# Bash Linux

> ALWAYS use this when the user mentions Bash Linux, asks to build, debug, review, document, automate, test, configure, migrate, or make decisions in this domain, or the task clearly depends on Bash Linux; scope: Bash/Linux terminal patterns. Apply the bundled workflow, references, scripts, Senior Master standard, and Codex strict review gate before final output.

- Skill: `anhvu1107/bash-linux` (Agent Skill, multi-file: 6 files)
- Install (CLI): `npx skillmds@latest add anhvu1107/bash-linux`
- Raw SKILL.md: https://api.skillmd.com/api/skills/anhvu1107/bash-linux/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: anhvu1107 (https://skillmd.com/u/anhvu1107)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/anhvu1107/bash-linux

---


# Bash Linux Patterns

## Selective Reading Rule

Start with:

- `references/senior-master-standard.md`
- `references/usage-routing.md`
- `references/quality-checklist.md`

Then load only the inherited docs, scripts, assets, or examples that match the user's actual task.

> 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!