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+---
+name: bash-linux
+description: "Bash/Linux terminal patterns. Critical commands, piping, error handling, scripting. Use when working on macOS or Linux systems."
+risk: unknown
+source: community
+date_added: "2026-02-27"
+---
+
+# Bash Linux Patterns
+
+> Essential patterns for Bash on Linux/macOS.
+
+---
+
+## 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"` |
+
+---
+
+## 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` |
+
+---
+
+## 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` |
+
+---
+
+## 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` |
+
+---
+
+## 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"` |
+
+---
+
+## 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` |
+
+---
+
+## 7. Script Template
+
+```bash
+#!/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} $1" >&2; }
+
+# Main
+main() {
+    log_info "Starting..."
+    # Your logic here
+    log_info "Done!"
+}
+
+main "$@"
+```
+
+---
+
+## 8. Common Patterns
+
+### Check if command exists
+
+```bash
+if command -v node &> /dev/null; then
+    echo "Node is installed"
+fi
+```
+
+### Default variable value
+
+```bash
+NAME=${1:-"default_value"}
+```
+
+### Read file line by line
+
+```bash
+while IFS= read -r line; do
+    echo "$line"
+done < file.txt
+```
+
+### Loop over files
+
+```bash
+for file in *.js; do
+    echo "Processing $file"
+done
+```
+
+---
+
+## 9. Differences from PowerShell
+
+| Task | PowerShell | Bash |
+|------|------------|------|
+| List files | `Get-ChildItem` | `ls -la` |
+| Find files | `Get-ChildItem -Recurse` | `find . -type f` |
+| Environment | `$env:VAR` | `$VAR` |
+| String concat | `"$a$b"` | `"$a$b"` (same) |
+| Null check | `if ($x)` | `if [ -n "$x" ]` |
+| Pipeline | Object-based | Text-based |
+
+---
+
+## 10. Error Handling
+
+### Set options
+
+```bash
+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
+
+```bash
+cleanup() {
+    echo "Cleaning up..."
+    rm -f /tmp/tempfile
+}
+trap cleanup EXIT
+```
+
+---
+
+> **Remember:** Bash is text-based. Use `&&` for success chains, `set -e` for safety, and quote your variables!
+
+## When to Use
+This skill is applicable to execute the workflow or actions described in the overview.
+
+## Limitations
+- Use this skill only when the task clearly matches the scope described above.
+- Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
+- Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.