Linux Commands

ls command

• ls : to list directories and files
• ls -a : to list all files and directories alongwith hidden ones
• ls -r : lists files and directories in reverse alphabetical order.
• ls -l : to give detailed info of directories/files like when created and by whom, date modified, size, permissions and ownerships
• ls -al : to list all hidden files with details.
• ls -lh : to list file with details of file size in - KB (kilobytes).
• ls -lR : to list all the directories and their - sub-directories with details.
• ls -lR dirName : to list the details of - sub-directories of the specified dirName.
• ls -F : to identify files and directories - seperately. Directories will be listed with a "/" - symbol at the end of directory name
• ls -i : displays the inode [index number] of each - file
• ls --sort=t or ls -t : displays the list of files / directory sorted by time. Similarly sort=v/s/e for sort by version/size/extension

Directory

Directory Creation

• mkdir [FOLDER-NAME] : to create a folder/ directory
• mkdir folder1 folder2 folder3 : to create multiple folders/ directory at once
• mkdir file{1..9} : this will create 10 folders with name 'file 1', 'file 2', ..., 'file 10'
• mkdir -v folders{1..7} : this will create folders & will skip the ones which are already created before with the same name.
• mkdir -p [PATH] : will create 'cmds' folder in the given path but if the path doesn't exits then it will be created.

Remove directoy

• rmdir [DIR-NAME] : to remove the file/ folder/ directory.
• rmdir myFolder* : removes all folders that begins with name 'myFolder'
• rmdir * : removes all the folder in the present directory.
• rmdir myFolder{1..7} : removes the folders from 'myFolder 1' to 'myFolder 7' NOTE: rmdir cannot delete diectories having files / folders inside.
• rm -R [DIR-NAME] : to delete the directory with the files inside.
• rm -r [DIR-NAME]: to delete all the files and NON-EMPTY directories and also the child folders content.

Change Directory

• cd : to change directory to home/user directory
• cd ~ : to go to home/user directory
• cd / : to go to root directory
• cd [DIR-NAME] : to change directory or go to that directory
• cd .. : to go to the parent directory

File management

Create or manipulate file

• touch [FILE-NAME] : to create a file
• touch -m [FILE-NAME] : change modification time of the file
• touch -a [FILE-NAME] : change the access time of the file
• touch test{1..5}.txt : create 5 files with name test1.txt, test2.txt, ..., test5.txt
• cat > [FILE-NAME] : to rewrite a file. If the filename not present then new file with given name will be created
• cat >> [FILE-NAME] : to append new contents to the file [ NOTE: for cat > or >> ... commands, inorder to exit writing mode of the file press CTRL+D.]

Delete files

• rm [FILE-NAME] : to remove dir/ file/ folder.
• rm * : removes all the files in the current directory.
• rm *.txt : removes all the files in the current directory that has .txt extension.
• rm -i [FILENAME] : to make command prompt the user with each filename while deleting

Move and Copy

• mv [SOURCE] [DESTINATION] : to move the file into the given destination or path.
• cp [FILE-1] [FILE-2] : copies the file1 contents to file2.
• cp [FILE-NAME] : will copy the file in the directory.

Show file contents

• cat [FILE-NAME] : to show the contents of file in the terminals.

Change filename

• mk [PRESENT-FILENAME] [NEW-FILENAME] : this changes the file or folder name.

Octal form

• od [FILENAME] : to display a file contents in octal form

file command

• used to display file type

  file video.mp4
  

  Output:

  video.mp4: ISO Media, MP4 Base Media v1 [ISO 14496-12:2003]
  

Locate a file

• find [FILENAME] : search for files in a directory hierarchy

File Comparison

cmp command

• Compare two files byte by byte

  cmp file1.txt file2.txt
  

  Output:

  file1.txt file2.txt differ: byte 8, line 1
  

diff command

• used to compare files line by line

  diff [FILE-1] [FILE-2]
  

Examples:

• to show the difference of two files side by side

  diff -y file1.txt file2.txt
  

  • -y : side-by-side output in two columns

comm command

• Used to compare two sorted files

  Contents of file1.txt :

  ANGULAR
  DJANGO
  ELECTRON
  FLASK
  NODEJS
  REACT
  YARN
  

  Contents of file2.txt :

  ANGULAR JS
  FASTAPI
  FLASK
  NEXT JS
  NODEJS
  REACTJS
  YARN
  

  Command line input:

  comm --total file1.txt file2.txt
  

  Output:

  ANGULAR
  	    ANGULAR JS
  DJANGO
  ELECTRON
  	    FASTAPI
  		        FLASK
  	    NEXT JS
  		        NODEJS
  REACT
  	    REACTJS
  		        YARN
  4	4	3	total
  

  • unmatched file of first file is displayed in 1st column
  • unmatched file of first file is displayed in 2nd column
  • matched lines in 3rd column
  • --total : counts the number of lines that are matched and unmatched for both the files.

File Permissions

chmod (change mode)

• use to change permissions of a file or directory of all types of users

• Control of a file:

  • d : directrory
  • - : no permission given [NOTE: the leftmost - implies its a file]
  • Permissions
    • r : read(4)
    • w : write (2)
    • x : executable (1)

  Example:

  chmod +x program.sh
  

  The above command grants executable permissions to the program.sh file for all the users

  -rwxrwxr-x  1 deroyace deroyace    127 May 23 15:3 counter.sh
  drwxr-xr-x  3 deroyace deroyace   4096 Mar 29 19:2 Desktop
  

  • rwx is written 3 times consecutively. This means,
    • first set of rwx implies USER / OWNER permission
    • second set implies GROUP permissions same as owner.
    • third set implies OTHERs outside the group.
    • left most single symbol d indicates it is a directory. It can be l or - also.
      • l means its a shortcut link of a file or a directory.
      • - means it is a file.

• Numerical Short hand or Octal Mode

  • Another way to use chmod is to provide the permissions you wish to give to the owner, group, and others as a three-digit number which is basically octets that are formed by combinations of 4,2 and 1.

  • The leftmost digit represents the permissions for the owner.

  • The middle digit represents the permissions for the group members.

  • The rightmost digit represents the permissions for the others.

    Value   Symbols    Meanings/ Permissons
      0       ---       No permission
      1       --x       Execute
      2       -w-       Write
      3       -wx       Write and execute
      4       r--       Read
      5       r-x       Read and execute
      6       rw-       Read and write
      7       rwx       Read, write, and execute
    

    Examples:

    • Give read, write, execution permissions to all types of users:

      chmod 777 program.sh
      

    • Give read, write, execution permissions only to User and Group:

      chmod 770 program.sh
      

    • Give read, write, execution permissions to User and read nad execution permission to Group and only execution permission to other users:

      chmod 751 program.sh
      

  • Default permissions for:

    • file : 664 (-rw-rw-r--)
    • folder : 775 (drwxrwxr-x)

• Symbolic Mode

   Symbol     Meaning
  -------------------
     a         all users
     u         user
     g         group
     o         others
  

  Examples:

  • Give read, write, execute permission to user and execute permission to group and other

    chmod u+rwx,go+x program.sh
    

  • Give read permission to all, write permission to user and group, execute persmission to group only:

    chmod u+rw,g+rx,o+r program.sh
    

  • Give read, write, execute permission to user and execute permission to group and other:

    chmod u+rwx,go+x program.sh
    

  • Make all files and sub-directories in the directory TEST executable by all users

    chmod -R a+x TEST
    

  • Remove executable permission from group and other of a file

    chmod go-x file.txt
    

chgrp (change group)

• chgrp [GROUP-NAME] [FILE/FOLDER NAME] : to assign a file/folder to a specific group

chown (change owner)

• sudo chown [USER-NAME] [FILE/FOLDER-NAME] : to change the user or ownership of a file/folder:

File Compression

tar command

• it is used to compress and archive files
• TAR short for Tape Archive

Examples:

• To create a tar and includes the files specified in the command:

  tar cf file.tar [FILE-NAMES]
  

  • c : create new archive
  • f : to specify name of the archive files
  • [FILE-NAMES] : represent files that are to be included in the tar file

• Extract From tar Archive

  tar xf file.tar
  

  • x : extract files from an archive

• Creating an uncompressed tar Archive:

  tar cvf file.tar *.sh
  

  • This command creates a tar file called file.tar which is the Archive of all .sh files in the current directory.
  • v : verbosely list files processed

• Extracting from uncompressed tar archive:

  tar xvf file.tar
  

• Create a tar.gz Compressed Archive:

  tar czf files.tar.gz files
  

• Extract files from tar.gz

  tar xzf files.tar.gz
  

Wild cards

• *, ? are wilcards

• Use of wild cards:

  • ls *.txt : list all files that ends with .txt extension

    • * implies any number of characters

  • To list all files that starts with "file" and succeeds by any one character and then ".txt": ls file?.txt

  • ls file???.txt

    • ? two characters
    • ??? means any 3 character

sort command

• to sort lines of text files lexicographically

Examples:

• sort the lines of file in alphabetical order:

  sort  [FILENAME]
  

• sort the lines of file in reverse order:

  sort -r [FILENAME]
  

• output the sorted file into a new file:

  sort  [FILENAME] > [NEW-FILE]
  

• output the sorted lines of a file into a new file without duplicates:

  sort [FILENAME] > uniq > [NEW-FILE]
  

ln command

• used to make links between files

• ln [FILE-NAME] [HARD-LINK]: Create a hard link for a file (same inode)

• ln -s [FILE-NAME] [SOFT-LINK]: Create a soft link for a file

• ln -s .. [SOFT-LINK]: Create a soft link for the parent directory you are currently located in

grep command

• prints each line of a file that matches a pattern

Examples:

• list all directories present in the current folder

  ls -l | grep ^d
  

  • ^d : matches those lines that starts with letter 'd'

  Output:

• Show the line numbers that matches the pattern "hello", ignoring case

  grep -i -n "hello" file.txt
  

  • -n : displays line number
  • -i : ignores case

• Ignore those lines that matches the pattern "hello"

  grep -v "hello" [FILENAME]
  

• To highlight words in a file or command output that ends with letter 'A':

  grep "\b\w*A\b" [FILENAME]
  

  • -b : boundary
  • \w* : any number of characters

• Specifically display and highlight only those words that starts with letter 'A' or 'a':

  grep -o -i "\b\A\w*\b" [FILENAME]
  

  • -o : outputs only matching words
  • -i : ignores case [ NOTE: it works only when capital letter is used in the command to find the required search. ]

CUT

• used to extract characters or remove sections from each lines of files

Examples:

• To extract first three characters of every line:

  cut -c -3 [FILENAME]
  

• To extract characters starting from 2nd character of every line:

  cut -c 2- [FILENAME]
  

• To extract last three characters of every line:

  cat [FILENAME] | rev | cut -c -3 | rev
  

• To display selected columns sorted by ID:

  cut -d $'\t' -f1-4 movies.txt | sort -k1 -n
  

  • $'\t' : tab space delimiter [taking columns seperated by TAB space]
  • -d : delimiter
  • -n : numeric value sorted
  • -f1-4 : columns 1 to 4
  • -k1 : sort by first column
  • -k2 : sort by second column

PASTE

• paste [FILENAME-1] [FILENAME-2] : concatenates two files. by default the delimiter is TAB
• To explicity specify a delimiter/ concat file contents using delimiter:

  paste -d '-' [FILENAME-1] [FILENAME-2]
  

User and Group handling

Switch user

• su root : to go to the root account. '$' will change to '#'; su -> switch user
• sudo su : switching user

User Password

• passwd : to change your login or root account password.

• passwd [Account Name] : to change password of that particular account.

• id [USER-NAME] : shows user id; root account id is 0.

Create New User / Group

• sudo adddgroup [GROUP-NAME] : to create new User Group
• sudo adduser [USERNAME] : to create a new user account.
• sudo usermod -aG sudo [USERNAME] : to make the user as a root user.

Remove User / Group

• sudo groupdel {GROUP-NAME} : to remove a group:

Process management

• top: list all processes and shows the cpu, memory usage and running background apps.
• ps aux : lists all processes that are currently running in the device.
  • a : --all Display information about other users' processes as well as your own.
  • u : Display the processes belonging to the specified usernames.
  • x : When displaying processes matched by other options, include processes which do not have a controlling terminal.
• kill [PID] : kills or disables a process
• kill -9 [PID] : stop a process

OS, CPU and Kernel information

• uname -a : show kernel information

• xdpyinfo | grep 'dimensions:' : to check screen resolution Result from above cmd: dimensions: 1366x768 pixels (361x203 millimeters)

• To check distro release version:

  • lsb_release -a : provides certain LSB (Linux Standard Base) and distribution-specific information.
  • cat /etc/os-release

• echo $XDG_CURRENT_DESKTOP : to check Desktop Environment

• cat /proc/cpuinfo : cpu information

Memory information

• df : shows the disk space usage
• du : shows directory space usage
• free : shows memory and swap usage
• cat /proc/meminfo : memory information

Path Locate

• pwd : shows the path of current working directory
• locate [SEARCH-NAME] : to search files by name
• whereis [APP/COMMAND] : to locate binary file, manual page files of applications or commands
• which [APP/COMMAND]: to locate a command or an application

Other useful commands

• man [COMMAND] : shows the mannual page of the command
• history : list all the cmds used (last 500 cmds)
• lsusb : shows the USB buses and devices connected
• whatis [COMMAND] : to give brief description or use of that command
• whoami : checks whether you are root user/ whats the user name you are logged in as
• who : display information about users who are currently logged in
• w : show who is logged on and what they are doing
• tty : print the file name of the terminal connected to standard input
• !! : executes the last command
• exit : log out current session

Shortcuts

• CTRL + ALT + T : to open terminal [NOTE: this may vary in distros, may not work for some]
• CTRL + SHIFT + W or CTRL + D : to close terminal
• CTRL + L : to clear the terminal
• CTRL + C : to terminate the program
• CTRL + D : TO log out of current session, similar to exit
• CTRL + Z : to pause/suspend the program
• CTRL + A : to go to start of the line/ command
• CTRL + E : to go to end of the line/ command
• CTRL + U : to clear the command
• CTRL + R : type to bring up a recent command

---