bash-linux

name	bash-linux
description	Bash/Linux terminal patterns. Critical commands, piping, error handling, scripting. Use when working on macOS or Linux systems. When working on macOS or Linux systems, writing bash scripts, or using terminal commands. NOT for Windows/PowerShell environments.
allowed-tools	Read, Write, Edit, Glob, Grep, Bash

Bash Linux Patterns

Essential patterns for Bash on Linux/macOS.

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1. Operator Syntax

Chaining Commands

Operator	Meaning	Example
;	Run sequentially	cmd1; cmd2
&&	Run if previous succeeded	npm install && npm run dev
||	Run if previous failed	npm test || echo "Tests failed"
|	Pipe output	ls | grep ".js"

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2. File Operations

Essential Commands

Task	Command
List all	ls -la
Find files	find . -name "*.js" -type f
File content	cat file.txt
First N lines	head -n 20 file.txt
Last N lines	tail -n 20 file.txt
Follow log	tail -f log.txt
Search in files	grep -r "pattern" --include="*.js"
File size	du -sh *
Disk usage	df -h

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3. Process Management

Task	Command
List processes	ps aux
Find by name	ps aux | grep node
Kill by PID	kill -9 <PID>
Find port user	lsof -i :3000
Kill port	kill -9 $(lsof -t -i :3000)
Background	npm run dev &
Jobs	jobs -l
Bring to front	fg %1

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4. Text Processing

Core Tools

Tool	Purpose	Example
grep	Search	grep -rn "TODO" src/
sed	Replace	sed -i 's/old/new/g' file.txt
awk	Extract columns	awk '{print $1}' file.txt
cut	Cut fields	cut -d',' -f1 data.csv
sort	Sort lines	sort -u file.txt
uniq	Unique lines	sort file.txt | uniq -c
wc	Count	wc -l file.txt

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5. Environment Variables

Task	Command
View all	env or printenv
View one	echo $PATH
Set temporary	export VAR="value"
Set in script	VAR="value" command
Add to PATH	export PATH="$PATH:/new/path"

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6. Network

Task	Command
Download	curl -O https://example.com/file
API request	curl -X GET https://api.example.com
POST JSON	curl -X POST -H "Content-Type: application/json" -d '{"key":"value"}' URL
Check port	nc -zv localhost 3000
Network info	ifconfig or ip addr

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7. Script Template

#!/bin/bash
set -euo pipefail  # Exit on error, undefined var, pipe fail

# Colors (optional)
RED='\033[0;31m'
GREEN='\033[0;32m'
NC='\033[0m'

# Script directory
SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"

# Functions
log_info() { echo -e "${GREEN}[INFO]${NC} $1"; }
log_error() { echo -e "${RED}[ERROR]${NC} $1" >&2; }

# Main
main() {
    log_info "Starting..."
    # Your logic here
    log_info "Done!"
}

main "$@"

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8. Common Patterns

Check if command exists

if command -v node &> /dev/null; then
    echo "Node is installed"
fi

Default variable value

NAME=${1:-"default_value"}

Read file line by line

while IFS= read -r line; do
    echo "$line"
done < file.txt

Loop over files

for file in *.js; do
    echo "Processing $file"
done

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9. Differences from PowerShell

Task	PowerShell	Bash
List files	Get-ChildItem	ls -la
Find files	Get-ChildItem -Recurse	find . -type f
Environment	$env:VAR	$VAR
String concat	"$a$b"	"$a$b" (same)
Null check	if ($x)	if [ -n "$x" ]
Pipeline	Object-based	Text-based

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10. Error Handling

Set options

set -e          # Exit on error
set -u          # Exit on undefined variable
set -o pipefail # Exit on pipe failure
set -x          # Debug: print commands

Trap for cleanup

cleanup() {
    echo "Cleaning up..."
    rm -f /tmp/tempfile
}
trap cleanup EXIT

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Remember: Bash is text-based. Use && for success chains, set -e for safety, and quote your variables!