Hashline Rust Tools

This skill provides a small CLI (hashline) that implements:

• read: prints file contents with hashline prefixes LINE:HASH|content
• edit: applies a list of hash-verified edits (set_line, replace_lines, insert_after, optional replace)

The goal is fail-fast edits: if the file changed since the agent last read it, anchors won’t match and the edit will be rejected.

Build

If hashline is already on your PATH (for example installed via Nix/Home Manager), skip this section.

Otherwise, from the skill directory:

cd ~/.codex/skills/hashline
cargo build

Binary path:

~/.codex/skills/hashline/target/debug/hashline

Read

hashline read path/to/file.txt

Optional:

hashline read path/to/file.txt --offset 10 --limit 50

Output format:

12:1a2b|some line content
13:9f00|next line

Use the LINE:HASH part (example 13:9f00) as anchors in edits.

Edit

Edits JSON can be either an array of edit objects, or an object with { "edits": [...] }.

1) Set (replace) a single line

hashline edit path/to/file.txt --edits-json '
[
  {"set_line": {"anchor": "3:abcd", "new_text": "replaced content"}}
]
'

• new_text may contain \n to replace the single line with multiple lines.
• new_text: "" deletes that line.

2) Replace a range of lines

hashline edit path/to/file.txt --edits-json '
[
  {"replace_lines": {"start_anchor": "5:aaaa", "end_anchor": "8:bbbb", "new_text": "new block\nsecond line"}}
]
'

• new_text: "" deletes the whole range.

3) Insert after a line

hashline edit path/to/file.txt --edits-json '
[
  {"insert_after": {"anchor": "10:ccdd", "text": "inserted line"}}
]
'

4) Content replace (no anchors)

This is optional and runs after anchor-based edits.

hashline edit path/to/file.txt --edits-json '
[
  {"replace": {"old_text": "foo", "new_text": "bar", "all": true}}
]
'

Preview

hashline edit path/to/file.txt --edits-file edits.json --preview

Agent usage pattern

1. hashline read <file>
2. Select the exact line anchors you will target.
3. Call hashline edit <file> --edits-json ... with those anchors.
4. If you get a “changed since last read” error, re-read and retry with updated anchors.