✨ NEW: v2.0.0 is out, refreshed for Python 3.10-3.14 and agent use! It's self-documenting so tell Claude Code to run uvx repren@latest --help and install as a skill.✨

repren is a powerful CLI string replacement and file renaming tool for use by agents or humans for almost any search-and-replace or renaming task.

It is small, self-contained, self-documenting, and works on Python 3.10-3.14 with zero dependencies. Essentially, it is a general-purpose, brute-force text file refactoring tool.

For example, repren could rename occurrences of certain names in a set of source files, while simultaneously renaming the files and directories according to the same pattern and handling all case variations.

It’s more powerful than classic options like perl -pie, rpl, or sed:

• Replacements: It allows rewriting file contents according to one or more literal or regular expression patterns.

• Renames: It can also apply the patterns to rename or move files according to replacements on their full paths, creating directories as needed.

• Regexes: It supports fully expressive regular expressions substitutions, including matching groups for back substitutions (like \1, \2, etc.).

• Simultaneous renames: It performs simultaneous renamings: you can make as many replacements as you want and you can rename “foo” as “bar”, and “bar” as “foo” at once, without requiring a temporary intermediate rename.

• Good hygiene: It is careful: it has a nondestructive “dry run” mode and prints clear stats on its changes. It leaves backups. File operations are done atomically, so interruptions never leave a previously existing file truncated or partly edited.

• Case preserving options: It supports “magic” case-preserving renames that let you find and rename identifiers with case variants (lowerCamel, UpperCamel, lower_underscore, and UPPER_UNDERSCORE) consistently.

• Dry run, backups, and undo: It has convenient options for dry run, undo (restoring backups), and cleanup (deleting backups).

• Text or JSON output: It supports human-readable text output (default) or machine-parseable JSON output (--format=json) for easy integration with scripts and agents.

• Self-documenting: It is packaged with its own nice documentation! Run repren --docs for full documentation.

If file paths are provided, repren replaces those files in place, leaving a backup with extension “.orig” (controlled by the --backup-suffix option).

If directory paths are provided, it applies replacements recursively to all files in the supplied paths that are not in the exclude pattern. If no arguments are supplied, it reads from stdin and writes to stdout.

Patterns can be supplied in a text file, with one or more replacements consisting of regular expression and replacement. For example:

# Sample pattern file
frobinator<tab>glurp
WhizzleStick<tab>AcmeExtrudedPlasticFunProvider
figure ([0-9+])<tab>Figure \1

(Where <tab> is an actual tab character.) Each line is a replacement. Empty lines and #-prefixed comments are ignored.

As a short-cut, a single replacement can be specified on the command line using --from (match) and --to (replacement).

Examples:

# Here `patfile` is a patterns file.
# Rewrite stdin:
repren --patterns=patfile < input > output

# Shortcut with a single pattern replacement (replace foo with bar):
repren --from=foo --to=bar < input > output

# Rewrite a few files in place, also requiring matches be on word breaks:
repren --patterns=patfile --word-breaks myfile1 myfile2 myfile3

# Rewrite whole directory trees. Since this is a big operation, we use
# `-n` to do a dry run that only prints what would be done:
repren -n --patterns=patfile --word-breaks --full mydir1

# Now actually do it:
repren --patterns=patfile --word-breaks --full mydir1

# Same as above, for all case variants:
repren --patterns=patfile --word-breaks --preserve-case --full mydir1

# Same as above but including only .py files and excluding the tests directory
# and any files or directories starting with test_:
repren --patterns=patfile --word-breaks --preserve-case --full --include='.*[.]py$' --exclude='tests|test_.*' mydir1

Run repren --docs for full usage and flags.

If file paths are provided, repren replaces those files in place, leaving a backup with extension “.orig”. If directory paths are provided, it applies replacements recursively to all files in the supplied paths that are not in the exclude pattern. If no arguments are supplied, it reads from stdin and writes to stdout.

There are many tools for search/replace and refactoring. Here’s how repren compares:

When to use each:

• repren: Bulk renames with file/directory renaming, case preservation, or simultaneous swaps. Works on any text file with full backup/undo support.
• sed/awk/perl: Classic approaches for quick one-liners. See classic approaches. Often error-prone for complex patterns and lack dry-run mode, simultaneous swaps, or cross-platform consistency.
• sd: Fast sed replacement (2-11x faster than sed), but limited to simple find/replace without file renaming, case preservation, or multi-pattern swaps.
• fastmod: Good for interactive human review of changes, but lacks case preservation, simultaneous swaps, and file/directory renaming.
• ast-grep: Language-aware refactoring where you need to match code structure (e.g., function calls, not just text). Use when semantic understanding matters more than speed.
• comby: Structural matching across languages without learning AST syntax. Useful when you need to match code patterns like balanced braces, but overkill for simple text refactoring.
• rnr: File/directory renaming only (no content replacement). Has dry-run by default, backup option, and undo via dump files. Use repren if you also need content replacement.

No dependencies except Python 3.10+. It’s easiest to install with uv:

# Install as a tool:
uv tool install repren

# Or run directly without installing:
uvx repren --help

Or, since it’s just one file, you can copy the repren.py script somewhere convenient and make it executable.

repren is ideal for use by AI coding agents (Claude Code, Codex, etc.) since it is powerful, simple to use, and self-documenting. Just tell agents to run uvx repren@latest --help and they have everything they need, including the ability to install it as a skill. Agents can use --format=json for machine-parseable output.

repren includes a built-in skill for Claude Code or other agents.

Install:

# Install globally (available in all projects):
uvx repren --install-skill

# Or install for current project only (shareable via git):
uvx repren --install-skill --agent-base=./.claude

Re-run to update an existing installation.

Manual install: Run uvx repren --skill and save to ~/.claude/skills/repren/SKILL.md (global) or .claude/skills/repren/SKILL.md (project).

Learn more: Claude Code docs and Skills repository.

Let’s try a simple replacement in my working directory (which has a few random source files):

$ repren --from=frobinator-server --to=glurp-server --full --dry-run .
Dry run: No files will be changed
Using 1 patterns:
  'frobinator-server' -> 'glurp-server'
Found 102 files in: .
- modify: ./site.yml: 1 matches
- rename: ./roles/frobinator-server/defaults/main.yml -> ./roles/glurp-server/defaults/main.yml
- rename: ./roles/frobinator-server/files/deploy-frobinator-server.sh -> ./roles/glurp-server/files/deploy-frobinator-server.sh
- rename: ./roles/frobinator-server/files/install-graphviz.sh -> ./roles/glurp-server/files/install-graphviz.sh
- rename: ./roles/frobinator-server/files/frobinator-purge-old-deployments -> ./roles/glurp-server/files/frobinator-purge-old-deployments
- rename: ./roles/frobinator-server/handlers/main.yml -> ./roles/glurp-server/handlers/main.yml
- rename: ./roles/frobinator-server/tasks/main.yml -> ./roles/glurp-server/tasks/main.yml
- rename: ./roles/frobinator-server/templates/frobinator-webservice.conf.j2 -> ./roles/glurp-server/templates/frobinator-webservice.conf.j2
- rename: ./roles/frobinator-server/templates/frobinator-webui.conf.j2 -> ./roles/glurp-server/templates/frobinator-webui.conf.j2
Read 102 files (190382 chars), found 2 matches (0 skipped due to overlaps)
Dry run: Would have changed 2 files, including 0 renames

That was a dry run, so if it looks good, it’s easy to repeat that a second time, dropping the --dry-run flag. If this is in git, we’d do a git diff to verify, test, then commit it all. If we messed up, there are still .orig files present.

Patterns can be supplied using the --from and --to syntax above, but that only works for a single pattern.

In general, you can perform multiple simultaneous replacements by putting them in a patterns file. Each line consists of a regular expression and replacement. For example:

# Sample pattern file
frobinator<tab>glurp
WhizzleStick<tab>AcmeExtrudedPlasticFunProvider
figure ([0-9+])<tab>Figure \1

(Where <tab> is an actual tab character.)

Empty lines and #-prefixed comments are ignored. Capturing groups and back substitutions (such as \1 above) are supported.

# Here `patfile` is a patterns file.
# Rewrite stdin:
repren --patterns=patfile < input > output

# Shortcut with a single pattern replacement (replace foo with bar):
repren --from=foo --to=bar < input > output

# Rewrite a few files in place, also requiring matches be on word breaks:
repren --patterns=patfile --word-breaks myfile1 myfile2 myfile3

# Rewrite whole directory trees. Since this is a big operation, we use
# `-n` to do a dry run that only prints what would be done:
repren -n --patterns=patfile --word-breaks --full mydir1

# Now actually do it:
repren --patterns=patfile --word-breaks --full mydir1

# Same as above, for all case variants:
repren --patterns=patfile --word-breaks --preserve-case --full mydir1

Repren provides tools for managing backup files created during operations:

If you need to revert changes, use --undo with the same patterns as the original operation:

# Original operation:
repren --from=OldClass --to=NewClass --full src/

# Undo the changes:
repren --undo --from=OldClass --to=NewClass --full src/

The undo command:

• Finds all .orig backup files
• Uses the patterns to determine which files were renamed
• Restores the original files and removes renamed files
• Skips with warnings if timestamps look wrong or files are missing

When you’re satisfied with your changes, remove backup files:

# Remove all .orig backup files:
repren --clean-backups src/

# Dry run to see what would be removed:
repren --clean-backups --dry-run src/

# Remove backups with custom suffix:
repren --clean-backups --backup-suffix=.bak src/

A typical workflow:

# 1. Preview changes
repren --dry-run --from=foo --to=bar --full mydir/

# 2. Execute changes (creates .orig backups)
repren --from=foo --to=bar --full mydir/

# 3. Review and test your changes

# 4. Either undo if something went wrong:
repren --undo --from=foo --to=bar --full mydir/

# 4. Or clean up backups when satisfied:
repren --clean-backups mydir/

• All pattern matching is via standard Python regular expressions.

• As with sed, replacements are made line by line by default. Memory permitting, replacements may be done on entire files using --at-once.

• As with sed, replacement text may include backreferences to groups within the regular expression, using the usual syntax: \1, \2, etc.

• In the pattern file, both the regular expression and the replacement may contain the usual escapes \\n, \\t, etc. (To match a multi-line pattern, containing \\n, you must use --at-once.)

• Replacements are all matched on each input file, then all replaced, so it’s possible to swap or otherwise change names in ways that would require multiple steps if done one replacement at a time.

• If two patterns have matches that overlap, only one replacement is applied, with preference to the pattern appearing first in the patterns file.

• If one pattern is a subset of another, consider if --word-breaks will help.

• If patterns have special characters, --literal may help.

• The case-preserving option works by adding all case variants to the pattern replacements, e.g. if the pattern file has foo_bar -> xxx_yyy, the replacements fooBar -> xxxYyy, FooBar -> XxxYyy, FOO_BAR -> XXX_YYY are also made. Assumes each pattern has one casing convention.

• The same logic applies to filenames, with patterns applied to the full file path with slashes replaced and then parent directories created as needed, e.g. my/path/to/filename can be rewritten to my/other/path/to/otherfile. (Use caution and test with -n, especially when using absolute path arguments!)

• Files are never clobbered by renames. If a target already exists, or multiple files are renamed to the same target, numeric suffixes will be added to make the files distinct (".1", “.2”, etc.).

• Files are created at a temporary location, then renamed, so original files are left intact in case of unexpected errors. File permissions are preserved.

• Backups are created of all modified files, with the suffix “.orig”. The suffix can be customized with --backup-suffix.

• By default, recursive searching omits paths starting with “.”. This may be adjusted with --exclude. Files ending in the backup suffix (.orig by default) are always ignored.

• Data is handled as bytes internally, allowing it to work with any encoding or binary files. File contents are not decoded unless necessary (e.g., for logging). However, patterns are specified as strings in the pattern file and command line arguments, and file paths are handled as strings for filesystem operations.

Contributions and issues welcome! Check the output of the test script and if it has changed or needs updating, and commit the clean log changes if you submit a PR.

MIT.