/bash-linux

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` |

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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` |

---

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 "$@"

---

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

---

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

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

---

> **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.