# flex

> free software alternative to lex

**Wikidata**: [Q1050437](https://www.wikidata.org/wiki/Q1050437)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Flex_(lexical_analyzer_generator))  
**Source**: https://4ort.xyz/entity/flex

## Summary
Flex is a free software alternative to lex, a lexical analyzer generator. It was created by Vern Paxson in 1987 and is used for generating lexical analyzers (scanners) that recognize lexical patterns in text.

## Key Facts
- Flex was created by Vern Paxson in 1987
- It is a free software alternative to lex
- The current stable version is 2.6.4 (released May 6, 2017)
- Flex is licensed under BSD licenses
- It is implemented in C and runs on BSD, GNU/Hurd, and other operating systems
- Flex is available in multiple languages including English, Czech, French, Italian, Korean, Norwegian, Polish, Russian, Serbian, and Persian
- The software is hosted on GitHub at https://github.com/westes/flex
- Flex is packaged for major Linux distributions including Debian, Ubuntu, Fedora, and Arch Linux

## FAQs
### Q: What is flex used for?
A: Flex is used to generate lexical analyzers (scanners) that recognize lexical patterns in text. It's commonly used in compilers and other programs that need to process structured text.

### Q: Who created flex and when?
A: Flex was created by Vern Paxson in 1987 as a free software alternative to the proprietary lex tool.

### Q: What license is flex distributed under?
A: Flex is distributed under BSD licenses, making it free software that can be freely used, modified, and distributed.

## Why It Matters
Flex plays a crucial role in the software development ecosystem as a foundational tool for building compilers, interpreters, and other text-processing applications. As a free software alternative to the proprietary lex tool, it democratized access to lexical analysis capabilities, allowing developers worldwide to build sophisticated text-processing tools without licensing constraints. Its compatibility with lex ensures that existing lex-based codebases can transition to or adopt flex without significant modifications. The tool's continued development and maintenance, with versions up to 2.6.4 as of 2017, demonstrates its enduring relevance in modern software development. Flex's integration into major operating systems and package repositories makes it readily available to developers, contributing to its widespread adoption and the advancement of open-source software development practices.

## Notable For
- Being a free software alternative to the proprietary lex tool
- Maintaining backward compatibility with lex while adding improvements
- Being actively developed since 1987 with regular stable releases
- Wide adoption across major operating systems and Linux distributions
- Support for multiple languages and platforms, making it a versatile tool for developers worldwide

## Body
### Development and History
Flex was created by Vern Paxson in 1987 as a free software alternative to lex, which was originally developed by Mike Lesk at Bell Labs. The tool was designed to be compatible with lex while providing additional features and improvements. Over the years, flex has undergone numerous updates and improvements, with the current stable version being 2.6.4 released in May 2017.

### Technical Implementation
Flex is implemented in C and generates C code that can be compiled and linked with other programs. It uses regular expressions to define lexical patterns and generates scanners that can recognize these patterns in input text. The tool includes features like support for multiple input buffers, start conditions for context-sensitive scanning, and the ability to generate both C and C++ scanners.

### Licensing and Distribution
Flex is distributed under BSD licenses, which are permissive free software licenses. This allows users to freely use, modify, and distribute the software, including in proprietary applications. The tool is available through various package managers and repositories, including GitHub, where the source code is maintained.

### Platform Support
Flex runs on multiple operating systems including BSD variants, GNU/Hurd, and other Unix-like systems. It's packaged for major Linux distributions such as Debian, Ubuntu, Fedora, and Arch Linux, making it easily accessible to developers across different platforms.

### Community and Maintenance
The flex project is actively maintained with contributions from the open-source community. Development continues on GitHub, with the project having a significant presence on SourceForge as well. The tool's documentation is available in multiple languages, reflecting its global user base.

## Schema Markup
```json
{
  "@context": "https://schema.org",
  "@type": "SoftwareApplication",
  "name": "flex",
  "description": "Free software alternative to lex, a lexical analyzer generator",
  "url": "https://github.com/westes/flex",
  "applicationCategory": "DeveloperApplication",
  "creator": {
    "@type": "Person",
    "name": "Vern Paxson"
  },
  "license": "BSD licenses",
  "operatingSystem": ["BSD", "GNU/Hurd", "Linux"],
  "version": "2.6.4",
  "sameAs": [
    "https://en.wikipedia.org/wiki/Flex_(lexical_analyser_generator)",
    "https://www.wikidata.org/wiki/Q1055302"
  ]
}

## References

1. [Source](https://cvsweb.openbsd.org/src/usr.bin/lex/README)
2. [Source](https://cvsweb.openbsd.org/src/usr.bin/lex/parse.y)
3. [Source](https://cvsweb.openbsd.org/src/usr.bin/lex/COPYING)
4. [Source](http://openbsd.su/src/usr.bin/lex/Makefile)
5. Free Software Directory
6. [Release 2.5.39. 2020](https://github.com/westes/flex/releases/tag/flex-2.5.39)
7. [Release 2.6.0. 2016](https://github.com/westes/flex/releases/tag/v2.6.0)
8. [Source](https://sourceforge.net/p/flex/mailman/message/34913710/)
9. [Release 2.6.1. 2016](https://github.com/westes/flex/releases/tag/v2.6.1)
10. [Release 2.6.4. 2017](https://github.com/westes/flex/releases/tag/v2.6.4)
11. [lex 2.6.4 released. 2017](https://sourceforge.net/p/flex/mailman/message/35825789/)
12. [Release 2.6.3. 2016](https://github.com/westes/flex/releases/tag/v2.6.3)
13. [flex v2.6.3 released. 2016](https://sourceforge.net/p/flex/mailman/message/35576910/)
14. [Release 2.6.2. 2016](https://github.com/westes/flex/releases/tag/v2.6.2)
15. Freebase Data Dumps. 2013
16. [flex 2.6.4](https://guix.gnu.org/packages/flex-2.6.4/)