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
| 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
8. Common Patterns
Check if command exists
Default variable value
Read file line by line
Loop over files
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
Trap for cleanup
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.