Bash Linux

1---
2name: bash-linux
3description: Bash/Linux terminal patterns. Critical commands, piping, error handling, scripting. Use when working on macOS or Linux systems.
4allowed-tools: Read, Write, Edit, Glob, Grep, Bash
5---
6 
7# Bash Linux Patterns
8 
9> Essential patterns for Bash on Linux/macOS.
10 
11---
12 
13## 1. Operator Syntax
14 
15### Chaining Commands
16 
17| Operator | Meaning | Example |
18|----------|---------|---------|
19| `;` | Run sequentially | `cmd1; cmd2` |
20| `&&` | Run if previous succeeded | `npm install && npm run dev` |
21| `\|\|` | Run if previous failed | `npm test \|\| echo "Tests failed"` |
22| `\|` | Pipe output | `ls \| grep ".js"` |
23 
24---
25 
26## 2. File Operations
27 
28### Essential Commands
29 
30| Task | Command |
31|------|---------|
32| List all | `ls -la` |
33| Find files | `find . -name "*.js" -type f` |
34| File content | `cat file.txt` |
35| First N lines | `head -n 20 file.txt` |
36| Last N lines | `tail -n 20 file.txt` |
37| Follow log | `tail -f log.txt` |
38| Search in files | `grep -r "pattern" --include="*.js"` |
39| File size | `du -sh *` |
40| Disk usage | `df -h` |
41 
42---
43 
44## 3. Process Management
45 
46| Task | Command |
47|------|---------|
48| List processes | `ps aux` |
49| Find by name | `ps aux \| grep node` |
50| Kill by PID | `kill -9 <PID>` |
51| Find port user | `lsof -i :3000` |
52| Kill port | `kill -9 $(lsof -t -i :3000)` |
53| Background | `npm run dev &` |
54| Jobs | `jobs -l` |
55| Bring to front | `fg %1` |
56 
57---
58 
59## 4. Text Processing
60 
61### Core Tools
62 
63| Tool | Purpose | Example |
64|------|---------|---------|
65| `grep` | Search | `grep -rn "TODO" src/` |
66| `sed` | Replace | `sed -i 's/old/new/g' file.txt` |
67| `awk` | Extract columns | `awk '{print $1}' file.txt` |
68| `cut` | Cut fields | `cut -d',' -f1 data.csv` |
69| `sort` | Sort lines | `sort -u file.txt` |
70| `uniq` | Unique lines | `sort file.txt \| uniq -c` |
71| `wc` | Count | `wc -l file.txt` |
72 
73---
74 
75## 5. Environment Variables
76 
77| Task | Command |
78|------|---------|
79| View all | `env` or `printenv` |
80| View one | `echo $PATH` |
81| Set temporary | `export VAR="value"` |
82| Set in script | `VAR="value" command` |
83| Add to PATH | `export PATH="$PATH:/new/path"` |
84 
85---
86 
87## 6. Network
88 
89| Task | Command |
90|------|---------|
91| Download | `curl -O https://example.com/file` |
92| API request | `curl -X GET https://api.example.com` |
93| POST JSON | `curl -X POST -H "Content-Type: application/json" -d '{"key":"value"}' URL` |
94| Check port | `nc -zv localhost 3000` |
95| Network info | `ifconfig` or `ip addr` |
96 
97---
98 
99## 7. Script Template
100 
101```bash
102#!/bin/bash
103set -euo pipefail  # Exit on error, undefined var, pipe fail
104 
105# Colors (optional)
106RED='\033[0;31m'
107GREEN='\033[0;32m'
108NC='\033[0m'
109 
110# Script directory
111SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
112 
113# Functions
114log_info() { echo -e "${GREEN}[INFO]${NC} $1"; }
115log_error() { echo -e "${RED}[ERROR]${NC} $1" >&2; }
116 
117# Main
118main() {
119    log_info "Starting..."
120    # Your logic here
121    log_info "Done!"
122}
123 
124main "$@"
125```
126 
127---
128 
129## 8. Common Patterns
130 
131### Check if command exists
132 
133```bash
134if command -v node &> /dev/null; then
135    echo "Node is installed"
136fi
137```
138 
139### Default variable value
140 
141```bash
142NAME=${1:-"default_value"}
143```
144 
145### Read file line by line
146 
147```bash
148while IFS= read -r line; do
149    echo "$line"
150done < file.txt
151```
152 
153### Loop over files
154 
155```bash
156for file in *.js; do
157    echo "Processing $file"
158done
159```
160 
161---
162 
163## 9. Differences from PowerShell
164 
165| Task | PowerShell | Bash |
166|------|------------|------|
167| List files | `Get-ChildItem` | `ls -la` |
168| Find files | `Get-ChildItem -Recurse` | `find . -type f` |
169| Environment | `$env:VAR` | `$VAR` |
170| String concat | `"$a$b"` | `"$a$b"` (same) |
171| Null check | `if ($x)` | `if [ -n "$x" ]` |
172| Pipeline | Object-based | Text-based |
173 
174---
175 
176## 10. Error Handling
177 
178### Set options
179 
180```bash
181set -e          # Exit on error
182set -u          # Exit on undefined variable
183set -o pipefail # Exit on pipe failure
184set -x          # Debug: print commands
185```
186 
187### Trap for cleanup
188 
189```bash
190cleanup() {
191    echo "Cleaning up..."
192    rm -f /tmp/tempfile
193}
194trap cleanup EXIT
195```
196 
197---
198 
199> **Remember:** Bash is text-based. Use `&&` for success chains, `set -e` for safety, and quote your variables!
200