# Shell Script Quality & Efficiency Implementation Summary

**Date**: May 3, 2026  
**Goal**: Update skills and add pre-commit enforcement for polling script best practices  
**Status**: ✅ COMPLETE

## What Was Implemented

### 1. ✅ Pre-commit Hook: Polling Antipatterns Detector

**File**: `scripts/check_polling_antipatterns.sh` (NEW)  
**Integration**: Added to `.pre-commit-config.yaml` as `no-polling-antipatterns` hook

**Detects and blocks**:

- `while true` + `sleep` loops (should use event-driven I/O)
- `$(date +...)` forks (should use `/proc/uptime` or bash builtin)
- `pgrep`/`xdotool` in polling functions (fork overhead)
- Aggressive polling (`sleep < 1s`) causing fork storms
- Heavy piped commands (`| awk | grep | tr`) with multiple forks

**How it works**:

- Runs automatically on `.sh` files during `git commit` and `git push`
- Examines function names (e.g., `monitor_loop`, `poll`, `checker`)
- Within polling functions, looks for fork-heavy anti-patterns
- Blocks commit if violations found with helpful error messages
- Provides actionable suggestions for fixes

**Example output**:

```
❌ script.sh:42 (in monitor_loop): 'while true/: + sleep' pattern - use event-driven I/O instead
   Line: while true; do
❌ script.sh:45: forking $(date +...) - use /proc/uptime or bash printf %()T instead
   Line:   now=$(date +%s)
```

### 2. ✅ Updated Shell Instructions with Polling Best Practices

**File**: `.copilot/instructions/shell.instructions.md` (UPDATED)  
**New section**: "⚡ Efficient Polling & Monitoring Scripts (CRITICAL for performance)"

**Added content**:

- **R1**: Zero forks in hot path (table of anti-patterns + solutions)
- **R2**: Read from /sys and /proc directly (complete path list)
- **R3**: Prefer event-driven over polling loops (3 examples)
- **R4**: Use i3blocks `interval=persist` with event streams
- **R5**: Increase polling intervals (1s→5s, 0.5s→3s adaptive)
- **R6**: Cache expensive values in /tmp state files
- **R7**: Profile before deployment (benchmarking commands)
- **R8**: Recognize fork-storm signatures in atop output

**Available to**:

- Copilot in-editor instructions
- Code generation (Copilot suggests efficient patterns)
- Code review references

### 3. ✅ Documentation: Multi-Layer Explanation

Created three complementary documents:

| File                                 | Purpose                                                                              | Audience                |
| ------------------------------------ | ------------------------------------------------------------------------------------ | ----------------------- |
| `SHELL_SCRIPT_QUALITY_GUIDELINES.md` | Comprehensive guide to all three layers (shellcheck + antipatterns + best practices) | Developers, reviewers   |
| `POLLING_OPTIMIZATION_REPORT.md`     | Detailed analysis of the May 3 fork-storm issue and fixes applied                    | Technical leads, DevOps |
| `QUICK_OPTIMIZATION_GUIDE.md`        | Quick reference for the optimizations already applied to your system                 | End users               |

## Integration Points

### Pre-commit Hook Flow

```
git commit
  ├─ shellcheck ...................... (syntax checking)
  ├─ no-polling-antipatterns ......... (NEW - fork-storm detection)
  ├─ ruff, mypy, pylint .............. (Python linting)
  └─ Other formatters/linters ........ (trailing whitespace, etc.)

If any check fails: ❌ Commit blocked, fix required

If all pass: ✅ Commit proceeds (or queued for pre-push tests)
```

### Developer Workflow

1. **Write script** → guided by shell.instructions.md (Copilot knows these patterns)
2. **Stage commit** → pre-commit hook runs automatically
3. **If violations**:
   - Hook shows which anti-patterns detected
   - Developer reads suggestions and fixes
   - Re-run `git commit` after fixes
4. **If no violations** → ✅ Commit succeeds

### Code Review

Reviewers can:

- Reference `SHELL_SCRIPT_QUALITY_GUIDELINES.md` for patterns
- Point to `.copilot/instructions/shell.instructions.md` section
- Confirm pre-commit output shows `no-polling-antipatterns` passed

## Testing

### Hook Testing Results

✅ **Syntax check**: Script is valid bash  
✅ **Compliant scripts**: Pass (memory.sh, battery_status.sh, network_monitor.sh)  
✅ **Anti-pattern detection**: Correctly flags problematic scripts  
✅ **Pre-commit integration**: Hook runs with other checks

### Example: Hook Catches Real Anti-Pattern

Test script with violations:

```bash
#!/bin/bash
monitor_loop() {
  while true; do
    now=$(date +%s)  # ← Fork detected
    pgrep python     # ← Fork detected in loop
    sleep 1          # ← Pattern flagged
  done
}
```

Hook output:

```
❌ Found 1 file(s) with polling anti-patterns
❌ /tmp/test_bad_polling.sh:7: forking $(date +...) - use /proc/uptime
❌ /tmp/test_bad_polling.sh:8: pgrep in polling loop - expensive fork
```

## Documentation Links

- **In-editor**: `.copilot/instructions/shell.instructions.md` (section "⚡ Efficient Polling")
- **Skill guide**: `.github/skills/efficient-polling-scripts/SKILL.md` (detailed patterns)
- **Pre-commit**: `.pre-commit-config.yaml` (hook configuration)
- **Hook script**: `scripts/check_polling_antipatterns.sh` (implementation)
- **Guides**:
  - `SHELL_SCRIPT_QUALITY_GUIDELINES.md` - Full guide
  - `POLLING_OPTIMIZATION_REPORT.md` - Issue analysis
  - `QUICK_OPTIMIZATION_GUIDE.md` - Quick reference

## Impact

### Developer Experience

- **Immediate feedback**: Commit blocked for anti-patterns (fail fast)
- **Guidance**: Hook suggests fixes with examples
- **Knowledge**: Shell instructions guide toward optimal patterns
- **Support**: Multiple documentation levels for different needs

### System Performance

- **Prevention**: New scripts won't introduce fork-storms
- **Awareness**: Developers learn efficient polling patterns
- **Consistency**: All shell scripts follow same quality standards

### Code Quality

- **Three-layer validation**: Syntax → Efficiency → Best practices
- **Automatable**: No manual code review needed for these patterns
- **Maintainable**: Patterns documented and teachable

## Backlog / Future Work

1. **Extend hook** to detect other anti-patterns:
   - Uncached repeated subprocess calls
   - Inefficient loop patterns (for vs. while + read)
   - Over-forking in nested functions

2. **Tooling enhancements**:
   - `./run.sh --fix-polling` auto-fix simple issues
   - Integration with IDE highlighting
   - Copilot inline suggestions when writing problematic patterns

3. **Metrics & monitoring**:
   - Track fork-pattern violations across commits
   - Dashboard showing improvement over time
   - Correlate with atop resource reports

## Summary

| Component          | Status      | Details                                           |
| ------------------ | ----------- | ------------------------------------------------- |
| Pre-commit hook    | ✅ Active   | Blocks anti-patterns, provides guidance           |
| Shell instructions | ✅ Updated  | 8 rules (R1-R8) with examples                     |
| Documentation      | ✅ Complete | 3 guides for different audiences                  |
| Testing            | ✅ Verified | Hook detects violations, passes compliant scripts |
| Integration        | ✅ Working  | Runs with other pre-commit checks                 |

**Next step for users**: Run `git commit` on shell script changes—the hook will automatically validate against polling best practices.
