Bash One Pager

#tutorial #bash #linux

This is a one-page reference for the top Bash commands and tricks. It covers everything from basic file operations to intermediate shell scripting.

File Operations

Essential commands for manipulating files.

Command Description
ls -lah List all files (including hidden) with human-readable sizes.
cp -r source dest Copy files or directories recursively.
mv source dest Move or rename a file/directory.
rm -rf path Danger: Forcefully remove a directory and its contents.
touch file.txt Create an empty file or update its timestamp.
cat file.txt Output the entire content of a file.
less file.txt View file content one page at a time (q to quit).
head -n 10 file View the first 10 lines of a file.
tail -f file.log Follow the output of a file as it grows (great for logs).
find . -name "*.js" Find files ending in .js in the current directory.

Directory Operations

Navigating the filesystem.

Command Description
pwd Print Working Directory (where am I?).
cd /path/to/dir Change directory.
cd .. Go up one directory level.
cd ~ Go to the user's home directory.
cd - Go back to the previous directory you were in.
mkdir -p a/b/c Create a nested directory tree in one go.
tree -L 2 Show directory structure as a tree (max depth 2).

Disk, CPU, and Memory

Checking system resources.

Command Description
df -h Show Disk Free space in human-readable format.
du -sh folder/ Show Disk Usage summary for a specific folder.
free -h Show available RAM and Swap memory.
top Live view of system processes and resource usage.
htop A prettier, more interactive version of top (if installed).
uptime Show how long the system has been running and load averages.

Process Management

Viewing and controlling running programs.

Command Description
ps aux List all running processes for all users.
ps aux | grep node Find a specific process (e.g., node).
pidof app_name Get the ID (PID) of a specific program.
kill 1234 Terminate process with PID 1234.
kill -9 1234 Force kill process 1234 (use carefully).
killall nginx Kill all processes named nginx.
bg / fg Send a job to background or bring to foreground.
Ctrl + Z Suspend the current foreground process.

Users and Environment

Who are you and where are you?

Command Description
whoami Display current username.
id Show user ID and group IDs.
sudo command Run command as root (SuperUser).
su - username Switch to another user environment.
env List all environment variables.
export VAR=value Set an environment variable.
echo $PATH Print the executable search path.
history Show command history.

Network & Host Info

Connectivity and identity.

Command Description
hostname -I Display the host's IP address(es).
ping google.com Check connectivity to a host.
curl -I example.com Fetch HTTP headers from a URL.
wget url Download a file from the web.
netstat -tuln Show active listening ports (TCP/UDP).
ss -tulpn Modern replacement for netstat.
ssh user@host Secure Shell: Connect to a remote server.
scp file user@host:~ Secure Copy: Upload file to remote home dir.

Date, Time, & Scheduling

Command Description
date Show current date and time.
date -u Show time in UTC.
cal Show a calendar for the current month.
crontab -e Edit cron jobs (scheduled tasks).
crontab -l List current cron jobs.
at 5pm Schedule a one-time job for 5 PM.

Bash Scripting Basics

Top syntax patterns for writing .sh scripts.

Variables & I/O

#!/bin/bash

# Definition (no spaces!)
NAME="John"
COUNT=5

# Usage
echo "Hello, $NAME"
echo "Count is ${COUNT}"

# Reading Input
read -p "Enter your age: " AGE
echo "You are $AGE years old."