Linux & Terminal Commands

A shell is a command-line interface which allows to perform certain tasks using command

Basic Commands

• cd → change directory
  • cd .. → goes back a single directory
• mkdir → make new folder
  • mkdir -p → makes directories and sub-directories too.
• touch → creates a new file
• ls/dir → lists all the files in the current directory
  • ls -a → displays all the hidden files
  • ls -l → shows more information like size, date about the files in working directory.
  • ls -R → show files, directories and sub-directories as well.
• xdg-open / open → opens the graphical interface of the present working directory.
• pwd → Print Working Directory
• cp → creates a copy of a file or a folder
  • cp -R → copies directories and also the sub-directories
• mv → moves files If names of two files are given, then the file gets renamed.
• rm → removes only files permanently.
  • rm -R → removes directories permanently.
  • rm -rf → force remove of files or directories.
• sudo → Super User Do gives system administrator privileges. sudo apt update && sudo apt upgrade is used to download and install updates.

File Commands

• echo → displays

• cat stands for concatenate, it is used to display the contents of a file

  • cat > creates a file.

• vi <file_name> allows editing the file in the console.

  

  • press i to enter insert mode and Esc to enter command mode.
    • I - Insert text at the beginning of the current line
    • A – Write at the end of the line (goes into insert mode)
    • b → Go to the beginning of the word
    • e → Go to the ending of the word
    • u – Undo last change
    • U – Undo all changes to the entire line
    • o – Open a new line (goes into insert mode)
    • dd – Delete line
    • 3dd – Delete 3 lines.
    • D – Delete contents of the line after the cursor
    • C – Delete the contents of a line after the cursor and insert new text.
    • dw – Delete word
    • 4dw – Delete 4 words
    • cw – Change word
    • x – Delete the character at the cursor
    • ~ – Change case of individual character
  • :wq → writes and quit the file in command mode
  • :q! → quit without saving the changes in command mode
  • :w → save and continue editing
  • yy → Yank (copy a line of text)

  An introduction to the vi editor (opens in a new tab)

• head → displays the first 10 lines of a file

  • head -n 1 → displays the first line of a file

• tail → displays the lasts 10 lines of a file

  • tail -n 1 → displays the last line of a file

• diff → compares files and displays lines which does not match

• tr → translate

• grep → searches Strings in files.

  • grep -w → searches Strings of a complete word in files.
  • grep -i → [ignore cases] searches non-case sensitive Strings in files.
  • grep -n → searches Strings in files and also displays the line no.
  • grep -win → search non-case sensitive Strings in words in files and also displays the line no.
  • grep -B 3 → also displays 3 lines before the searched Strings.
  • grep -r → searches Strings in files recursively.
  • grep -l → displays list of filenames only.
  • grep -c → display the no of times the search string is present in a file
  • grep -p → is used to search regular expressions

• sort → displays lines of file sorted alphabetically.

  • sort -r → displays lines of files sorted in reverse
  • sort -b → ignores blacks while sorting
  • sort -f → ignores cases while sorting
  • sort -n → sorts numerical value

• lsof → lists all the opened files

  • lsof -u driptanil → displays all the opened files by ‘driptanil’ user

• cut → remove sections from each line of files

  • cut -b → removes only bytes
  • cut -c → removes only characters

• locate "*.txt" → will display location of all the .txt files.

• find . → displays all the files and folder in the working directory.

  • find . -type d → displays all the folders in the working directory.
  • find . -type f → displays all the files in the working directory.
  • find -name → displays all files and folders with the name in working directory.
  • find -iname → displays all files and folders with the name [not case sensitive] in the working directory.
  • find -mmin -15 → displays all the files and folders modified less than 15 mins ago.
  • find -mmin +30 → displays all the files and folders modified more than 30 mins ago.
  • find -mtime -10 → displays all the files and folders modified less than 10 days ago.
  • find -maxdepth 1 → displays files and folders in working directory.
  • find -mindepth 2 → displays files and folders in the folders in working directory.
  • find -size +1k → displays files and folders more than 1 Kb size.
  • find -empty → displays files and folders which are empty.
  • find -perm 777 → displays files and folders with -rwxrwxrwx permissions.
  • find . -type f -name "name*" -exec rm -rf {'{}'} + → exec : execute the files and folder found by find command with another command, {} : place holder, + : add all the files.

Other Commands

• where/whereis → displays the location of the environment variables.
• .bashrc file consists of the commands which are automatically executed when bash terminal is opened.
  • It also has alias, which is a short user-defined command that the shell translates to another command. The variables in capitals are environmental variables.
  • temporary alias
  • permanent alias [adding it in ~/.bashrc file
• .profile file consist of all the environmental variable paths.
• $PATH → consists all directories of the environmental variables
• export is used to set temporary environmental variable
• chmod → used to change the access permissions of file.
  • Types of file permissions:
    1. Read(r) [value = 4]
    2. Write(w) [value = 2]
    3. Execute(x) [value = 1]
  • Types of users:
    1. User[u]
    2. Guest[g]
    3. Other[o]
  • chmod 777 → -rwxrwxrwx
  • chmod 124 → --x-w-r--
  • chmod 000 → ---------
• chown → change owner

Terminal Shortcuts:

• Ctrl + A → move to the beginning of the line
• Ctrl + E → move to the end of the line
• Ctrl + U → remove the whole command
• Ctrl + K → removes everything to right of the cursor.
• Ctrl + L → clears the terminal like clear command
• Tab → used to auto-complete
• ; → many commands together

Network Commands

• ping → allows to request website server and displays all the statistics
• wget → download files from the internet.
• nslookup → displays the IP address of a particular domain
• netstat → displays the ports that are listening
• curl ifconfig.me -s → displays the IP address of the user

User Commands

• whoami → displays the username
• hostname → displays the name of the Hostname
  • hostname -i → displays the IP Address
• useradd → adds new user
  • passwd → adds new password
  • userdel → deletes existing users
• uname → displays the kernel name
  • uname -o → displays the type
  • uname -m → displays the architecture
  • uname -r → displays the kernel version
• id → displays the group IDs
• getent group driptanil → checks if ‘driptanil’ group exists

System Information Commands

• df → shows the disk size and usage details
  • df -h → displays the size and usage details in human readable format.
• du → shows the disk usage statistics in working directory
  • du -h → shows the disk usage statistics in working directory in human readable format.
• cat /etc/os-release → displays the operation system information
• lscpu → displays the CPU details
• free → displays the memory statistics
• vmstat → displays the virtual memory statistics

Managing Tasks Commands

• top → shows all the processes running
• kill → kills the process with the specified process ID.
• jobs → displays the running commands
• ps aux → the processes and the process ID
• htop → shows the processes which are using the resources

Operators

• Ampersand & → This command sends a process/script/command to the background.

  • to kill this background process use ps and kill command.

• Pipe | → The output of the first command acts as input to the second command

• && → executes the second command if and only if the first command is executed successfully.

• || → executes the second command if and only if the first command fails.

• ! → not operator

• >> → append

• > → over-write

• Combination (...) → group commands using ;