srgn - a code surgeon

A grep-like tool which understands source code syntax and allows for manipulation in addition to search.

Like grep, regular expressions are a core primitive. Unlike grep, additional capabilities allow for higher precision, with options for manipulation. This allows srgn to operate along dimensions regular expressions and IDE tooling (Rename all, Find all references, ...) alone cannot, complementing them.

srgn is organized around actions to take (if any), acting only within precise, optionally language grammar-aware scopes. In terms of existing tools, think of it as a mix of tr, sed, ripgrep and tree-sitter, with a design goal of simplicity: if you know regex and the basics of the language you are working with, you are good to go.

Quick walkthrough

[!TIP]

All code snippets displayed here are verified as part of unit tests using the actual srgn binary. What is showcased here is guaranteed to work.

The most simple srgn usage works similar to tr:

$ echo 'Hello World!' | srgn '[wW]orld' 'there' # replacement
Hello there!

Matches for the regular expression pattern '[wW]orld' (the scope) are replaced (the action) by the second positional argument. Zero or more actions can be specified:

$ echo 'Hello World!' | srgn '[wW]orld' # zero actions: input returned unchanged
Hello World!
$ echo 'Hello World!' | srgn --upper '[wW]orld' 'you' # two actions: replacement, afterwards uppercasing
Hello YOU!

Replacement is always performed first and specified positionally. Any other actions are applied after and given as command line flags.

Multiple scopes

Similarly, more than one scope can be specified: in addition to the regex pattern, a language grammar-aware scope can be given, which scopes to syntactical elements of source code (think, for example, "all bodies of class definitions in Python"). If both are given, the regular expression pattern is then only applied within that first, language scope. This enables search and manipulation at precision not normally possible using plain regular expressions, and serving a dimension different from tools such as Rename all in IDEs.

For example, consider this (pointless) Python source file:

"""Module for watching birds and their age."""

from dataclasses import dataclass


@dataclass
class Bird:
    """A bird!"""

    name: str
    age: int

    def celebrate_birthday(self):
        print("🎉")
        self.age += 1

    @classmethod
    def from_egg(egg):
        """Create a bird from an egg."""
        pass  # No bird here yet!


def register_bird(bird: Bird, db: Db) -> None:
    assert bird.age >= 0
    with db.tx() as tx:
        tx.insert(bird)

which can be searched using:

$ cat birds.py | srgn --python 'class' 'age'
11:    age: int
15:        self.age += 1

The string age was sought and found only within Python class definitions (and not, for example, in function bodies such as register_bird, where age also occurs and would be nigh impossible to exclude from consideration in vanilla grep). By default, this 'search mode' also prints line numbers. Search mode is entered if no actions are specified, and a language such as --python is given[^3]—think of it like 'ripgrep but with syntactical language elements'.

Searching can also be performed across lines, for example to find methods (aka def within class) lacking docstrings:

$ cat birds.py | srgn --python 'class' 'def .+:\n\s+[^"\s]{3}' # do not try this pattern at home
13:    def celebrate_birthday(self):
14:        print("🎉")

Note how this does not surface either from_egg (has a docstring) or register_bird (not a method, def outside class).

Multiple language scopes

Language scopes themselves can be specified multiple times as well. For example, in the Rust snippet

pub enum Genre {
    Rock(Subgenre),
    Jazz,
}

const MOST_POPULAR_SUBGENRE: Subgenre = Subgenre::Something;

pub struct Musician {
    name: String,
    genres: Vec<Subgenre>,
}

multiple items can be surgically drilled down into as

$ cat music.rs | srgn --rust 'pub-enum' --rust 'type-identifier' 'Subgenre' # AND'ed together
2:    Rock(Subgenre),

where only lines matching all criteria are returned, acting like a logical and between all conditions. Note that conditions are evaluated left-to-right, precluding some combinations from making sense: for example, searching for a Python class body inside of Python doc-strings usually returns nothing. The inverse works as expected however:

$ cat birds.py | srgn --py 'class' --py 'doc-strings' # From earlier example; note `--py` is a shorthand for `--python`
8:    """A bird!"""
19:        """Create a bird from an egg."""

No docstrings outside class bodies are surfaced!

The -j flag changes this behavior: from intersecting left-to-right, to running all queries independently and joining their results, allowing you to search multiple ways at once:

$ cat birds.py | srgn -j --python 'comments' --python 'doc-strings' 'bird[^s]'
8:    """A bird!"""
19:        """Create a bird from an egg."""
20:        pass  # No bird here yet!

The pattern bird[^s] was found inside of comments or docstrings likewise, not just "docstrings within comments".

Working recursively

If standard input is not given, srgn knows how to find relevant source files automatically, for example in this repository:

$ srgn --python 'class' 'age'
docs/samples/birds
11:    age: int
15:        self.age += 1

docs/samples/birds.py
9:    age: int
13:        self.age += 1

It recursively walks its current directory, finding files based on file extensions and shebang lines, processing at very high speed. For example, srgn --go strings '\d+' finds and prints all ~140,000 runs of digits in literal Go strings inside the Kubernetes codebase of ~3,000,000 lines of Go code within 3 seconds on 12 cores of M3. For more on working with many files, see below.

Combining actions and scopes

Scopes and actions can be combined almost arbitrarily (though many combinations are not going to be use- or even meaningful). For example, consider this Python snippet (for examples using other supported languages see below):

"""GNU module."""

def GNU_says_moo():
    """The GNU function -> say moo -> ✅"""

    GNU = """
      GNU
    """  # the GNU...

    print(GNU + " says moo")  # ...says moo

against which the following command is run:

cat gnu.py | srgn --titlecase --python 'doc-strings' '(?<!The )GNU ([a-z]+)' '$1: GNU 🐂 is not Unix'

The anatomy of that invocation is:

• --titlecase (an action) will Titlecase Everything Found In Scope

• --python 'doc-strings' (a scope) will scope to (i.e., only take into consideration) docstrings according to the Python language grammar

• '(?<!The )GNU ([a-z]+)' (a scope) sees only what was already scoped by the previous option, and will narrow it down further. It can never extend the previous scope. The regular expression scope is applied after any language scope(s).

  (?<!) is negative lookbehind syntax, demonstrating how this advanced feature is available. Strings of GNU prefixed by The will not be considered.

• '$1: GNU 🐂 is not Unix' (an action) will replace each matched occurrence (i.e., each input section found to be in scope) with this string. Matched occurrences are patterns of '(?<!The )GNU ([a-z]+)' only within Python docstrings. Notably, this replacement string demonstrates:

  • dynamic variable binding and substitution using $1, which carries the contents captured by the first capturing regex group. That's ([a-z]+), as (?<!The ) is not capturing.
  • full Unicode support (🐂).

The command makes use of multiple scopes (language and regex pattern) and multiple actions (replacement and titlecasing). The result then reads

"""Module: GNU 🐂 Is Not Unix."""

def GNU_says_moo():
    """The GNU function -> say moo -> ✅"""

    GNU = """
      GNU
    """  # the GNU...

    print(GNU + " says moo")  # ...says moo

where the changes are limited to:

- """GNU module."""
+ """Module: GNU 🐂 Is Not Unix."""

def GNU_says_moo():
    """The GNU -> say moo -> ✅"""

[!WARNING]

While srgn is in beta (major version 0), make sure to only (recursively) process files you can safely restore.

Search mode does not overwrite files, so is always safe.

See below for the full help output of the tool.

[!NOTE]

Supported languages are

• C
• C#
• Go
• HCL (Terraform)
• Python
• Rust
• TypeScript

Installation

Prebuilt binaries

Download a prebuilt binary from the releases.

cargo-binstall

This crate provides its binaries in a format compatible with cargo-binstall:

1. Install the Rust toolchain
2. Run cargo install cargo-binstall (might take a while)
3. Run cargo binstall srgn (couple seconds, as it downloads prebuilt binaries from GitHub)

These steps are guaranteed to work™, as they are tested in CI. They also work if no prebuilt binaries are available for your platform, as the tool will fall back to compiling from source.

Homebrew

A formula is available via:

brew install srgn

Nix

Available via unstable:

nix-shell -p srgn

Arch Linux

Available via the AUR.

MacPorts

A port is available:

sudo port install srgn

CI (GitHub Actions)

All GitHub Actions runner images come with cargo preinstalled, and cargo-binstall provides a convenient GitHub Action:

jobs:
  srgn:
    name: Install srgn in CI
    # All three major OSes work
    runs-on: ubuntu-latest
    steps:
      - uses: cargo-bins/cargo-binstall@main
      - name: Install binary
        run: >
          cargo binstall
          --no-confirm
          srgn
      - name: Use binary
        run: srgn --version

The above concludes in just 5 seconds total, as no compilation is required. For more context, see cargo-binstall's advise on CI.

Cargo (compile from source)

1. Install the Rust toolchain
2. A C compiler is required:

   1. On Linux, gcc works.

   2. On macOS, use clang.

   3. On Windows, MSVC works.

      Select "Desktop development with C++" on installation.

3. Run cargo install srgn

Cargo (as a Rust library)

cargo add srgn

See here for more.

Shell completions

Various shells are supported for shell completion scripts. For example, append eval "$(srgn --completions zsh)" to ~/.zshrc for completions in ZSH. An interactive session can then look like:

Walkthrough

The tool is designed around scopes and actions. Scopes narrow down the parts of the input to process. Actions then perform the processing. Generally, both scopes and actions are composable, so more than one of each may be passed. Both are optional (but taking no action is pointless); specifying no scope implies the entire input is in scope.

At the same time, there is considerable overlap with plain tr: the tool is designed to have close correspondence in the most common use cases, and only go beyond when needed.

Actions

The simplest action is replacement. It is specially accessed (as an argument, not an option) for compatibility with tr, and general ergonomics. All other actions are given as flags, or options should they take a value.

Replacement

For example, simple, single-character replacements work as in tr:

$ echo 'Hello, World!' | srgn 'H' 'J'
Jello, World!

The first argument is the scope (literal H in this case). Anything matched by it is subject to processing (replacement by J, the second argument, in this case). However, there is no direct concept of character classes as in tr. Instead, by default, the scope is a regular expression pattern, so its classes can be used to similar effect:

$ echo 'Hello, World!' | srgn '[a-z]' '_'
H____, W____!

The replacement occurs greedily across the entire match by default (note the UTS character class, reminiscent of tr's [:alnum:]):

$ echo 'ghp_oHn0As3cr3T!!' | srgn 'ghp_[[:alnum:]]+' '*' # A GitHub token
*!!

Advanced regex features are supported, for example lookarounds:

$ echo 'ghp_oHn0As3cr3T' | srgn '(?<=ghp_)[[:alnum:]]+' '*'
ghp_*

Take care in using these safely, as advanced patterns come without certain safety and performance guarantees. If they aren't used, performance is not impacted.

The replacement is not limited to a single character. It can be any string, for example to fix this quote:

$ echo '"Using regex, I now have no issues."' | srgn 'no issues' '2 problems'
"Using regex, I now have 2 problems."

The tool is fully Unicode-aware, with useful support for certain advanced character classes:

$ echo 'Mood: 🙂' | srgn '🙂' '😀'
Mood: 😀
$ echo 'Mood: 🤮🤒🤧🦠 :(' | srgn '\p{Emoji_Presentation}' '😷'
Mood: 😷😷😷😷 :(

Variables

Replacements are aware of variables, which are made accessible for use through regex capture groups. Capture groups can be numbered, or optionally named. The zeroth capture group corresponds to the entire match.

$ echo 'Swap It' | srgn '(\w+) (\w+)' '$2 $1' # Regular, numbered
It Swap
$ echo 'Swap It' | srgn '(\w+) (\w+)' '$2 $1$1$1' # Use as many times as you'd like
It SwapSwapSwap
$ echo 'Call +1-206-555-0100!' | srgn 'Call (\+?\d\-\d{3}\-\d{3}\-\d{4}).+' 'The phone number in "$0" is: $1.' # Variable `0` is the entire match
The phone number in "Call +1-206-555-0100!" is: +1-206-555-0100.

A more advanced use case is, for example, code refactoring using named capture groups (perhaps you can come up with a more useful one...):

$ echo 'let x = 3;' | srgn 'let (?<var>[a-z]+) = (?<expr>.+);' 'const $var$var = $expr + $expr;'
const xx = 3 + 3;

As in bash, use curly braces to disambiguate variables from immediately adjacent content:

$ echo '12' | srgn '(\d)(\d)' '$2${1}1'
211
$ echo '12' | srgn '(\d)(\d)' '$2$11' # will fail (`11` is unknown)
$ echo '12' | srgn '(\d)(\d)' '$2${11' # will fail (brace was not closed)

Beyond replacement

Seeing how the replacement is merely a static string, its usefulness is limited. This is where tr's secret sauce ordinarily comes into play: using its character classes, which are valid in the second position as well, neatly translating from members of the first to the second. Here, those classes are instead regexes, and only valid in first position (the scope). A regular expression being a state machine, it is impossible to match onto a 'list of characters', which in tr is the second (optional) argument. That concept is out the window, and its flexibility lost.

Instead, the offered actions, all of them fixed, are used. A peek at the most common use cases for tr reveals that the provided set of actions covers virtually all of them! Feel free to file an issue if your use case is not covered.

Onto the next action.

Deletion

Removes whatever is found from the input. Same flag name as in tr.

$ echo 'Hello, World!' | srgn -d '(H|W|!)'
ello, orld

[!NOTE] As the default scope is to match the entire input, it is an error to specify deletion without a scope.

Squeezing

Squeezes repeats of characters matching the scope into single occurrences. Same flag name as in tr.

$ echo 'Helloooo Woooorld!!!' | srgn -s '(o|!)'
Hello World!

If a character class is passed, all members of that class are squeezed into whatever class member was encountered first:

$ echo 'The number is: 3490834' | srgn -s '\d'
The number is: 3

Greediness in matching is not modified, so take care:

$ echo 'Winter is coming... 🌞🌞🌞' | srgn -s '🌞+'
Winter is coming... 🌞🌞🌞

[!NOTE] The pattern matched the entire run of suns, so there's nothing to squeeze. Summer prevails.

Invert greediness if the use case calls for it:

$ echo 'Winter is coming... 🌞🌞🌞' | srgn -s '🌞+?' '☃️'
Winter is coming... ☃️

[!NOTE] Again, as with deletion, specifying squeezing without an explicit scope is an error. Otherwise, the entire input is squeezed.

Character casing

A good chunk of tr usage falls into this category. It's very straightforward.

$ echo 'Hello, World!' | srgn --lower
hello, world!
$ echo 'Hello, World!' | srgn --upper
HELLO, WORLD!
$ echo 'hello, world!' | srgn --titlecase
Hello, World!

Normalization

Decomposes input according to Normalization Form D, and then discards code points of the Mark category (see examples). That roughly means: take fancy character, rip off dangly bits, throw those away.

$ echo 'Naïve jalapeño ärgert mgła' | srgn -d '\P{ASCII}' # Naive approach
Nave jalapeo rgert mga
$ echo 'Naïve jalapeño ärgert mgła' | srgn --normalize # Normalize is smarter
Naive jalapeno argert mgła

Notice how mgła is out of scope for NFD, as it is "atomic" and thus not decomposable (at least that's what ChatGPT whispers in my ear).

Symbols

This action replaces multi-character, ASCII symbols with appropriate single-code point, native Unicode counterparts.

$ echo '(A --> B) != C --- obviously' | srgn --symbols
(A ⟶ B) ≠ C — obviously

Alternatively, if you're only interested in math, make use of scoping:

$ echo 'A <= B --- More is--obviously--possible' | srgn --symbols '<='
A ≤ B --- More is--obviously--possible

As there is a 1:1 correspondence between an ASCII symbol and its replacement, the effect is reversible[^1]:

$ echo 'A ⇒ B' | srgn --symbols --invert
A => B

There is only a limited set of symbols supported as of right now, but more can be added.

German

This action replaces alternative spellings of German special characters (ae, oe, ue, ss) with their native versions (ä, ö, ü, ß)[^2].

$ echo 'Gruess Gott, Neueroeffnungen, Poeten und Abenteuergruetze!' | srgn --german
Grüß Gott, Neueröffnungen, Poeten und Abenteuergrütze!

This action is based on a word list (compile without german feature if this bloats your binary too much). Note the following features about the above example:

• empty scope and replacement: the entire input will be processed, and no replacement is performed
• Poeten remained as-is, instead of being naively and mistakenly converted to Pöten
• as a (compound) word, Abenteuergrütze is not going to be found in any reasonable word list, but was handled properly nonetheless
• while part of a compound word, Abenteuer remained as-is as well, instead of being incorrectly converted to Abenteür
• lastly, Neueroeffnungen sneakily forms a ue element neither constituent word (neu, Eröffnungen) possesses, but is still processed correctly (despite the mismatched casings as well)

On request, replacements may be forced, as is potentially useful for names:

$ echo 'Frau Loetter steht ueber der Mauer.' | srgn --german-naive '(?<=Frau )\w+'
Frau Lötter steht ueber der Mauer.

Through positive lookahead, nothing but the salutation was scoped and therefore changed. Mauer correctly remained as-is, but ueber was not processed. A second pass fixes this:

$ echo 'Frau Loetter steht ueber der Mauer.' | srgn --german-naive '(?<=Frau )\w+' | srgn --german
Frau Lötter steht über der Mauer.

[!NOTE]

Options and flags pertaining to some "parent" are prefixed with their parent's name, and will imply their parent when given, such that the latter does not need to be passed explicitly. That's why --german-naive is named as it is, and --german needn't be passed.

This behavior might change once clap supports subcommand chaining.

Some branches are undecidable for this modest tool, as it operates without language context. For example, both Busse (busses) and Buße (penance) are legal words. By default, replacements are greedily performed if legal (that's the whole point of srgn, after all), but there's a flag for toggling this behavior:

$ echo 'Busse und Geluebte 🙏' | srgn --german
Buße und Gelübte 🙏
$ echo 'Busse 🚌 und Fussgaenger 🚶‍♀️' | srgn --german-prefer-original
Busse 🚌 und Fußgänger 🚶‍♀️

Combining Actions

Most actions are composable, unless doing so were nonsensical (like for deletion). Their order of application is fixed, so the order of the flags given has no influence (piping multiple runs is an alternative, if needed). Replacements always occur first. Generally, the CLI is designed to prevent misuse and surprises: it prefers crashing to doing something unexpected (which is subjective, of course). Note that lots of combinations are technically possible, but might yield nonsensical results.

Combining actions might look like:

$ echo 'Koeffizienten != Bruecken...' | srgn -Sgu
KOEFFIZIENTEN ≠ BRÜCKEN...

A more narrow scope can be specified, and will apply to all actions equally:

$ echo 'Koeffizienten != Bruecken...' | srgn -Sgu '\b\w{1,8}\b'
Koeffizienten != BRÜCKEN...

The word boundaries are required as otherwise Koeffizienten is matched as Koeffizi and enten. Note how the trailing periods cannot be, for example, squeezed. The required scope of \. would interfere with the given one. Regular piping solves this:

$ echo 'Koeffizienten != Bruecken...' | srgn -Sgu '\b\w{1,8}\b' | srgn -s '\.'
Koeffizienten != BRÜCKEN.

Note: regex escaping (\.) can be circumvent using literal scoping. The specially treated replacement action is also composable:

$ echo 'Mooood: 🤮🤒🤧🦠!!!' | srgn -s '\p{Emoji}' '😷'
Mooood: 😷!!!

Emojis are first all replaced, then squeezed. Notice how nothing else is squeezed.

Scopes

Scopes are the second driving concept to srgn. In the default case, the main scope is a regular expression. The actions section showcased this use case in some detail, so it's not repeated here. It is given as a first positional argument.

Language grammar-aware scopes

srgn extends this through prepared, language grammar-aware scopes, made possible through the excellent tree-sitter library. It offers a queries feature, which works much like pattern matching against a tree data structure.

srgn comes bundled with a handful of the most useful of these queries. Through its discoverable API (either as a library or via CLI, srgn --help), one can learn of the supported languages and available, prepared queries. Each supported language comes with an escape hatch, allowing you to run your own, custom ad-hoc queries. The hatch comes in the form of --lang-query <S EXPRESSION>, where lang is a language such as python. See below for more on this advanced topic.

[!NOTE]

Language scopes are applied first, so whatever regex aka main scope you pass, it operates on each matched language construct individually.

Prepared queries (sample showcases)

This section shows examples for some of the prepared queries.

Finding all unsafe code (Rust)

One advantage of the unsafe keyword in Rust is its "grepability". However, an rg 'unsafe' will of course surface all string matches (rg '\bunsafe\b' helps to an extent), not just those in of the actual Rust language keyword. srgn helps make this more precise. For example:

// Oh no, an unsafe module!
mod scary_unsafe_operations {
    pub unsafe fn unsafe_array_access(arr: &[i32], index: usize) -> i32 {
        // UNSAFE: This function performs unsafe array access without bounds checking
        *arr.get_unchecked(index)
    }

    pub fn call_unsafe_function() {
        let unsafe_numbers = vec![1, 2, 3, 4, 5];
        println!("About to perform an unsafe operation!");
        let result = unsafe {
            // Calling an unsafe function
            unsafe_array_access(&unsafe_numbers, 10)
        };
        println!("Result of unsafe operation: {}", result);
    }
}

can be searched as

$ cat unsafe.rs | srgn --rs 'unsafe' # Note: no 2nd argument necessary
3:    pub unsafe fn unsafe_array_access(arr: &[i32], index: usize) -> i32 {
4:        // UNSAFE: This function performs unsafe array access without bounds checking
5:        *arr.get_unchecked(index)
6:    }
11:        let result = unsafe {
12:            // Calling an unsafe function
13:            unsafe_array_access(&unsafe_numbers, 10)
14:        };

surfacing only truly unsafe items (and not comments, strings etc. merely mentioning it).[^4]

Mass import (module) renaming (Python, Rust)

As part of a large refactor (say, after an acquisition), imagine all imports of a specific package needed renaming:

import math
from pathlib import Path

import good_company.infra
import good_company.aws.auth as aws_auth
from good_company.util.iter import dedupe
from good_company.shopping.cart import *  # Ok but don't do this at home!

good_company = "good_company"  # good_company

At the same time, a move to src/ layout is desired. Achieve this move with:

cat imports.py | srgn --python 'imports' '^good_company' 'src.better_company'

which will yield

import math
from pathlib import Path

import src.better_company.infra
import src.better_company.aws.auth as aws_auth
from src.better_company.util.iter import dedupe
from src.better_company.shopping.cart import *  # Ok but don't do this at home!

good_company = "good_company"  # good_company

Note how the last line remains untouched by this particular operation. To run across many files, see the files option.

Similar import-related edits are supported for other languages as well, for example Rust:

use std::collections::HashMap;

use good_company::infra;
use good_company::aws::auth as aws_auth;
use good_company::util::iter::dedupe;
use good_company::shopping::cart::*;

good_company = "good_company";  // good_company

which, using

cat imports.rs | srgn --rust 'uses' '^good_company' 'better_company'

becomes

use std::collections::HashMap;

use better_company::infra;
use better_company::aws::auth as aws_auth;
use better_company::util::iter::dedupe;
use better_company::shopping::cart::*;

good_company = "good_company";  // good_company

Assigning TODOs (TypeScript)

Perhaps you're using a system of TODO notes in comments:

class TODOApp {
    // TODO app for writing TODO lists
    addTodo(todo: TODO): void {
        // TODO: everything, actually 🤷‍♀️
    }
}

and usually assign people to each note. It's possible to automate assigning yourself to every unassigned note (lucky you!) using

cat todo.ts | srgn --typescript 'comments' 'TODO(?=:)' 'TODO(@poorguy)'

which in this case gives

class TODOApp {
    // TODO app for writing TODO lists
    addTodo(todo: TODO): void {
        // TODO(@poorguy): everything, actually 🤷‍♀️
    }
}

Notice the positive lookahead of (?=:), ensuring an actual TODO note is hit (TODO:). Otherwise, the other TODOs mentioned around the comments would be matched as well.

Converting print calls to proper logging (Python)

Say there's code making liberal use of print:

def print_money():
    """Let's print money 💸."""

    amount = 32
    print("Got here.")

    print_more = lambda s: print(f"Printed {s}")
    print_more(23)  # print the stuff

print_money()
print("Done.")

and a move to logging is desired. That's fully automated by a call of

cat money.py | srgn --python 'function-calls' '^print$' 'logging.info'

yielding

def print_money():
    """Let's print money 💸."""

    amount = 32
    logging.info("Got here.")

    print_more = lambda s: logging.info(f"Printed {s}")
    print_more(23)  # print the stuff

print_money()
logging.info("Done.")

[!NOTE] Note the anchors: print_more is a function call as well, but ^print$ ensures it's not matched.

The regular expression applies after grammar scoping, so operates entirely within the already-scoped context.

Remove all comments (C#)

Overdone, comments can turn into smells. If not tended to, they might very well start lying:

using System.Linq;

public class UserService
{
    private readonly AppDbContext _dbContext;

    /// <summary>
    /// Initializes a new instance of the <see cref="FileService"/> class.
    /// </summary>
    /// <param name="dbContext">The configuration for manipulating text.</param>
    public UserService(AppDbContext dbContext)
    {
        _dbContext /* the logging context */ = dbContext;
    }

    /// <summary>
    /// Uploads a file to the server.
    /// </summary>
    // Method to log users out of the system
    public void DoWork()
    {
        _dbContext.Database.EnsureCreated(); // Ensure the database schema is deleted

        _dbContext.Users.Add(new User /* the car */ { Name = "Alice" });

        /* Begin reading file */
        _dbContext.SaveChanges();

        var user = _dbContext.Users.Where(/* fetch products */ u => u.Name == "Alice").FirstOrDefault();

        /// Delete all records before proceeding
        if (user /* the product */ != null)
        {
            System.Console.WriteLine($"Found user with ID: {user.Id}");
        }
    }
}

So, should you count purging comments among your fetishes, more power to you:

cat UserService.cs | srgn --csharp 'comments' -d '.*' | srgn -d '[[:blank:]]+\n'

The result is a tidy, yet taciturn:

using System.Linq;

public class UserService
{
    private readonly AppDbContext _dbContext;

    public UserService(AppDbContext dbContext)
    {
        _dbContext  = dbContext;
    }

    public void DoWork()
    {
        _dbContext.Database.EnsureCreated();
        _dbContext.Users.Add(new User  { Name = "Alice" });

        _dbContext.SaveChanges();

        var user = _dbContext.Users.Where( u => u.Name == "Alice").FirstOrDefault();

        if (user  != null)
        {
            System.Console.WriteLine($"Found user with ID: {user.Id}");
        }
    }
}

Note how all different sorts of comments were identified and removed. The second pass removes all leftover dangling lines ([:blank:] is tabs and spaces).

[!NOTE] When deleting (-d), for reasons of safety and sanity, a scope is required.

Upgrade VM size (Terraform)

Say you'd like to upgrade the instance size you're using:

data "aws_ec2_instance_type" "tiny" {
  instance_type = "t2.micro"
}

resource "aws_instance" "main" {
  ami           = "ami-022f20bb44daf4c86"
  instance_type = data.aws_ec2_instance_type.tiny.instance_type
}

with

cat ec2.tf | srgn --hcl 'strings' '^t2\.(\w+)$' 't3.$1' | srgn --hcl 'data-names' 'tiny' 'small'

will give

data "aws_ec2_instance_type" "small" {
  instance_type = "t3.micro"
}

resource "aws_instance" "main" {
  ami           = "ami-022f20bb44daf4c86"
  instance_type = data.aws_ec2_instance_type.small.instance_type
}

Rename function (C)

You can rename a function:

void old_function_name(void) {
    ///
    int variable_in_old_function_name;
    ///
}

int main(void) {
    old_function_name();
}

using

cat function.c | srgn --c 'function' 'old_function_name' 'new_function_name'

which will give

void new_function_name(void) {
    ///
    int variable_in_old_function_name;
    ///
}

int main(void) {
    new_function_name();
}

Custom queries

Custom queries allow you to create ad-hoc scopes. These might be useful, for example, to create small, ad-hoc, tailor-made linters, for example to catch code such as:

if x:
    return left
else:
    return right

with an invocation of

cat cond.py | srgn --python-query '(if_statement consequence: (block (return_statement (identifier))) alternative: (else_clause body: (block (return_statement (identifier))))) @cond' --fail-any # will fail

to hint that the code can be more idiomatically rewritten as return left if x else right. Another example, this one in Go, is ensuring sensitive fields are not serialized:

package main

type User struct {
    Name     string `json:"name"`
    Token string `json:"token"`
}

which can be caught as:

cat sensitive.go | srgn --go-query '(field_declaration name: (field_identifier) @name tag: (raw_string_literal) @tag (#match? @name "[tT]oken") (#not-eq? @tag "`json:\"-\"`"))' --fail-any # will fail

Ignoring parts of matches

Occassionally, parts of a match need to be ignored, for example when no suitable tree-sitter node type is available. For example, say we'd like to replace the error with wrong inside the string of the macro body:

fn wrong() {
    let wrong = "wrong";
    error!("This went error");
}

Let's assume there's a node type for matching entire macros (macro_invocation) and one to match macro names (((macro_invocation macro: (identifier) @name))), but none to match macro contents (this is wrong, tree-sitter offers this in the form of token_tree, but let's imagine...). To match just "This went error", the entire macro would need to be matched, with the name part ignored. Any capture name starting with _SRGN_IGNORE will provide just that:

cat wrong.rs | srgn --rust-query '((macro_invocation macro: (identifier) @_SRGN_IGNORE_name) @macro)' 'error' 'wrong'

fn wrong() {
    let wrong = "wrong";
    error!("This went wrong");
}

If it weren't ignored, the result would read wrong!("This went wrong");.

Further reading

These matching expressions are a mouthful. A couple resources exist for getting started with your own queries:

• the official docs on querying

• the great official playground for interactive use, which makes developing queries a breeze. For example, the above Go sample looks like:

  

• How to write a linter using tree-sitter in an hour, a great introduction to the topic in general

• the official tree-sitter CLI

• using srgn with high verbosity (-vvvv) is supposed to grant detailed insights into what's happening to your input, including a representation of the parsed tree

Run against multiple files

Use the --glob option to run against multiple files, in-place. This option accepts a glob pattern. The glob is processed within srgn: it must be quoted to prevent premature shell interpretation. The --glob option takes precedence over the heuristics of language scoping. For example,

$ srgn --go 'comments' --glob 'tests/langs/go/fizz*.go' '\w+'
tests/langs/go/fizzbuzz.go
5:// fizzBuzz prints the numbers from 1 to a specified limit.
6:// For multiples of 3, it prints "Fizz" instead of the number,
7:// for multiples of 5, it prints "Buzz", and for multiples of both 3 and 5,
8:// it prints "FizzBuzz".
25:	// Run the FizzBuzz function for numbers from 1 to 100

finds only what's matched by the (narrow) glob, even though --go queries by themselves would match much more.

srgn will process results fully parallel, using all available threads. For example, 450k lines of Python are processed in about a second, altering over 1000 lines across a couple hundred files:

Run the benchmarks too see performance for your own system.

Explicit failure for (mis)matches

After all scopes are applied, it might turn out no matches were found. The default behavior is to silently succeed:

$ echo 'Some input...' | srgn --delete '\d'
Some input...

The output matches the specification: all digits are removed. There just happened to be none. No matter how many actions are applied, the input is returned unprocessed once this situation is detected. Hence, no unnecessary work is done.

One might prefer receiving explicit feedback (exit code other than zero) on failure:

echo 'Some input...' | srgn --delete --fail-none '\d'  # will fail

The inverse scenario is also supported: failing if anything matched. This is useful for checks (for example, in CI) against "undesirable" content. This works much like a custom, ad-hoc linter.

Take for example "old-style" Python code, where type hints are not yet surfaced to the syntax-level:

def square(a):
    """Squares a number.

    :param a: The number (type: int or float)
    """

    return a**2

This style can be checked against and "forbidden" using:

cat oldtyping.py | srgn --python 'doc-strings' --fail-any 'param.+type'  # will fail

Literal scope

This causes whatever was passed as the regex scope to be interpreted literally. Useful for scopes containing lots of special characters that otherwise would need to be escaped:

$ echo 'stuff...' | srgn -d --literal-string '.'
stuff

Help output

For reference, the full help output with all available options is given below. As with all other snippets, the output is validated for correctness as part of unit tests. Checkout git tags to view help output of specific versions.

$ srgn --help
A grep-like tool which understands source code syntax and allows for manipulation in
addition to search

Usage: srgn [OPTIONS] [SCOPE] [REPLACEMENT]

Arguments:
  [SCOPE]
          Scope to apply to, as a regular expression pattern.
          
          If string literal mode is requested, will be interpreted as a literal
          string.
          
          Actions will apply their transformations within this scope only.
          
          The default is the global scope, matching the entire input. Where that
          default is meaningless or dangerous (e.g., deletion), this argument is
          required.
          
          [default: .*]

Options:
      --completions <SHELL>
          Print shell completions for the given shell.
          
          [possible values: bash, elvish, fish, powershell, zsh]

  -h, --help
          Print help (see a summary with '-h')

  -V, --version
          Print version

Composable Actions:
  -u, --upper
          Uppercase anything in scope.
          
          [env: UPPER=]

  -l, --lower
          Lowercase anything in scope.
          
          [env: LOWER=]

  -t, --titlecase
          Titlecase anything in scope.
          
          [env: TITLECASE=]

  -n, --normalize
          Normalize (Normalization Form D) anything in scope, and throw away marks.
          
          [env: NORMALIZE=]

  -g, --german
          Perform substitutions on German words, such as 'Abenteuergruesse' to
          'Abenteuergrüße', for anything in scope.
          
          ASCII spellings for Umlauts (ae, oe, ue) and Eszett (ss) are replaced by
          their respective native Unicode (ä, ö, ü, ß).
          
          Arbitrary compound words are supported.
          
          Words legally containing alternative spellings are not modified.
          
          Words require correct spelling to be detected.

  -S, --symbols
          Perform substitutions on symbols, such as '!=' to '≠', '->' to '→', on
          anything in scope.
          
          Helps translate 'ASCII art' into native Unicode representations.

  [REPLACEMENT]
          Replace anything in scope with this value.
          
          Variables are supported: if a regex pattern was used for scoping and
          captured content in named or numbered capture groups, access these in the
          replacement value using `$1` etc. for numbered, `$NAME` etc. for named
          capture groups.
          
          This action is specially treated as a positional argument for ergonomics and
          compatibility with `tr`.
          
          If given, will run before any other action.
          
          [env: REPLACE=]

Standalone Actions (only usable alone):
  -d, --delete
          Delete anything in scope.
          
          Cannot be used with any other action: there is no point in deleting and
          performing any other processing. Sibling actions would either receive empty
          input or have their work wiped.

  -s, --squeeze
          Squeeze consecutive occurrences of scope into one.
          
          [env: SQUEEZE=]
          [aliases: squeeze-repeats]

Options (global):
  -G, --glob <GLOB>
          Glob of files to work on (instead of reading stdin).
          
          If actions are applied, they overwrite files in-place.
          
          For supported glob syntax, see:
          <https://docs.rs/glob/0.3.1/glob/struct.Pattern.html>
          
          Names of processed files are written to stdout.

      --fail-no-files
          Fail if working on files (e.g. globbing is requested) but none are found.
          
          Processing no files is not an error condition in itself, but might be an
          unexpected outcome in some contexts. This flag makes the condition explicit.

  -i, --invert
          Undo the effects of passed actions, where applicable.
          
          Requires a 1:1 mapping between replacements and original, which is currently
          available only for:
          
          - symbols: '≠' <-> '!=' etc.
          
          Other actions:
          
          - german: inverting e.g. 'Ä' is ambiguous (can be 'Ae' or 'AE')
          
          - upper, lower, deletion, squeeze: inversion is impossible as information is
            lost
          
          These may still be passed, but will be ignored for inversion and applied
          normally.
          
          [env: INVERT=]

  -L, --literal-string
          Do not interpret the scope as a regex. Instead, interpret it as a literal
          string. Will require a scope to be passed.
          
          [env: LITERAL_STRING=]

      --fail-any
          If anything at all is found to be in scope, fail.
          
          The default is to continue processing normally.

      --fail-none
          If nothing is found to be in scope, fail.
          
          The default is to return the input unchanged (without failure).

  -j, --join-language-scopes
          Join (logical 'OR') multiple language scopes, instead of intersecting them.
          
          The default when multiple language scopes are given is to intersect their
          scopes, left to right. For example, `--go func --go strings` will first
          scope down to `func` bodies, then look for strings only within those. This
          flag instead joins (in the set logic sense) all scopes. The example would
          then scope any `func` bodies, and any strings, anywhere. Language scopers
          can then also be given in any order.
          
          No effect if only a single language scope is given. Also does not affect
          non-language scopers (regex pattern etc.), which always intersect.

  -H, --hidden
          Do not ignore hidden files and directories.

      --gitignored
          Do not ignore `.gitignore`d files and directories.

      --sorted
          Process files in lexicographically sorted order, by file path.
          
          In search mode, this emits results in sorted order. Otherwise, it processes
          files in sorted order.
          
          Sorted processing disables parallel processing.

      --threads <THREADS>
          Number of threads to run processing on, when working with files.
          
          If not specified, will default to available parallelism. Set to 1 for
          sequential, deterministic (but not sorted) output.

  -v, --verbose...
          Increase log verbosity level.
          
          The base log level to use is read from the `RUST_LOG` environment variable
          (if unspecified, defaults to 'error'), and increased according to the number
          of times this flag is given, maxing out at 'trace' verbosity.

Language scopes:
      --c <C>
          Scope C code using a prepared query.
          
          [env: C=]

          Possible values:
          - comments:        Comments (single- and multi-line)
          - strings:         Strings
          - includes:        Includes
          - type-def:        Type definitions
          - enum:            `enum` definitions
          - struct:          `struct` type definitions
          - variable:        Variable definitions
          - function:        All functions usages (declarations and calls)
          - function-def:    Function definitions
          - function-decl:   Function declaration
          - switch:          `switch` blocks
          - if:              `if` blocks
          - for:             `for` blocks
          - while:           `while` blocks
          - do:              `do` blocks
          - union:           `union` blocks
          - identifier:      Identifier
          - declaration:     Declaration
          - call-expression: Call expression

      --c-query <TREE-SITTER-QUERY>
          Scope C code using a custom tree-sitter query.
          
          [env: C_QUERY=]

      --csharp <CSHARP>
          Scope C# code using a prepared query.
          
          [env: CSHARP=]
          [aliases: cs]

          Possible values:
          - comments:             Comments (including XML, inline, doc comments)
          - strings:              Strings (incl. verbatim, interpolated; incl. quotes,
            except for interpolated)
          - usings:               `using` directives (including periods)
          - struct:               `struct` definitions (in their entirety)
          - enum:                 `enum` definitions (in their entirety)
          - interface:            `interface` definitions (in their entirety)
          - class:                `class` definitions (in their entirety)
          - method:               Method definitions (in their entirety)
          - variable-declaration: Variable declarations (in their entirety)
          - property:             Property definitions (in their entirety)
          - constructor:          Constructor definitions (in their entirety)
          - destructor:           Destructor definitions (in their entirety)
          - field:                Field definitions on types (in their entirety)
          - attribute:            Attribute names
          - identifier:           Identifier names

      --csharp-query <TREE-SITTER-QUERY>
          Scope C# code using a custom tree-sitter query.
          
          [env: CSHARP_QUERY=]

      --go <GO>
          Scope Go code using a prepared query.
          
          [env: GO=]

          Possible values:
          - comments:    Comments (single- and multi-line)
          - strings:     Strings (interpreted and raw; excluding struct tags)
          - imports:     Imports
          - type-def:    Type definitions
          - type-alias:  Type alias assignments
          - struct:      `struct` type definitions
          - interface:   `interface` type definitions
          - const:       `const` specifications
          - var:         `var` specifications
          - func:        `func` definitions
          - method:      Method `func` definitions (`func (recv Recv) SomeFunc()`)
          - free-func:   Free `func` definitions (`func SomeFunc()`)
          - init-func:   `func init()` definitions
          - type-params: Type parameters (generics)
          - defer:       `defer` blocks
          - select:      `select` blocks
          - go:          `go` blocks
          - switch:      `switch` blocks
          - labeled:     Labeled statements
          - goto:        `goto` statements
          - struct-tags: Struct tags

      --go-query <TREE-SITTER-QUERY>
          Scope Go code using a custom tree-sitter query.
          
          [env: GO_QUERY=]

      --hcl <HCL>
          Scope HashiCorp Configuration Language code using a prepared query.
          
          [env: HCL=]

          Possible values:
          - variable:       `variable` blocks (in their entirety)
          - resource:       `resource` blocks (in their entirety)
          - data:           `data` blocks (in their entirety)
          - output:         `output` blocks (in their entirety)
          - provider:       `provider` blocks (in their entirety)
          - terraform:      `terraform` blocks (in their entirety)
          - locals:         `locals` blocks (in their entirety)
          - module:         `module` blocks (in their entirety)
          - variables:      Variable declarations and usages
          - resource-names: `resource` name declarations and usages
          - resource-types: `resource` type declarations and usages
          - data-names:     `data` name declarations and usages
          - data-sources:   `data` source declarations and usages
          - comments:       Comments
          - strings:        Literal strings

      --hcl-query <TREE-SITTER-QUERY>
          Scope HashiCorp Configuration Language code using a custom tree-sitter query.
          
          [env: HCL_QUERY=]

      --python <PYTHON>
          Scope Python code using a prepared query.
          
          [env: PYTHON=]
          [aliases: py]

          Possible values:
          - comments:             Comments
          - strings:              Strings (raw, byte, f-strings; interpolation not
            included)
          - imports:              Module names in imports (incl. periods; excl.
            `import`/`from`/`as`/`*`)
          - doc-strings:          Docstrings (not including multi-line strings)
          - function-names:       Function names, at the definition site
          - function-calls:       Function calls
          - class:                Class definitions (in their entirety)
          - def:                  Function definitions (*all* `def` block in their
            entirety)
          - async-def:            Async function definitions (*all* `async def` block in
            their entirety)
          - methods:              Function definitions inside `class` bodies
          - class-methods:        Function definitions decorated as `classmethod` (excl.
            the decorator)
          - static-methods:       Function definitions decorated as `staticmethod` (excl.
            the decorator)
          - with:                 `with` blocks (in their entirety)
          - try:                  `try` blocks (in their entirety)
          - lambda:               `lambda` statements (in their entirety)
          - globals:              Global, i.e. module-level variables
          - variable-identifiers: Identifiers for variables (left-hand side of
            assignments)
          - types:                Types in type hints
          - identifiers:          Identifiers (variable names, ...)

      --python-query <TREE-SITTER-QUERY>
          Scope Python code using a custom tree-sitter query.
          
          [env: PYTHON_QUERY=]

      --rust <RUST>
          Scope Rust code using a prepared query.
          
          [env: RUST=]
          [aliases: rs]

          Possible values:
          - comments:         Comments (line and block styles; excluding doc comments;
            comment chars incl.)
          - doc-comments:     Doc comments (comment chars included)
          - uses:             Use statements (paths only; excl. `use`/`as`/`*`)
          - strings:          Strings (regular, raw, byte; includes interpolation parts in
            format strings!)
          - attribute:        Attributes like `#[attr]`
          - struct:           `struct` definitions
          - priv-struct:      `struct` definitions not marked `pub`
          - pub-struct:       `struct` definitions marked `pub`
          - pub-crate-struct: `struct` definitions marked `pub(crate)`
          - pub-self-struct:  `struct` definitions marked `pub(self)`
          - pub-super-struct: `struct` definitions marked `pub(super)`
          - enum:             `enum` definitions
          - priv-enum:        `enum` definitions not marked `pub`
          - pub-enum:         `enum` definitions marked `pub`
          - pub-crate-enum:   `enum` definitions marked `pub(crate)`
          - pub-self-enum:    `enum` definitions marked `pub(self)`
          - pub-super-enum:   `enum` definitions marked `pub(super)`
          - enum-variant:     Variant members of `enum` definitions
          - fn:               Function definitions
          - impl-fn:          Function definitions inside `impl` blocks (associated
            functions/methods)
          - priv-fn:          Function definitions not marked `pub`
          - pub-fn:           Function definitions marked `pub`
          - pub-crate-fn:     Function definitions marked `pub(crate)`
          - pub-self-fn:      Function definitions marked `pub(self)`
          - pub-super-fn:     Function definitions marked `pub(super)`
          - const-fn:         Function definitions marked `const`
          - async-fn:         Function definitions marked `async`
          - unsafe-fn:        Function definitions marked `unsafe`
          - extern-fn:        Function definitions marked `extern`
          - test-fn:          Function definitions with attributes containing `test`
            (`#[test]`, `#[rstest]`, ...)
          - trait:            `trait` definitions
          - impl:             `impl` blocks
          - impl-type:        `impl` blocks for types (`impl SomeType {}`)
          - impl-trait:       `impl` blocks for traits on types (`impl SomeTrait for
            SomeType {}`)
          - mod:              `mod` blocks
          - mod-tests:        `mod tests` blocks
          - type-def:         Type definitions (`struct`, `enum`, `union`)
          - identifier:       Identifiers
          - type-identifier:  Identifiers for types
          - closure:          Closure definitions
          - unsafe:           `unsafe` keyword usages (`unsafe fn`, `unsafe` blocks,
            `unsafe Trait`, `unsafe impl Trait`)

      --rust-query <TREE-SITTER-QUERY>
          Scope Rust code using a custom tree-sitter query.
          
          [env: RUST_QUERY=]

      --typescript <TYPESCRIPT>
          Scope TypeScript code using a prepared query.
          
          [env: TYPESCRIPT=]
          [aliases: ts]

          Possible values:
          - comments:       Comments
          - strings:        Strings (literal, template)
          - imports:        Imports (module specifiers)
          - function:       Any `function` definitions
          - async-function: `async function` definitions
          - sync-function:  Non-`async function` definitions
          - method:         Method definitions
          - constructor:    `constructor` method definitions
          - class:          `class` definitions
          - enum:           `enum` definitions
          - interface:      `interface` definitions
          - try-catch:      `try`/`catch`/`finally` blocks
          - var-decl:       Variable declarations (`let`, `const`, `var`)
          - let:            `let` variable declarations
          - const:          `const` variable declarations
          - var:            `var` variable declarations
          - type-params:    Type (generic) parameters
          - type-alias:     Type alias declarations
          - namespace:      `namespace` blocks
          - export:         `export` blocks

      --typescript-query <TREE-SITTER-QUERY>
          Scope TypeScript code using a custom tree-sitter query.
          
          [env: TYPESCRIPT_QUERY=]

Options (german):
      --german-prefer-original
          When some original version and its replacement are equally legal, prefer the
          original and do not modify.
          
          For example, "Busse" (original) and "Buße" (replacement) are equally legal
          words: by default, the tool would prefer the latter.
          
          [env: GERMAN_PREFER_ORIGINAL=]

      --german-naive
          Always perform any possible replacement ('ae' -> 'ä', 'ss' -> 'ß', etc.),
          regardless of legality of the resulting word
          
          Useful for names, which are otherwise not modifiable as they do not occur in
          dictionaries. Called 'naive' as this does not perform legal checks.
          
          [env: GERMAN_NAIVE=]

Rust library

While this tool is CLI-first, it is library-very-close-second, and library usage is treated as a first-class citizen just the same. See the library documentation for more, library-specific details.

Note that the binary takes precedence though, which with the crate currently being both a library and binary, creates problems. This might be fixed in the future.

Status and stats

Note: these apply to the entire repository, including the binary.

Code coverage icicle graph

The code is currently structured as (color indicates coverage):

Hover over the rectangles for file names.

Contributing

To see how to build, refer to compiling from source. Otherwise, refer to the guidelines.

Similar tools

An unordered list of similar tools you might be interested in.

• GritQL (very similar)
• ast-grep (very similar)
• Semgrep
• pss
• fastmod
• prefactor
• grep-ast
• amber
• sd
• ripgrep
• ripgrep-structured
• tree-sitter CLI
• tree-sitter-grep
• gron
• Ruleguard (quite different, but useful for custom linting)
• Coccinelle for Rust

Comparison with tr

srgn is inspired by tr, and in its simplest form behaves similarly, but not identically. In theory, tr is quite flexible. In practice, it is commonly used mainly across a couple specific tasks. Next to its two positional arguments ('arrays of characters'), one finds four flags:

1. -c, -C, --complement: complement the first array
2. -d, --delete: delete characters in the first first array
3. -s, --squeeze-repeats: squeeze repeats of characters in the first array
4. -t, --truncate-set1: truncate the first array to the length of the second

In srgn, these are implemented as follows:

1. is not available directly as an option; instead, negation of regular expression classes can be used (e.g., [^a-z]), to much more potent, flexible and well-known effect
2. available (via regex)
3. available (via regex)
4. not available: it's inapplicable to regular expressions, not commonly used and, if used, often misused

To show how uses of tr found in the wild can translate to srgn, consider the following section.

Use cases and equivalences

The following sections are the approximate categories much of tr usage falls into. They were found using GitHub's code search. The corresponding queries are given. Results are from the first page of results at the time. The code samples are links to their respective sources.

As the stdin isn't known (usually dynamic), some representative samples are used and the tool is exercised on those.

Identifier Safety

Making inputs safe for use as identifiers, for example as variable names.

Query

1. tr -C '[:alnum:]_\n' '_'

   Translates to:

   $ echo 'some-variable? 🤔' | srgn '[^[:alnum:]_\n]' '_'
   some_variable___
   

   Similar examples are:

   • tr -C "[:alnum:]" '-'
   • tr -C "A-Za-z0-9" "_"
   • tr -c '[a-zA-Z0-9-]' '-'
   • tr -C 'a-zA-Z0-9@_' '_'

2. tr -c '[:alnum:]' _

   Translates to:

   $ echo 'some  variablê' | srgn '[^[:alnum:]]' '_'
   some__variabl_
   

3. tr -c -s '[:alnum:]' '-'

   Translates to:

   $ echo '🙂 hellö???' | srgn -s '[^[:alnum:]]' '-'
   -hell-
   

Literal-to-literal translation

Translates a single, literal character to another, for example to clean newlines.

Query

1. tr " " ";"

   Translates to:

   $ echo 'x86_64 arm64 i386' | srgn ' ' ';'
   x86_64;arm64;i386
   

   Similar examples are:

   • tr ' ' '-'
   • tr '-' '_'

2. tr '.' "\n":

   Translates to:

   $ echo '3.12.1' | srgn --literal-string '.' '\n'  # Escape sequence works
   3
   12
   1
   $ echo '3.12.1' | srgn '\.' '\n'  # Escape regex otherwise
   3
   12
   1
   

3. tr '\n' ','

   Translates to:

   $ echo -ne 'Some\nMulti\nLine\nText' | srgn --literal-string '\n' ','
   Some,Multi,Line,Text
   

   If escape sequences remain uninterpreted (echo -E, the default), the scope's escape sequence will need to be turned into a literal \ and n as well, as it is otherwise interpreted by the tool as a newline:

   $ echo -nE 'Some\nMulti\nLine\nText' | srgn --literal-string '\\n' ','
   Some,Multi,Line,Text
   

   Similar examples are:

   • tr '\n' ' '
   • tr "\n" " "

Removing a character class

Very useful to remove whole categories in one fell swoop.

Query

1. tr -d '[:punct:]' which they describe as:

   Omit all punctuation characters

   translates to:

   $ echo 'Lots... of... punctuation, man.' | srgn -d '[[:punct:]]'
   Lots of punctuation man
   

Lots of use cases also call for inverting, then removing a character class.

Query

1. tr -cd a-z

   Translates to:

   $ echo 'i RLY love LOWERCASING everything!' | srgn -d '[^[:lower:]]'
   iloveeverything
   

2. tr -cd 'a-zA-Z0-9'

   Translates to:

   $ echo 'All0wed ??? 💥' | srgn -d '[^[:alnum:]]'
   All0wed
   

3. tr -cd '[[:digit:]]'

   Translates to:

   $ echo '{"id": 34987, "name": "Harold"}' | srgn -d '[^[:digit:]]'
   34987
   

Remove literal character(s)

Identical to replacing them with the empty string.

Query

1. tr -d "."

   Translates to:

   $ echo '1632485561.123456' | srgn -d '\.'  # Unix timestamp
   1632485561123456
   

   Similar examples are:

   • tr -d '\'`
   • tr -d ' '
   • tr -d ' '

2. tr -d '\r\n'

   Translates to:

   $ echo -e 'DOS-Style\r\n\r\nLines' | srgn -d '\r\n'
   DOS-StyleLines
   

   Similar examples are:

   • tr -d '\r'
   • tr -d '\r'

Squeeze whitespace

Remove repeated whitespace, as it often occurs when slicing and dicing text.

Query

1. tr -s '[:space:]'

   Translates to:

   $ echo 'Lots   of  space !' | srgn -s '[[:space:]]'  # Single space stays
   Lots of space !
   

   Similar examples are:

   • tr -s " "
   • tr -s [:blank:] (blank is \t and space)
   • tr -s (no argument: this will error out; presumably space was meant)
   • tr -s ' '
   • tr -s ' '
   • tr -s '[:space:]'
   • tr -s ' '

2. tr -s ' ' '\n' (squeeze, then replace)

   Translates to:

   $ echo '1969-12-28    13:37:45Z' | srgn -s ' ' 'T'  # ISO8601
   1969-12-28T13:37:45Z
   

3. tr -s '[:blank:]' ':'

   Translates to:

   $ echo -e '/usr/local/sbin \t /usr/local/bin' | srgn -s '[[:blank:]]' ':'
   /usr/local/sbin:/usr/local/bin
   

Changing character casing

A straightforward use case. Upper- and lowercase are often used.

Query

1. tr A-Z a-z (lowercasing)

   Translates to:

   $ echo 'WHY ARE WE YELLING?' | srgn --lower
   why are we yelling?
   

   Notice the default scope. It can be refined to lowercase only long words, for example:

   $ echo 'WHY ARE WE YELLING?' | srgn --lower '\b\w{,3}\b'
   why are we YELLING?
   

   Similar examples are:

   • tr 'A-Z' 'a-z'
   • tr '[A-Z]' '[a-z]'
   • tr '[A-Z]' '[a-z]'
   • tr '[:upper:]' '[:lower:]'
   • tr "[:upper:]" "[:lower:]"

2. tr '[a-z]' '[A-Z]' (uppercasing)

   Translates to:

   $ echo 'why are we not yelling?' | srgn --upper
   WHY ARE WE NOT YELLING?
   

   Similar examples are:

   • tr '[a-z]' '[A-Z]'
   • tr "[:lower:]" "[:upper:]"
   • tr "[:lower:]" "[:upper:]"

License

This project is licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

[^1]: Currently, reversibility is not possible for any other action. For example, lowercasing is not the inverse of uppercasing. Information is lost, so it cannot be undone. Structure (imagine mixed case) was lost. Something something entropy... [^2]: Why is such a bizzare, unrelated feature included? As usual, historical reasons. The original, core version of srgn was merely a Rust rewrite of a previous, existing tool, which was only concerned with the German feature. srgn then grew from there. [^3]: With zero actions and no language scoping provided, srgn becomes 'useless', and other tools such as ripgrep are much more suitable. That's why an error is emitted and input is returned unchanged. [^4]: Combined with --fail-any, the invocation could be used to fail if any unsafe code is found, like a low-budget linter. In reality, for this case, just use #![forbid(unsafe_code)] though.