Command Line

pwdPrint Working Directory

Shows the absolute path of your current working directory.

Examples

pwd

Example output:

/home/yourname/Projects

lsList

Lists files and directories in the current directory.

Examples

ls

ls -a

ls -l

ls -la

Common Options

-a

Includes hidden files and directories.

-l

Uses a detailed listing format.

-h

Displays file sizes in a human-readable format when used with -l.

Useful Example

ls -lah

Shows hidden files using a detailed, human-readable listing.

cdChange Directory

Changes the current working directory.

Examples

cd ~/Projects

cd ..

cd /home/yourname

cd /

cd ~

Special Paths

~

Your home directory.

.

The current directory.

..

The parent directory.

/

The root directory.

Useful Example

cd ~/Projects

pwd

mkdirMake Directory

Creates one or more directories.

Examples

mkdir my-folder

mkdir project docs

Useful Option

mkdir -p project/src/components

The -p option creates parent directories when they do not already exist.

touchCreate or Update a File

Creates an empty file if it does not exist. If the file already exists, it updates its modification timestamp.

touch README.md

touch index.html style.css script.js

catConcatenate / Display

Displays the contents of one or more files in the terminal.

cat README.md

cat file1.txt file2.txt

It is useful for quickly viewing small files.

lessView Files Page by Page

Opens a file in a scrollable terminal viewer. It is useful for reading large files.

less README.md

less large-file.log

Press q to exit.

echoPrint Text

Prints text or the value of a variable to standard output.

echo "Hello, world"

echo "$HOME"

Redirection

echo "Hello" > myfile.txt

echo "More text" >> myfile.txt

>

Writes output to a file, replacing its existing contents.

>>

Appends output to the end of a file.

cpCopy

Copies files or directories from one location to another.

cp file.txt backup.txt

cp file.txt ~/Documents/

Copy a Directory

cp -r project project-backup

The -r option copies a directory and its contents recursively.

mvMove / Rename

Moves a file or directory. It can also be used to rename them.

mv file.txt Documents/

mv old-name.txt new-name.txt

rmRemove

Removes files or directories.

rm file.txt

Remove a Directory

rm -r old-folder

Be careful with rm: removed files are generally not moved to a recycle bin.

clearClear the Terminal

Clears the visible contents of the terminal screen.

clear

manManual

Opens the manual page for a command.

man ls

man mkdir

man cp

Manual pages are one of the primary ways to learn how Unix commands work.

whichLocate an Executable

Shows the path of the executable that the shell would run for a command.

which python

which git

which bash

whoamiCurrent User

Displays the username of the current user.

whoami

dateDisplay Date and Time

Displays the current system date and time.

date

historyCommand History

Displays commands that were previously entered in the shell.

history

You can usually press the ↑ and ↓ arrow keys to navigate through previous commands.

grepSearch Text

Searches for matching text within files or command output.

grep "error" app.log

grep -i "hello" file.txt

Common Option

-i

Ignores differences between uppercase and lowercase letters.

findFind Files and Directories

Searches for files and directories based on conditions such as name, type, or modification time.

find . -name "*.html"

find . -type f

find . -type d

sortSort Text

Sorts lines of text alphabetically or according to other rules.

sort names.txt

wcCount

Counts lines, words, and bytes in files or input.

wc file.txt

wc -l file.txt

The -l option counts lines.

headShow the Beginning

Displays the beginning of a file. By default, it shows the first 10 lines.

head file.txt

head -n 20 file.txt

tailShow the End

Displays the end of a file. It is particularly useful for inspecting log files.

tail app.log

tail -n 20 app.log

Follow a Log

tail -f app.log

The -f option continues displaying new lines as they are added to the file.

psProcesses

Displays information about running processes.

ps

ps aux

killSend a Signal to a Process

Sends a signal to a process, commonly to request that it stop.

kill 1234

The number is the process ID (PID).

chmodChange Permissions

Changes the permissions associated with a file or directory.

chmod +x script.sh

This example adds execute permission to the script.

envEnvironment

Displays environment variables or runs a command with modified environment variables.

env

echo "$HOME"

echo "$PATH"

exportSet Environment Variables

Creates or modifies an environment variable for the current shell and processes started from it.

export NAME="yourname"

echo "$NAME"

commandRun a Command

Can be used to check or execute commands using shell built-in functionality.

command -v git

command -v python

Output Redirection: >

Sends standard output to a file and replaces the file's existing contents.

echo "Hello" > output.txt

Append Output: >>

Sends standard output to a file and appends to its existing contents.

echo "Another line" >> output.txt

Pipe: |

Sends the output of one command directly into another command.

ls -la | grep ".html"

Here, ls -la produces output and grep searches that output.

Combine Commands

cat names.txt | sort | uniq

The output flows from one command into the next.