exhash: Verified Line-Addressed File Editor

exhash combines Can Bölük's very clever line number + hash editing system with the powerful and expressive syntax of the classic ex editor.

Install via pip to get a convenient Python API, an IPython cell magic, and the exhash/lnhashview CLI commands:

pip install exhash

lnhash format

We refer to an lnhash as a tag of the form lineno|hash|, where hash is the low 12 bits of CRC-32 (IEEE) over the line's UTF-8 content, encoded as two Base64url characters (A–Z, a–z, 0–9, -, _), high six bits first.

Address forms:

• lineno|hash|: hash-verified address
• $: last line (no hash)
• %: whole file (1,$, no hashes)
• lineno: line number with no hash. Only p accepts it, including as the subcommand of g, g!, or v.

CLI

The exhash and lnhashview commands are Python console scripts over the native Rust extension, installed into your PATH by pip.

View

# Shows every line prefixed with its lnhash
lnhashview path/to/file.txt
# Optional line number range to show
lnhashview path/to/file.txt 10 20

If end is past EOF, lnhashview returns through the last available line instead of failing.

Edit

# Substitute on one line
exhash file.txt '12|vN|s/foo/bar/g'

# Transliterate characters on one line
exhash file.txt '12|vN|y/abc/ABC/'

# Change one line with inline text (spaces after c are literal text)
exhash file.txt '12|vN|c    replacement line'

# Append multiline text from stdin (read through EOF; every line is literal)
exhash file.txt '12|vN|a' <<'EOF'
new line 1
new line 2
EOF

# Dry-run
exhash --dry-run file.txt '12|vN|d'

# Set shift width for < and >
exhash --sw 2 file.txt '12|vN|>1'

# Last line and whole file shorthands (no hash)
exhash file.txt '$d'
exhash file.txt '%j'

# Print lines 12 to 20: p accepts line numbers with no hashes
exhash file.txt '12,20p'

# Move a line to EOF using $ as the destination
exhash file.txt '12|vN|m$'

# Create a missing file by treating it as empty input
exhash new.txt '0|AA|a' <<'EOF'
first line
EOF

Substitute and global commands use fancy-regex syntax, including lookbehind ((?<=...), (?<!...)), lookahead ((?=...), (?!...)), and pattern backreferences (\1):

• Replacement syntax uses $1, $0, ${name}, and $$ for a literal dollar sign; \1 in a replacement stays literal. See fancy_regex::Regex::try_replacen.
• \/ escapes the command delimiter in pattern/replacement
• Custom delimiters: s, y, g, g!, and v all accept any non-alphanumeric char as delimiter instead of /, e.g. s@pat@rep@, g@pat@cmd. Each command in a combo picks its own delimiter independently: g@a/b@s/old/new/
• For example, s/// accepts newlines in pattern/replacement; replacement newlines split one line into multiple lines.
• Transliteration uses y/src/dst/ and requires source/destination to have equal character counts
• A substitute whose pattern matches nothing in its addressed range fails (nothing is written), so a typo cannot silently no-op; substitutes running inside g/g!/v payloads stay lenient, since not every selected line need match
• Matching errors, including exceeding the engine's default backtracking limit, abort the command set before any files are written

When passing multiple commands, each command's lnhashes are verified immediately before it runs. A single-line address may match either the line's current hash or its call-start hash, so commands can stack on one line. Range addresses remain strict, and structural changes invalidate call-start records at and below their topmost affected line.

For CLI multiline a/i/c commands, omit inline text and provide the text block on stdin:

printf "new line 1\nnew line 2\n" | exhash file.txt "2|7v|a"

If the file does not exist and the command set is valid on empty input, exhash treats it as an empty file and writes the result. For example, 0|AA|a can create a new file.

Stdin filter mode

cat file.txt | exhash --stdin - '1|vN|s/foo/bar/'

In --stdin mode, multiline a/i/c text blocks are not available.

Notebook cells

lnhashview-cell and exhash-cell apply the same workflow to notebook cells, addressed by exact or unique ID prefixes. Pass comma-separated IDs to view several cells together; the output adds a # cell <id> header to each group:

lnhashview-cell nbs/00_core.ipynb ab12cd34
lnhashview-cell nbs/00_core.ipynb ab12cd34,ef56ab78
exhash-cell nbs/00_core.ipynb ab12cd34 '3|7v|s/old/new/'
exhash-cell --dry-run nbs/00_core.ipynb ab12cd34 '3|7v|d'
printf 'replacement line\n' | exhash-cell nbs/00_core.ipynb ab12cd34 '3|7v|c'

Document outlines

exhash-open opens Markdown, source code, notebooks, URLs, or stdin as a verified section tree. Its default output is the immediate outline; copy a displayed token back to read that section:

exhash-open README.md
exhash-open README.md '1.2.|21|Z1|,101|Js|'
exhash-open README.md --paths --depth 2
exhash-open README.md --search 'CLI|console'
exhash-open README.md --lnhashs
exhash-open https://example.com/llms.txt --links

Python API

from exhash import exhash, file_exhash, lnhash, lnhashview, lnhashview_file, line_hash

Viewing

text = "foo\nbar\n"
view = lnhashview(text)                        # ["1|Gy|foo", "2|PU|bar"]
view = lnhashview_file("f.py", start=1, end=260) # end past EOF is clamped

lnhashview/lnhashview_file return a list subclass whose repr shows the rows verbatim, one per line, so a bare call in IPython displays a ready-to-copy view.

Editing

exhash(text, cmds, sw=4) takes the text and a required iterable of tuple command specs (use [] for no-op). Raw command strings are rejected by the Python API. sw controls how far < and > shift.

A command is usually (addr, op) or (addr, op, payload). addr is an lnhash address string from lnhash(...)/lnhashview(...); put ranges in that same string, e.g. f"{a1},{a2}". Substitute uses (addr, "s", pattern, replacement[, flags]), so patterns and replacements can contain / without delimiter escaping.

Text fields can contain newlines. That covers multiline a/i/c payloads and substitute pattern/replacement. In a/i/c payloads a trailing newline ends the last line, as in CLI stdin blocks: "x" and "x\n" both insert one line, "x\n\n" inserts x and then a blank line, and an empty payload is no lines, so c with "" deletes the addressed lines. Commands such as d, m, and sort do not take text.

addr = lnhash(1, "foo")  # "1|Gy|"
res = exhash(text, [(addr, "s", "foo", "baz")])
print(res["lines"])    # ["baz", "bar"]
print(res["modified"]) # [1]

# Multiple commands
a1, a2 = lnhash(1, "foo"), lnhash(2, "bar")
res = exhash(text, [(a1, "s", "foo", "FOO"), (a2, "s", "bar", "BAR")])

# Hashes are checked just-in-time per command.
# If earlier commands change/shift a later target line, recompute lnhash first.

# Change one line; leading spaces are part of the replacement
res = exhash(text, [(addr, "c", "    replacement line")])

# Append multiline text in one tuple payload (no dot terminator)
res = exhash(text, [(addr, "a", "new line 1\nnew line 2")])

# Wrong for the Python API: the trailing "." would be inserted literally
# res = exhash(text, [(addr, "a", "new line 1\nnew line 2\n.")])

# Also wrong: do not split the inserted text into separate cmds entries
# res = exhash(text, [(addr, "a"), "new line 1", "new line 2"])

# Change shift width for < and >
res = exhash(text, [(addr, ">", "1")], sw=2)

# Literal / needs no delimiter escaping in tuple substitute fields
res = exhash("a/b\n", [(lnhash(1, "a/b"), "s", "a/b", "c/d")])

# Literal newlines in replacement split one line into multiple lines
res = exhash("foo\n", [(lnhash(1, "foo"), "s", "foo", "bar\nbaz")])
print(res["lines"])  # ["bar", "baz"]

# Literal newlines in pattern can match across lines
a1, a2 = lnhash(1, "foo"), lnhash(2, "bar")
res = exhash("foo\nbar\n", [(f"{a1},{a2}", "s", "foo\nbar", "replaced")])

# Global commands take a pattern plus a nested subcommand tuple (no address)
res = exhash("keep\nTODO x\n", [("%", "g", "TODO", ("d",))])

# Transliterate takes source/dest fields (equal character counts)
res = exhash("abc\n", [(lnhash(1, "abc"), "y", "abc", "ABC")])

File helpers

lnhashview_file reads directly from one file path. All file paths, including file-qualified addresses, expand a leading ~ to your home directory. file_exhash(path, *cmds, sw=4, inplace=True) uses path as the default file context for unqualified addresses. Pass each command as its own tuple argument. Put file-qualified source and m/t destination addresses in the address/destination tuple fields:

view = lnhashview_file("file.py")

# By default, writes changed files after every command succeeds
# and returns the combined diff string.
diff = file_exhash("file.py", (addr, "s", "foo", "bar"))

# With inplace=False, files are unchanged and a FileSetEditResult is returned.
res = file_exhash("file.py", (addr, "s", "foo", "bar"), inplace=False)
print(res.changed)          # ["file.py"]
print(res["file.py"].lines)
print(res.format_diff())    # includes --- file.py / +++ file.py headers

# Missing files are treated as empty only when the command is valid on empty input.
diff = file_exhash("new.py", ("0|AA|", "a", "print('hi')"))

# File-qualified addresses can edit or transfer lines across files.
diff = file_exhash("src/a.py",
    ("src/a.py:24|8S|,38|De|", "m", "src/b.py:$"),
    (r"src/a.py:5|Gq|", "s", r"from \.b import old", r"from \.b import helper"))

A file prefix is separated from the address with :. Escape literal colons in filenames as \: and literal backslashes as \\.

file_exhash(..., inplace=False) returns a FileSetEditResult:

• res.files: dict of path to FileEditResult
• res.changed: changed paths, in first-touch order
• res.printed: paths with lines addressed by p (res[path].printed gives the line numbers)
• res.default_path: the default path passed to file_exhash
• res[path]: shorthand for res.files[path]
• res.format_diff(context=1): combined diff of the changed targets, with --- path / +++ path headers. It never includes printed lines.
• str(res): each target's diff, followed by its printed lines (see EditResult)

Notebook cells

lnhashview_cell(path, cell_id, ...) returns a normal lnhash view for one cell. lnhashview_cells(path, *cell_ids, ...) returns the requested cells in order, using # cell <id> headers before each cell's normal lineno|hash|content lines. cell_exhash(path, cell_id, *cmds, sw=4, inplace=True) edits one cell; pass each command as its own tuple argument. Like file_exhash it writes and returns a diff by default, and inplace=False previews the EditResult without touching the file.

The %%exhash cell magic

Importing exhash.skill under IPython or Jupyter registers the %%exhash cell magic - the standard way to apply a/i/c payload commands interactively. The magic line is %%exhash <path> [<cell_id>] <address> <a|i|c>; the payload is everything below it, taken verbatim. Nothing in the payload is parsed as Python, so there is no quoting or escaping at all:

%%exhash notes.txt 2|7v|a
new line 1
new line 2

• %%exhash new.py 0|AA| a creates a missing file.
• %%exhash f.py % c replaces the whole file (% needs no hashes). With a cell id, %%exhash nb.ipynb ab12 % c replaces that notebook cell's source.
• %%exhash f.py 12|Py|,15|HD| c replaces just that range, both addresses from one lnhashview_file view.
• A trailing newline ends the last line, as in every a/i/c payload; to end the payload with a blank line, leave an empty line at the bottom of the cell.
• Each magic cell applies one command and returns the diff.

Tuple a/i/c payloads (as in the examples above) remain for scripts and tests, where magics don't exist. Interactively, prefer the magic: a Python string layer invites quoting mistakes.

Pyskill

The package registers exhash.skill as a pyskill exposing the primary Python APIs with LLM-oriented workflow docs. Use doc(exhash.skill) after importing it through a pyskills host.

EditResult

exhash() returns an EditResult with attributes (also accessible via res["key"]):

• lines: list of output lines
• hashes: lnhash for each output line
• modified: 1-based line numbers of modified/added lines
• deleted: 1-based line numbers of removed lines (in original)
• origins: for each output line, the 1-based original line number (None if inserted)
• printed: 1-based line numbers explicitly addressed by p

Lines addressed by p are not part of the diff. res.format_printed() returns them as a bare lnhashview with no headers. It never caps or truncates its rows. str(res) and the repr show the diff, then a # printed header, then the printed lines. A result that changed nothing shows the printed lines alone, with no header. file_exhash and cell_exhash return the same output. A p-only call writes nothing and returns the bare view. A call that changes and prints nothing returns none: No changes., as fastcore's editors do. When more than one target is reported, a target with only printed lines is headed by # file <path> or # cell <id>.

res.format_diff(context=1) returns a unified-diff-style summary showing only changed lines with context. Each contiguous changed block shows all removed lines before all added lines:

res = exhash(text, [(addr, "s", "foo", "baz")])
print(res.format_diff())
# --- original
# +++ modified
# -1|Gy|foo
# +1|PU|baz
#  2|X2|bar

format_diff(maxlen=n) caps each diff row at n chars plus a closing …. Where a run of changed rows holds as many - rows as + rows, the nth - row pairs with the nth + row. A capped row of a pair starts 20 chars before the pair's first difference, with … after its address. Every other capped row keeps its start. The result reprs and the diffs that file_exhash and cell_exhash return use maxlen=180. truncate_diff then keeps up to 15 diff lines, sharing each changed block's remaining budget between removals and additions. Elision markers appear at each omitted run, in addition to those 15 lines.

All diff strings returned by format_diff, file_exhash, and cell_exhash are fastcore PrettyStrings, and the result objects' reprs show the diff too - so in IPython, ending a cell with the bare call displays the diff verbatim, no print needed.

Document outlines

open_doc opens a file (fname=, or a Path as src; recorded for refresh() and edits), a URL (an https?:// str, fetched), or any other str as text, and returns a Section tree: Markdown sections from headings, code sections (py, js, ts, tsx, rs, zig, swift) from tree-sitter definitions, and .ipynb sections from md-heading cells over cells. The bare repr is a fixed-width outline, one row per section. It lists the section itself and the two levels below it, not counting a level that holds only one section, such as a single H1:

1.6.|56|lq|,78|74| Release [725] Publishing is handled by GitHub Actions in `.github/workflows/ci.yml`…

The leading token is a verified address: the dotted addr (trailing dot; the root's is .) fused with the section's start,end lnhash boundary pair. at(token) navigates with the first hash verified, so a stale copy fails loudly; the boundary pair drops straight into a file_exhash range command, so a listing is also an edit address book. find(title), search(pat), paths(depth), and numeric indexing (d[1][6]) traverse the live tree; links(pat) lists inline links numbered document-wide, and open(n) opens link n as a new tree (fetched or read relative to base). Previews join lines with ¶ and render links as [text][n], so no URL is ever displayed. A markdown row's preview starts under its heading; a code row has no title, and its preview opens with the def line itself, signature included. view() returns a section's rendered text the same way (.src is the raw source); view(*tokens) returns the live sections at those verified addresses, displayed under # token headers when more than one; nums=/lnhashs= switch any view to stored lines with edit-ready addresses. Notebook section tokens carry the heading cell id, and view(lnhashs=True) emits cellid:lineno|hash| rows ready for cell_exhash.

search(pat) returns one hit per matching source line, not one row per section. Each 180-character row shows the containing section's verified token, the matching line's hash address, and a preview starting at that line and continuing across newlines as ¶, up to the section's end. Section tokens repeat when several lines in the same section match: copy the section token to view() to read the whole section, or use the line address to edit the hit. Notebook line addresses include the cell ID. Each hit exposes .section, .address, and .preview; slicing the results preserves their display format.

Tests

pytest -q