repository·main·Indexed 23 days ago
https://github.com/facebookincubator/fastmodA high-performance, interactive find-and-replace tool for large-scale codebase refactoring using regular expressions. Written in Rust, fastmod allows users to review, accept, reject, or edit substitutions match-by-match with colored diffs. It supports multiline regex, file extension filtering, and custom external diff tools.
$EDITOR fallback.fastmod relies on the $EDITOR environment variable for interactive line editing.Since fastmod is written in Rust, you can build it using cargo. Ensure you have a stable Rust toolchain installed.
cargo build --release../target/release/fastmod.$ git clone https://github.com/facebookincubator/fastmod.git
$ cd fastmod
$ cargo build --release
$ ./target/release/fastmod --helpUse fastmod to perform large-scale codebase refactors using regular expressions. The tool is optimized for an interactive workflow where you review changes match-by-match.
Use the -m flag to enter interactive mode. For every match found, fastmod will show a colored diff and prompt you to:
$EDITOR.fastmod uses the Rust regex crate. Note these specific syntax requirements:
${1}, ${2}, etc., in the replacement string instead of Python-style \1 or \2.$$ to represent a literal $ in the replacement string.'...') to prevent your shell (like bash) from interpreting the $ characters before they reach fastmod.You can specify files or directories to process as positional arguments after the regex and substitution strings. You can also limit processing to specific file extensions using the --extensions flag.
# Example: Replacing <font color="..."> with <span style="color: ..."> across a directory
fastmod -m --extensions php,html \
'<font *color="?(.*?)"?>(.*?)</font>' \
'<span style="color: ${1};">${2}</span>' \
/home/jrosenstein/wwwfastmod is using cargo install. If you have built the project from source, you can also install your local build using cargo install.fastmod is a tool designed for large-scale codebase refactors that require human oversight. It uses regular expressions to find and replace text, providing a colored diff and interactive prompts for each match.
Regex Syntax Note:
fastmod uses the Rust regex crate. Unlike Python regexes used in codemod:
${1} instead of \1 to access the first capture group in the replacement string.$$ to write a literal $ in the replacement string.$ characters.fastmod operates in two primary modes based on the --accept-all flag:
Interactive Mode (Default): For each match, fastmod shows a colored diff and prompts the user for action:
y: Accept the change.n: Reject the change.e: Edit the line in the user's $EDITOR.A: Accept this change and all subsequent changes (switches to Fast mode).E: Accept this change and open the editor.q: Quit.Fast Mode (--accept-all): Automatically applies all replacements without prompting. This is significantly faster for large-scale, confident refactors.
By default, fastmod uses a built-in diff viewer. You can specify an external tool to display diffs instead. The tool will be invoked with two temporary file paths as arguments (the old content and the new content).
Examples:
--diff-tool difft
--diff-tool delta
--diff-tool 'difft --color always'The Fastmod struct can be used programmatically to apply patches to files. The method present_and_apply_patches allows you to apply a regex-based replacement to a specific file path.
Note that Fastmod can be initialized with various boolean flags (likely controlling behavior like accepting all, printing changes, etc., though exact constructor signatures depend on the full implementation).
Refer to this list for all available fastmod command-line flags:
| Flag | Long Flag | Description |
|---|---|---|
-m | --multiline | Have regex work over multiple lines (dot matches newlines). |
-d | --dir DIR | The path whose descendant files are to be explored. |
-i | --ignore-case | Perform case-insensitive search. |
-e | --extensions EXT | Comma-delimited list of file extensions to process (e.g., php,html). |
-g | --glob GLOB | Space-delimited list of globs to process. |
--hidden | --hidden | Search hidden files. |
-u | --no-ignore | Also search ignored files (ignores .gitignore, etc.). |
--iglob | --iglob IGLOB | Space-delimited list of case-insensitive globs to process. |
--accept-all | --accept-all | Automatically accept all changes (use with caution). |
--print-changed-files | --print-changed-files | Print the paths of changed files. (Recommended with --accept-all). |
-F | --fixed-strings | Treat REGEX as a literal string. |
--diff-tool | --diff-tool COMMAND | Use an external diff tool (e.g., delta, difftastic). |
Conflicts:
--extensions conflicts with --glob and --iglob.--glob conflicts with --iglob.The fastmod command-line interface accepts a regex to match and a substitution string.
Positional Arguments:
REGEX: The regular expression to match.SUBST: The substitution string to replace matches with.FILE OR DIR: (Optional) Paths whose descendant files are to be explored.Flags:
The fastmod CLI provides several flags to control how replacements are applied and how files are discovered. Key flags include:
--accept-all: Automatically accepts all proposed changes without prompting for user confirmation.--print-changed-files: Prints the paths of all files that were modified during the operation.--dir <PATH>: Specifies the directory in which to search for files.--hidden: Includes hidden files (files starting with a dot on Unix systems) in the search.--no-ignore: Ignores ignore files (like .ignore), ensuring all files in the directory are processed.-F: Used to treat the search string as a fixed string rather than a regular expression.