| re | Python Regular Expressions Source Code |
| re | Reason Module |
| reb | REBOL Source Code |
| red | XRK Redcode Source Code |
| regmap | Altera Quartus II Register Map Information |
| rei | Reason Module Interface |
| rel | Retrieve 4GL Dataset |
| reloc | Windows PE Relocation Section |
| rep | WinDev HyperFileSQL REP File |
| res | Windows Resource File |
| resjson | Microsoft Edge JavaScript Resources Data |
| resources | Visual Studio .NET Resources Data |
| resx | ASP.NET Resource |
| rexx | IBM REXX Source Code |
| rgs | Windows Registration Script |
| rgss2a | RPG Maker VX RGSS Encrypted Archive |
| rgss3a | RPG Maker VX RGSS Encrypted Archive |
| rgssad | RPG Maker VX RGSS Encrypted Archive |
| rh | Borland C++ Resource Header |
| rhistory | R History Data |
| rho | Rholang Source Code |
| rhtml | eRuby HTML Web Page |
| rhtml | Erubis Script |
| ridl | Restricted Interface Definition Language Data |
| rin | Retrieve 4GL Database Index |
| riot | Apache Jena Riotcmd Parser Data |
| rise | RISE Editor Model |
| rjs | Ruby Javascript |
| rkt | Racket Source Code |
| rlib | Rust Compiled Library |
| rll | Microsoft Resource Library |
| rln | Alpha Four Field Rules |
| rlz | CA-Realizer Source Code |
| rmd | R Markdown Source Code |
| rmk | Clipper RMake File |