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 lower 16 bits of Rust's DefaultHasher over the line content.

Address forms:

• lineno|hash|: hash-verified address
• $: last line (no hash)
• %: whole file (1,$, no hashes)

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|abcd|s/foo/bar/g'

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

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

# Append multiline text (terminated by a single dot)
exhash file.txt '12|abcd|a' <<'EOF'
new line 1
new line 2
.
EOF

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

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

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

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

# Create a missing file by treating it as empty input
exhash new.txt '0|0000|a' <<'EOF'
first line
.
EOF

Substitute uses Rust regex syntax:

• Pattern syntax is from regex
• Replacement syntax is from regex::Replacer, e.g. $1, $0, ${name}
• \/ 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

When passing multiple commands, each command's lnhashes are verified immediately before that command runs.

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.\n" | exhash file.txt "2|beef|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|0000|a can create a new file.

Stdin filter mode

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

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

Python API

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

Viewing

text = "foo\nbar\n"
view = lnhashview(text)                        # ["1|a1b2|foo", "2|c3d4|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. Commands such as d, m, and sort do not take text.

addr = lnhash(1, "foo")  # "1|a1b2|"
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")])

File helpers

lnhashview_file reads directly from one file path. All file paths, including file-qualified addresses, expand a leading ~ to your home directory. exhash_file(path, cmds, sw=4, inplace=True) uses path as the default file context for unqualified addresses. 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 = exhash_file("file.py", [(addr, "s", "foo", "bar")])

# With inplace=False, files are unchanged and a FileSetEditResult is returned.
res = exhash_file("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 = exhash_file("new.py", [("0|0000|", "a", "print('hi')")])

# File-qualified addresses can edit or transfer lines across files.
cmds = [
    ("src/a.py:24|8f12|,38|c0de|", "m", "src/b.py:$"),
    (r"src/a.py:5|91aa|", "s", r"from \.b import old", r"from \.b import helper"),
]
diff = exhash_file("src/a.py", cmds)

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

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

• res.files: dict of path to FileEditResult
• res.changed: changed paths, in first-touch order
• res.default_path: the default path passed to exhash_file
• res[path]: shorthand for res.files[path]
• res.format_diff(context=1): combined diff with --- path / +++ path headers

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. exhash_cell(path, cell_id, cmds, sw=4, inplace=True) edits one cell; like exhash_file 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|beef|a
new line 1
new line 2

• %%exhash new.py 0|0000| 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|a3f2|,15|b1c3| c replaces just that range, both addresses from one lnhashview_file view.
• One trailing newline (the cell terminator) is stripped; to end the payload with a blank line, leave one extra blank line at the bottom.
• 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)

res.format_diff(context=1) returns a unified-diff-style summary showing only changed lines with context:

res = exhash(text, [(addr, "s", "foo", "baz")])
print(res.format_diff())
# --- original
# +++ modified
# -1|a1b2|foo
# +1|c3d4|baz
#  2|e5f6|bar

All diff strings returned by format_diff, exhash_file, and exhash_cell 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.

Tests

pytest -q