DevOps

Linux & Terminal Commands

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

Driptanil DattaSoftware Developer

Mar 202510 min read

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 ;

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