To run a stopped process in the foreground. The syntax is $ fg processname.

Example: $ fg process1

• top Command:

It gives the details of all active processes in the directory. The syntax is $ top

• ps Command:

It produces the status of processes running for a user. The syntax is $ ps username

Example: $ ps user1

• ps PID Command:

This command gives the status of a particular process. The syntax is $ ps PID processname

Example: $ ps PID process1

• pidof Command:

It gives the process id of a process. The syntax is $ pidof processname.

Example: $ pidof process1

• kill PID Command:

It kills a process. The syntax is $ kill PID processname

Example: $ kill PID process1

• nice Command:

It is used to start a process with the given priority. The syntax is $ nice processname.

Example: $ nice process

• renice Command:

It is used to change the priority of an already running process. The syntax is $ renice processname

Example: $ renice process2

• df Command:

It provides free hard disk space on your system. The syntax is $ df

• free Command:

It gives free RAM space on your system. The syntax is $ free

VI Editing Commands

• i Command:

It inserts at the cursor i.e goes to insert mode. The syntax is $ i

• a Command:

It is used to write after the cursor in insert mode. The syntax is $ a

• A Command:

This command is used to write at the end of the line in insert mode. The syntax is $ A

• ESC Command:

It is helpful to terminate insert mode. The syntax is $ ESC.

• u Command:

It undoes the last change. The syntax is $ u.

• U Command:

It undoes all changes to the entire line. The syntax is $ U

• o Command:

It opens a new line in insert mode. The syntax is $ o

• dd Command:

It deletes that particular line. The syntax is $ dd line number

Example: $ dd 25

• 3dd Command:

This command deletes 3 lines. The syntax is $ 3dd line number

Example: $ 3dd 25

• D Command:

It deletes the contents of a line after the cursor. The syntax is $ D

• C Command:

It is used to delete the contents of a line after the cursor and insert new text. Press the ESC key to end the insertion. Syntax is $ C

• dw Command:

Delete a word using this command. The syntax is $ dw

• 4dw Command:

It is used to delete 4 words. The syntax is $ 4dw

• cw Command:

It is used to change a word. Syntax is $ cw

• x Command:

It deletes the character at the cursor. Syntax is $ x

• r Command:

Replace the character. The syntax is $ r

• R Command:

It overwrites characters from cursor onward. The syntax is $ R

• s Command:

Substitute one character under the cursor and continue to insert. The syntax is $ s

• S Command:

Substitutes the entire line and starts to insert at the beginning of the line. The syntax is $ S

• ~ Command:

It is used to change the case of the individual character. Syntax is $ ~

Other Linux Commands

• adduser/addgroup Command:

adduser adds a user and addgroup adds groups to the system. The syntax is $ adduser username

Example: $ sudo adduser tech

• agetty Command:

agetty is a program that manages physical or virtual terminals and is invoked by init. It is the substitute for Linux getty.

Example: $ agetty -L 9600 ttyS1 vt100

• alias Command:

It is a useful shell built-in command for creating shortcuts to a Linux command on a system.

Example: $ alias home’cd /home/drive/file1′

• apropos Command:

This is used to search and display a short man page description of a program/ command. The syntax is $ apropos commandname

Example: $ apropos rm

• aptitude Command:

It is a powerful text-based interface to the Debian Linux/GNU package management system. The syntax is $ aptitude package

Example: $ sudo aptitude update

• arch Command:

This command is used to display the machine architecture or hardware name. The syntax is $ arch

• arp Command:

ARP stands for Address Resolution Protocol that maps IP network addresses of a network neighbor with the hardware (MAC) addresses in an IPv4 network.

Example: $ sudo arp-scan –interface=enp2s0 –localnet

• at Command:

It is used to schedule tasks to run in the forthcoming time. Syntax is $ at

Example: $ sudo echo “shutdown -h now” | at -m 15:20

• atq Command:

This command is used to view jobs in at command queue. Syntax is $ atq

• atrm Command:

It is helpful to delete/remove jobs from the queue. $ atrm 2

• awk Command:

Awk is a programming language created for text processing and used as a data extraction and reporting tool.

Example: $ awk ‘//{print}’/etc/hosts

• batch Command:

It is similar to at command which is useful to schedule tasks to run in a future time. Syntax is $ batch

• basename Command:

It helps to print the name of a file stripping of directories in absolute path. Syntax is $ basename filename

Example: $ basename samplefile

• bzip2 Command:

It is useful to compress or decompress the files. Syntax is $ bzip2 filename

Example: $ bzip2 -z filename #Compress

$ bzip2 -d filename.bz2 #Decompress

• cal Command:

This command is used to print a calendar on the standard output. Syntax is $ cal

• chgrp Command:

It is used to change the group ownership of a file. Syntax is $ chgrp new_group_name filename

Example: $ chgrp Product Multiplication.txt

• chmod Command:

It is used to change/ update file access permissions. Syntax is $ chmod permission filename

Example: $ chmod +x product.txt

• cksum Command:

This command is used to provide the checksum and byte count of the given input file. Syntax is $ cksum filename

Example: $ cksum product.txt

• cmp Command:

It compares byte by byte comparison of two files. Syntax is $ cmp file1 file2

Example: $ cmp sum add

• comm Command:

It is used to compare two sorted files line by line. Syntax is $ comm file1 file2

Example: $ comm product multiplication

• cp Command:

It copies files and directories from one location to another. Syntax is $ cp location1 location2

Example: $ cp /home/arithmetic/add /home/arithmetic/product/

• date Command:

It displays/ sets the system date and time. Syntax is $ date

Example: $ date –set=”20 Oct 2020 10:35:05″

• diff Command:

The double advantage of this command is used to compare two files line by line and used to find the difference between two directories. Syntax is $ diff file1 file2

Example: $ diff sum add

• dmidecode Command:

It retrieves the hardware information of any linux system. Syntax is $ dmidecode

Example: $ sudo dmidecode –type system

• du Command:

It shows the disk space usage of files present in the directory as well as its subdirectories. The syntax is $ du directory

Example: $ du /home/arithmetic

• eject Command:

eject command is used to eject removable media such as CD/DVD/ROM/floppy disk from the system. The syntax is $ eject disklocation

Example: $ eject /dev/cdrom

• exit Command:

It is used to exit a shell. The syntax is $ exit

• expr Command:

It is used to calculate an expression. The syntax is $ expr expression

Example: $ expr 15 * 5

• factor Command:

It is used to display the prime factors of a number. The syntax is $ factor number

Example: $ factor 18

• find Command:

It searches for files in the directory and its subdirectories. The syntax is $ find directory filename

Example: $ find /home/add/ -name product.txt

• grep Command:

It searches for a specified pattern in the file and displays the output as lines containing that pattern. The syntax is $ grep

Example: $ grep ‘linuxcent’ domain-list.txt

• groups Command:

Shows all names of groups of a user. The syntax is $ groups

• gzip Command:

It helps to compress a file and replaces it with one having a .gz extension. The syntax is gzip filename

Example: $ gzip passwds.txt

• gunzip Command:

It expands or restores files compressed with the gzip command. The syntax is $ gunzip gzfilename

Example: $ gunzip sum.gz

• head Command:

It is helpful to display the first 10 lines of the specified file or stdin to the screen. The syntax is $ head

• hostname Command:

This command is useful to print or set the system hostname. The syntax is $ hostname

Example: $ hostname New_hostname

• id Command:

It shows user & group information for the current user or specified user. The syntax is $ id username

Example: $ id linuxcent

• ifconfig Command:

It is used to configure Linux system network interfaces. The syntax is $ ifconfig

• ionice Command:

This command is used to set or view process I/O scheduling class and priority of the specified process. The syntax is $ ionice process

Example: $ ionice -c 3 rm /var/logs/syslog

• iostat Command:

iostat command is helpful to show the CPU and i/o statistics for devices and partitions. The syntax is $ iostat

• ip Command:

It is used to display or manage devices, routing, policy routing, and tunnels. The syntax is $ ip addr

• iw Command:

This is used to manage wireless devices and their configuration. The syntax is $ iw

Example: $ iw list

• killall Command:

It kills a process with the help of its name. The syntax is $ killall processname

Example: $ killall process1

• kmod Command:

It is useful to manage Linux kernel modules. To list all currently loaded modules, type. Syntax is $ kmod

Example: $ kmod list

• last Command:

It displays a list of last logged in users. The syntax is $ last

• ln Command:

This is used to create a soft link between files using -s flag. Syntax is $ ln -s file1 file2

Example: $ ln -s product multiplication

• locate Command:

It is used to find a file with its name. The syntax is $ locate filename

Example: $ locate -b ‘add.txt’

• lshw Command:

It gives detailed information on the hardware configuration of the machine. The syntax is $ lshw

• lscpu Command:

This Linux command displays the system’s CPU architecture information. The syntax is $ lscpu

• lsof Command:

It displays information related to files opened by processes. The syntax is $ lsof processname

Example: $ lsof -u add

• lsusb Command:

It shows information: about USB buses in the system and devices connected to them. The syntax is $ lsusb

• md5sum Command:

This command is used to compute and print the MD5 message digest of the file.

• more Command:

It enables to view through relatively lengthy text files one screenful at a time. The syntax is $ more filename

Example: $ more add

• nano Command:

You can open a file using this nano command. The syntax is $ nano filename

Example: $ nano sum

• netstat Command:

It displays useful information such as routing tables, network connections, and others about Linux networking subsystems. Syntax is $ netstat

Example: $ netstat -a | more

• nproc Command:

It shows the number of processing units present to the current process. The syntax is $ nproc

• passwd Command:

This command is used to create/update passwords for user accounts. The syntax is $ passwd username

Example: $ passwd user1

• pstree Command:

It displays running processes as a tree that is rooted at either PID or init if PID is omitted. The syntax is $ pstree

• reboot Command:

This command is used to power-off, halt, or reboot a system. The syntax is $ reboot

• scp Command:

It enables you to securely copy files between hosts on a network. Syntax is $ scp

Example: $ scp ~/names.txt [email protected]:/root/names.txt

• shutdown Command:

It schedules a time for the system to be powered down. Its syntax is $ shutdown

Example: $ shutdown –poweroff

• sleep Command:

This command is used to pause or delay for a specific amount of time. The syntax is $ sleep

Example: $ check.sh; sleep 5; sudo apt update

• sort Command:

This is used to sort lines of text in the specified files from stdin. The syntax is $ sort

Example: $ sort add.txt

• split Command:

It is used to split a large file into smaller pieces. The syntax is $ split filename

Example: $ split add

• stat Command:

It is helpful to know the file system status. The syntax is $ state filename

Example: $ stat -f add.txt

• su Command:

It is used to switch to another user ID or become root during a login session. The syntax is $ su

• sum Command:

This command shows the checksum and blocks counts for all files on the command line. The syntax is $ sum output filename

Example: $ sum output add.txt

• tac Command:

It concentrates and displays files in reverse. It prints each file to the standard output, shows the last line first. The syntax is $ tac filename

Example: $ tac sum.txt

• tail Command:

It displays the last 10 lines of each file. The syntax is $ tail filename

Example: $ tail sum.txt

• talk Command:

talk is used to talk to another network user/ system. Use a login name to talk to the user on the same machine and use ‘use@host’ to talk to a user on another machine. The syntax is $ talk

Example: $ talk person [ttyname] or $ talk ‘user@host’ [ttyname]

• tee Command:

This is used to read from standard input & prints to standard output and files.

Example: $ echo “Testing how tee command works” | tee file1

• time Command:

This command runs programs and summarizes system resource usage. The syntax is $ time

• touch Command:

It changes file timestamps and it is used to create a file. The syntax is $ touch filename

• uname Command:

It displays system information such as operating system, network node hostname kernel name, version, and release, etc. Syntax is $ uname

• uniq Command:

It displays or omits repeated lines from input. The syntax is $ uniq

• uptime Command:

It shows how long the system has been running, the number of logged on users, and system load averages. The syntax is $ uptime

• wall Command:

This command is used to send/display a message to all users on the system. The syntax is $ wall “message”

Example: $ wall “This is Linux operating system”

• wc Command:

This command displays the word, newline, and byte counts for each file. The syntax is $ wc filename

Example: $ wc add.txt

• whatis Command:

It searches & shows a short or one-line manual page description of the provided command name. The syntax is $ whatis wget

• who Command:

It shows details about users who are currently logged in. The syntax is $ who

• which Command:

This command is used to get the absolute path of the file which would be executed in the current environment. The syntax is $ which who

• whereis Command:

It helps to locate binary, source and manual files for commands. The syntax is $ whereis cat

• yes Command:

This command is used to display a string repeatedly until when terminated or killed. The syntax is 4 yes

Example: $ yes “This is LinuxCent – Linux HowTos”

• zcmp/zdiff Command:

zcmp and zdiff minimal utilities used to compare compressed files. Syntax is $ zcmp filesnames, $ zdiff filesnames

Example: $ zcmp domain-list.txt.zip basic_passwords.txt.zip

$ zdiff domain-list.txt.zip basic_passwords.txt.zip

• zip Command:

It is simple & easy to use utility used to package & compress files. Syntax is $ zip packagename

Example: $ zip inarchive.zip foo.c bar.c –out outarchive.zip

We have mentioned all the Linux commands in the Linux Commands Cheatsheet. Make use of these countless commands that you might feel helpful.

What are 5 Linux commands?

Linux File commands

• touch Command. The touch command is used to create empty files. …
• cat Command. The cat command is a multi-purpose utility in the Linux system. …
• rm Command. The rm command is used to remove a file.
• cp Command. The cp command is used to copy a file or directory.
• mv Command. …
• rename Command.

How do I see all commands in Linux?

In Linux, there is a very useful command to show you all of the last commands that have been recently used. The command is simply called history, but can also be accessed by looking at your . bash_history in your home folder. By default, the history command will show you the last five hundred commands you have entered.

What is Linux cheat sheet?
Basic Linux commands

How many commands are in Linux?

There are well over 100 Unix commands shared by the Linux kernel and other Unix-like operating systems.

What does F do in Linux?

Many Linux commands have an -f option, which stands for, you guessed it, force! Sometimes when you execute a command, it fails or prompts you for additional input. This may be an effort to protect the files you are trying to change or inform the user that a device is busy or a file already exists.

How do I get a list of commands?

You can open the Command Prompt by pressing ⊞ Win + R to open the Run box and typing cmd. Windows 8 users can also press ⊞ Win + X and select Command Prompt from the menu. Retrieve the list of commands.

How do you list all commands in Terminal?

Just tap the Tab key twice ( Tab Tab ). You’ll be prompted if you want to see all possible commands. Tap y and you’ll be presented with a list. You can do that same thing for individual commands to see all options for that specific command.

How do you write commands in Linux?

Linux operating system allows users to create commands and execute them over the command line. To create a command in Linux, the first step is to create a bash script for the command. The second step is to make the command executable. Here, bashrc means run the Bash file.

What does Linux dd command do?

dd is a command-line utility for Unix and Unix-like operating systems, the primary purpose of which is to convert and copy files. … As a result, dd can be used for tasks such as backing up the boot sector of a hard drive, and obtaining a fixed amount of random data.

What is Yum in Linux?

YUM is the primary package management tool for installing, updating, removing, and managing software packages in Red Hat Enterprise Linux. YUM performs dependency resolution when installing, updating, and removing software packages. YUM can manage packages from installed repositories in the system or from

What is Sudo in Linux?

Sudo stands for either “substitute user do” or “super user do” and it allows you to elevate your current user account to have root privileges temporarily. This is different from “su” which is not temporary.

How use Linux command line?

On many systems, you can open a command window by pressing the Ctrl+Alt+t keys at the same time. You will also find yourself on the command line if you log into a Linux system using a tool like PuTTY. Once you get your command line window, you’ll find yourself sitting at a prompt.

What is Ubuntu command?

The latest LTS release is 20.04; it will be available till 2025. Ubuntu supports both Command Line Interface (CLI) and Graphical User Interface (GUI) to perform various tasks on the OS. CLI is the basic way to interact with systems hardware (processor/memory); you can perform all the tasks that GUI can perform.

Where is Linux command?

The whereis command in Linux is used to locate the binary, source, and manual page files for a command. This command searches for files in a restricted set of locations (binary file directories, man page directories, and library directories).