grex is a library as well as a command-line utility that is meant to simplify the often complicated and tedious task of creating regular expressions. It does so by automatically generating regular expressions from user-provided test cases.
This project has started as a Rust port of the JavaScript tool regexgen written by Devon Govett. Although a lot of further useful features could be added to it, its development was apparently ceased several years ago. The plan is now to add these new features to grex as Rust really shines when it comes to command-line tools. grex offers all features that regexgen provides, and more.
The philosophy of this project is to generate the most specific regular expression possible by default which exactly matches the given input only and nothing else. With the use of command-line flags (in the CLI tool) or preprocessing methods (in the library), more generalized expressions can be created.
{min,max} quantifier notation| operator? quantifierPre-compiled 64-Bit binaries are available within the package managers Scoop (for Windows) and Homebrew (for macOS).
scoop install grex
brew tap pemistahl/formulas
brew install grex
Alternatively, you can download the self-contained executable for your platform above and put it in a place of your choice. grex is also hosted on crates.io, the official Rust package registry. If you are a Rust developer and already have the Rust toolchain installed, you can install by compiling from source using cargo, the Rust package manager:
cargo install grex
In order to use grex as a library, simply add it as a dependency to your Cargo.toml file:
toml
[dependencies]
grex = "0.3"
Every generated regular expression is surrounded by the anchors ^ and $ so that it does not accidentally match substrings.
``` $ grex --help grex 0.3.2 Peter M. Stahl pemistahl@gmail.com grex generates regular expressions from user-provided test cases.
USAGE:
grex [FLAGS] ... --file
FLAGS:
-r, --convert-repetitions
Detects repeated non-overlapping substrings and
converts them to {min,max} quantifier notation
-e, --escape
Replaces all non-ASCII characters with unicode escape sequences
--with-surrogates
Converts astral code points to surrogate pairs if --escape is set
-h, --help
Prints help information
-v, --version
Prints version information
OPTIONS:
-f, --file
Reads test cases separated by newline characters from a file
ARGS:
...
One or more test cases separated by blank space
```
Input strings can be read from the command line or from a file. Every file must be encoded as UTF-8 and every input string must be on a separate line:
$ grex -f my-input-file.txt
rust
let regexp = grex::RegExpBuilder::from(&["a", "aa", "aaa"]).build();
assert_eq!(regexp, "^a(aa?)?$");
rust
let regexp = grex::RegExpBuilder::from(&["a", "aa", "aaa"])
.with_converted_repetitions()
.build();
assert_eq!(regexp, "^a{1,3}$");
rust
let regexp = grex::RegExpBuilder::from(&["You smell like 💩."])
.with_escaped_non_ascii_chars(false)
.build();
assert_eq!(regexp, "^You smell like \\u{1f4a9}\\.$");
Old versions of JavaScript do not support unicode escape sequences for the astral code planes (range U+010000 to U+10FFFF). In order to support these symbols in JavaScript regular expressions, the conversion to surrogate pairs is necessary. More information on that matter can be found here.
rust
let regexp = grex::RegExpBuilder::from(&["You smell like 💩."])
.with_escaped_non_ascii_chars(true)
.build();
assert_eq!(regexp, "^You smell like \\u{d83d}\\u{dca9}\\.$");
rust
let regexp = grex::RegExpBuilder::from(&["You smell like 💩💩💩."])
.with_converted_repetitions()
.with_escaped_non_ascii_chars(false)
.build();
assert_eq!(regexp, "^You smel{2} like \\u{1f4a9}{3}\\.$");
The following table showcases what grex can do (using the command-line flags here):
| Input | Output | Note |
| ----- | ------ | ---- |
| a b c | ^[a-c]$ | |
| a c d e f | ^[ac-f]$ | |
| 1 3 4 5 6 | ^[13-6]$ | |
| a b x de | ^(de|[abx])$ | |
| a b bc | ^(bc?|a)$ | |
| a aa aaa | ^a(aa?)?$ | |
| a ab abc | ^a(bc?)?$ | |
| 3.5 4.5 4,5 | ^(3\.5|4[,.]5)$ | |
| [a-z] | ^\[a\-z\]$ | Regex syntax characters are escaped. |
| y̆ a z | ^([az]|y̆)$ | Grapheme y̆ consists of two unicode symbols:U+0079 (Latin Small Letter Y)U+0306 (Combining Breve).
This is why it is not part of
the character class. |
| "I ♥ cake" "I ♥ cookies" | ^I ♥ c(ookies|ake)$ | Input containing blank space must be
surrounded by quotation marks. |
| "I \u{2665} cake" | ^I ♥ cake$ | Unicode escape sequences are converted
back to the original unicode symbol. |
| -r aaa | ^a{3}$ | |
| -r abababa | ^(ab){3}a$ | |
| -r aababab | ^a(ab){3}$ | |
| -r abababaa | ^(ab){3}a{2}$ | |
| -r a aa aaa | ^a{1,3}$ | |
| -r b ba baa baaa | ^b(a{1,3})?$ | |
| -r b ba baa baaaa | ^b(a{1,2}|a{4})?$ | |
| -r xy̆y̆z xy̆y̆y̆z | ^x(y̆){2,3}z$ | The parentheses are needed becausey̆ consists of two unicode symbols. |
| -r xy̆y̆z xy̆y̆y̆y̆z | ^x((y̆){2}|(y̆){4})z$ | |
| -r zyxx yxx | ^z?yx{2}$ | |
| -r 4.5 44.5 44.55 4.55 | ^4{1,2}\.5{1,2}$ | |
| -r "I ♥♥ cake" | ^I ♥{2} cake$ | |
| -r "I \u{2665}\u{2665} cake" | ^I ♥{2} cake$ | |
| -e "I ♥♥ you." | ^I \u{2665}\u{2665} you\.$ | |
| -e -r "I ♥♥ you." | ^I \u{2665}{2} you\.$ | |
| -e "You smell like 💩💩." | ^You smell like \u{1f4a9}\u{1f4a9}\.$ | |
| -e -r "You smell like 💩💩." | ^You smel{2} like \u{1f4a9}{2}\.$ | |
| -e -r --with-surrogates "You smell like 💩💩." | ^You smel{2} like (\u{d83d}\u{dca9}){2}\.$ | For languages such as older
JavaScript versions not supporting
astral codepoints (U+010000 to U+10FFFF),
conversion to surrogate pairs is possible.
More info about this issue can be found here. |
A deterministic finite automaton (DFA) is created from the input strings.
The number of states and transitions between states in the DFA is reduced by applying Hopcroft's DFA minimization algorithm.
The minimized DFA is expressed as a system of linear equations which are solved with Brzozowski's algebraic method, resulting in the final regular expression.
In case you want to contribute something to grex even though it's in a very early stage of development, then I encourage you to do so nevertheless. Do you have ideas for cool features? Or have you found any bugs so far? Feel free to open an issue or send a pull request. It's very much appreciated. :-)