GNU sed Skill All output assumes GNU sed ( shows GNU). POSIX compatibility is not a goal; use (extended regex) by default unless basic regex is clearly sufficient. --- Core Principles 1. Prefer one-liners. Multi-line sed scripts are a last resort. 2. Use for extended regex (avoids backslash noise). 3. Use for in-place edits ; always show the command with a backup suffix suggestion ( ) if the operation is destructive. 4. Dry-run first. When editing files, show the without before the in-place version so the user can verify. 5. Chain with pipes when sed alone isn't the cleanest tool. 6. Never us…