GPT-Generated Bash Scripts

Prompt engineering techniques for generating reliable, production-safe bash scripts with AI.

Category: AI / GPT

The Golden Prompt Template

Write a bash script for Ubuntu 22.04 that:
1. [Primary task]
2. [Error handling requirement]
3. [Logging requirement]
4. [Safety requirement — e.g. dry-run mode]

Requirements:
- Use set -euo pipefail
- Include comments explaining non-obvious steps
- Test for required binaries before running
- Return exit code 0 on success, 1 on failure

Example: Disk Cleanup Script

Prompt sent to GPT:

Write a bash script for Ubuntu 22.04 that:
1. Finds log files older than 30 days in /var/log and /home/*/logs
2. Prints a summary of what will be deleted (dry-run by default)
3. Accepts a --delete flag to actually remove the files
4. Logs deleted files to /var/log/cleanup.log with timestamps

GPT output (condensed):

#!/bin/bash
set -euo pipefail

DRY_RUN=true
LOG="/var/log/cleanup.log"
DIRS=("/var/log" /home/*/logs)

[[ "${1:-}" == "--delete" ]] && DRY_RUN=false

for dir in "${DIRS[@]}"; do
  [[ -d "$dir" ]] || continue
  while IFS= read -r file; do
    size=$(du -sh "$file" 2>/dev/null | cut -f1)
    echo "[$(date)] Found: $file ($size)"
    if ! $DRY_RUN; then
      rm -f "$file"
      echo "[$(date)] DELETED: $file" >> "$LOG"
    fi
  done < <(find "$dir" -type f -name "*.log" -mtime +30)
done

Common Follow-Up Prompts

• "Add a --help flag that explains usage"
• "Make it send a Slack notification on failure"
• "Rewrite this to work on both Ubuntu and RHEL"
• "Add a lock file so it can't run twice at the same time"

Validating AI-Generated Scripts

• Run shellcheck script.sh to catch common errors
• Test with bash -n script.sh for syntax errors
• Run in a Docker container first: docker run -it ubuntu:22.04 bash