Bash & Linux Reference

Commands, concepts, and cheat sheets - everything you need for the terminal

One-Liners

Cheat Sheet

Copy-paste ready one-liners for everyday tasks.

Find & Delete

# Delete all .pyc files recursively
find . -name "*.pyc" -delete

# Delete all __pycache__ directories
find . -type d -name "__pycache__" -exec rm -rf {} +

# Delete files older than 30 days
find /tmp -type f -mtime +30 -delete

Count & Measure

# Count lines of code (excluding blanks)
find . -name "*.py" | xargs cat | grep -v '^$' | wc -l

# Count files by extension
find . -type f | sed 's/.*\.//' | sort | uniq -c | sort -rn

# Largest files in directory
du -ah . | sort -rh | head -20

Search & Replace

# Find files containing a string
grep -rl "old_function" src/

# Replace string across all files
find . -name "*.py" -exec sed -i 's/old_func/new_func/g' {} +

# Search and show context
grep -rn -C 3 "ERROR" /var/log/

Process Management

# Kill all processes on a port
lsof -ti:3000 | xargs kill -9

# Watch a command every 2 seconds
watch -n 2 'df -h'

# Run command and get notification when done
long_command; echo "Done!" | mail -s "Task complete" you@email.com

Frequently Asked Questions

What is the best way to learn Bash scripting?

Start with simple automation: backup scripts, log parsers, deployment scripts. Use shellcheck to catch common mistakes. Practice by replacing manual terminal workflows with scripts.

How do I debug a Bash script?

Use set -x to print each command before execution. Add set -euo pipefail at the top to catch errors. Use shellcheck for static analysis. Echo variables at key points.

What text processing tool should I use: grep, sed, or awk?

grep for finding/filtering lines, sed for find-and-replace, awk for column-based data processing. Often you chain them: grep to filter, awk to extract, sort to organize.

How do I make curl requests with authentication?

Use -u user:pass for basic auth, -H "Authorization: Bearer TOKEN" for token auth, or -b cookies.txt for cookie-based auth.

What is the difference between bash and sh?

sh (Bourne shell) is the POSIX standard. bash (Bourne Again Shell) extends it with arrays, [[ ]], string manipulation, and more. Most Linux systems use bash, but scripts targeting portability should use #!/bin/sh.

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