Day 4 . Linux Commands

Basic Linux commands

date - Date command is used to display the system’s date and time. In the output screen, you can see your system’s date and time.

date

cal - command is a calendar command in Linux which is used to see the calendar of a specific month or a whole year. In the terminal, type cal and press Enter.

cal

clear - This is a standard Linux operating system command that is used to clear the terminal screen.

clear

bc- Basic Calculator is a command line utility that offers everything you expect from a simple scientific calculator. To use this calculate, in the terminal, just type bc and press Enter.

bc

quit - Do you want to get out of calculator mode? Just type quit command and press Enter, which will take to you to the terminal.

quit

pwd - Do you know, you can see the working directory path pwd command stands for Print Working Directory.

pwd

cd /directory/folder/path – change between different directories.

cd /directory/folder/path

cd.. – moves one directory up

cd..

File and Directories commands

ls [/directory/folder/path] - This ls command is used to check the contents of the directory you are in.

ls [/directory/folder/path]

mkdir [directory] – create directory, specify directory name.

mkdir [directory]

create file

nano [file] - using nano editor

nano [file]

touch [file] – create file.

touch [file]

echo "Text" > [file] - The echo command will duplicate whatever you specify in the command, and put the copy into a file.

echo "Text" > [file]

vi [file] – using vi editor.

vi [file]

vim [file] – Its more user friendly which stands for vi editor, modified.

vim [file]

cat [file] is a command used to view the contents of a file. You can see it in the output of a command. Let’s view the content of one more file.

cat [file]

less [file]- you can see the contents on one page at a time. You can move by pressing the up and down keys. Type q to exit.

less [file]

head [option] [file]– displays some top lines of file. We can use option(–) to display top n lines of file. We can modify command with options as below.

head [option] [file]

• -n – changes the number of lines printed. For example, head -n 5 shows the first five lines.

• -c – prints the file’s first customized number of bytes.

• -q – disables headers specifying the file name.

head [option] [file]

tail [option] [file]– displays bottom lines of file. We can use option(-) to display bottom n lines of file. We can modify command with options as below.

• -n – changes the number of lines printed. For example, head -n 5 shows the first five lines.

tail [option] [file]

nl [option] [file] – we can display line numbers before each line. We can modify command using below options.

• -b: This parameter is used to specify the numbering style

• -n: This parameter is used to format the line numbers.

nl [option] [file]

cp [source] [destination] – copies file from source to destination.

cp [source] [destination]

mv [source] [destination] – moves file from source to destination.

mv [soucre] [destination]

rm [file] – delete a file.

rm [file]

rmdir [directoryname] – removes directory. Use option(-r) to delete files and directories recursively.

rmdir [directory]

User and Groups permissions command

ls –l – This command will display details of file with permissions.

ls -l

sudo useradd [option] [username] –p [PASSWORD] – useradd command is used to create user.

-m - makes users home directory, if does not exist.

-p - provide password foe user

sudo useradd [option] [username] =p [password]

sudo groupadd [groupname] – groupadd command is used to create group.

sudo groupadd [groupname]

sudo usermod [option] [groupname] [username] – usermod is used to add user to group.

sudo usermod [option] [groupname] [username]

sudo su [username] – su command is used to switch user.

uso su [username]

sudo su [username] – sudo command is used to allow to run command using security privileges of other user.

sudo su username

chmod [option] [permission] [filename] – modify user permissions. Different permissions used are.

• -r – read permission(4)

• -w – write permission(2)

• -o – execute permission(1)

chmod [option] [permission] [file]

chown [option] [username] [filename]- change user of file.

chown [option] [username] [file]

Installing and updating packages

apt install [packagename] – install packages

apt install [packagename]

apt update – update packages.

apt update

Other Linux commands

wc [file] – get number of lines and word count of file.

wc [file]

ls [filename]*– ls command to search all file name started with “file”.

ls [file]*

ls [characters in word] - This command returns all file name which contains character.

ls [characters in file]

alias [aliasname]=["command name"] – We can use alias for command.

alias [aliasname] =["command name"]

unalias command [aliasname] – remove alias for command.

unalias [command name] [aliasname]

hostname – returns hostname.

hostname

history – This command shows history of all used commands.

history

Searching for files

find . –name ["filename"] – returns directory of file.

find . -name ["filename"]

find . –type d(option -type) - names of all the directories and subdirectories under the current directory.

find . -type d

find . –perm 644(option –perm) – returns files with permissions.

find . -perm 644

Using pipes

pipe (|) – used to combine 2 or more commands

head [file] | wc -w

head [filename] | wc -w

Searching with grep

grep [option] ["any word in file"] [filename] – search text in file. We can modify command using below options.

• -n : returns line number

• -w: search whole word in file

grep [option] ["any word in file"] [file]

Working with .tar and .zip files

tar [option] [archive file] [file1] [file2] – archive files into tar file

• **-**c- crate archive

• -f – archive to file

• -a – kind of compression

• -x- extract files

• -C- target directory

tar [option] [archive file] [file1] [file2]

zip [option] [zip file] [file1] [file2] – used to compress files into zip file.

• -d - removes file from archive

• -u - updates file in archive

• -m - moves file into archive

• -r - recursively archive files

zip [option] [zip file] [file1] [file2]

unzip [zip file] [directory] – extract content of zip file into folder.

unzip [zip file] [directory]

gzip, gunzip, bzip2, unzip: Compress and decompress files.

Links

ln [option] [file] [folder] – this command is used to avoid having multiple copies of the same file in different places.

–s ensures that symbolic link is created.

ln [option] [file] [folder]

Environment variable

env – displays list of environment variables.

env

echo $[environment variable] – It is used to return value of environment variable

echo $[environment variable]

Input/Output redirects

[first command] > [output file]> - this command redirects output of command to file[option 2> - standard error redirection , &2 – standard output and error redirection.

[command] > [output file]

[command] < [file]< - this command redirects output from file.

[command] < [file]

Standard output to file

[command] | tee [option] [output file] –tee command is used to display output of command is as well as save in file.

-a Option : It basically do not overwrite the file but append to the given file.

[command] | tee [option] [output file]

Text processing command

cut [option] [character range] [file]cut scommand is used to select specific column of file.

• -f – selects a specific field.

• -b – cuts the line by a specified byte size.

• -c – sections the line using a specified character.

• -d – separates lines based on delimiters.

cut [option] [character range] [file]

awk [option] '{action}' [file] – used for text processing.

-f - Reads the awk program source from the file

-F fs Use fs for the input field separator

awk [option] '{action}' [file]

grep ["text to be searched"] [file] – search text in file.

grep ["text to be searched"] [file]

sort [option] [file]– sort data alphabetically(-n option for numbers). We can modify sort command using below options.

• -o – redirects the command outputs to another file.

• -r – reverses the sorting order to descending.

• -n – sorts the file numerically.

• -k – reorders data in a specific field.

sort [option] [file]

uniq [file] – omit repeated lines.

uniq [file]

wc [file] - returns no of lines, words and characters in each line of file(option –l –line, -w – word, -c – character)

wc [file]

Compare files

diff [file1] [file2] – get difference in both file.

diff [file1] [file2]

cmp [file1] [file2] – It returns at what line difference is.

cmp [file1] [file2]

Processes in linux

ps – displays process in current shell.

The ps command accepts several options, including:

• -T – displays all processes associated with the current shell session.

• -u username – lists processes associated with a specific user.

• -A – shows all the running processes.

ps

kill [signal] [process id] – terminate process with signals.

kill [signal] [process id]