This cheatsheet provides quick examples and explanations for essential Linux commands and bash scripting constructs with command output simulations for better understanding.

📁 File & Directory Commands

ls – List files 

$ ls
file1.txt  folder1  script.sh

ls -ltr – Long format, sorted by modification time (reverse) 

$ ls -ltr
-rw-r--r-- 1 user user   0 Apr 14 10:01 file1.txt
drwxr-xr-x 2 user user 4096 Apr 14 10:02 folder1

mkdir folder_name – Create a new directory 

$ mkdir myfolder

touch file_name – Create a new empty file 

$ touch myfile.txt

cat file_name – Read and display contents of a file 

$ cat myfile.txt
Hello, World!

man command – Show manual for any command 

$ man ls
# Opens the manual for 'ls'

vim filename / vi filename – Open file in Vim editor 

$ vim myfile.txt

Vim Modes

  • ESC + i – Enter insert mode
  • ESC + :wq! – Save and quit forcefully

pwd – Print current working directory 

$ pwd
/home/user/projects

cd folder_name – Change directory 

$ cd myfolder

🔒 File Permissions

chmod – Change file access permissions

Permissions are represented as:

  • 4 – Read
  • 2 – Write
  • 1 – Execute

To give all access to everyone:

$ chmod 777 myfile.txt

This gives read, write, and execute permissions to:

  • Owner
  • Group
  • Others

🗑 Delete

rm -rf folder_name – Force delete a folder recursively 

$ rm -rf temp_folder

🧠 System Info

nproc – Show number of CPU cores 

$ nproc
8

free – Show memory usage 

$ free -h
              total        used        free
Mem:           15Gi        4Gi         11Gi

top – Live system monitoring 

$ top
# Shows CPU, memory usage and running processes in real time

df -h – Show disk usage in human-readable format 

$ df -h
Filesystem      Size  Used Avail Use%
/dev/sda1       100G   50G   50G  50%

⚙️ Process Management

ps -ef – Show all running processes 

$ ps -ef
UID   PID  PPID  CMD
root    1     0   /sbin/init

ps -ef | grep "amazon" – Filter processes with 'amazon' 

$ ps -ef | grep "amazon"
user  2345  1234  /usr/bin/amazon

| – Pipe output from one command to another

Used to filter or chain commands

grep – Filter lines from output 

$ cat log.txt | grep "error"
[ERROR] Something went wrong!

awk – Extract fields 

$ ps -ef | grep amazon | awk -F" " '{print $2}'
2345

🐛 Debugging & Safe Scripting

set -x – Enable debug mode (prints each command before executing)

set -e – Exit script on any command failure (except in a pipeline)

set -o pipefail – Also fail if any part of a pipeline fails

🌐 Network Commands

curl {log_file_url} | grep error – Get a log file and search for 'error' 

$ curl http://example.com/log.txt | grep error
[ERROR] Out of memory

curl -X GET {url} – Send GET request 

$ curl -X GET https://api.example.com/data

wget {url} – Download a file 

$ wget https://example.com/file.zip

🔍 Search

sudo find / -name filename – Search for a file in entire system 

$ sudo find / -name myfile.txt
/home/user/docs/myfile.txt

🔁 Bash Scripting Basics

if statement 

if [ condition ]
then
  echo "Condition is true"
else
  echo "Condition is false"
fi

for loop 

for i in {1..100}; do
  echo $i
done

kill -9 PID – Force kill a process 

$ kill -9 1234

trap – Catch signals like CTRL+C 

trap "echo 'Don't use CTRL+C'" SIGINT

(Dangerous!) 

trap "rm -rf *" SIGINT

⚠️ Be extremely careful. This will delete everything on CTRL+C!

✅ Notes

  • Always test chmod, rm, and trap with caution.
  • Prefer vim over vi as it's more feature-rich.
  • Use set -euxo pipefail for safe and debuggable scripts.

📘 This README is designed to be a beginner-friendly cheatsheet. Contributions and suggestions welcome!

Made with ❤️ by Kishgi