package re

  1. Overview
  2. Docs
RE is a regular expression library for OCaml

Install 

dune-project
 Dependency

github.com Readme Changelog LGPL-2.1-or-later WITH OCaml-LGPL-linking-exception License Edit opam file Versions (20)

Authors

  1. J
    Jerome Vouillon
  2. T
    Thomas Gazagnaire
  3. A
    Anil Madhavapeddy
  4. R
    Rudi Grinberg
  5. Gabriel Radanne

Maintainers

  1. R
    Rudi Grinberg <me@rgrinberg.com>

Sources

1.14.0.tar.gz
md5=03f4a83100cb9229a796b85c698076e1
sha512=cd2cc39f951ca6b7be631bbb5531ed13bc040e629842671bf6fef3911b20ef1653fa9a1f0aa23b094d252cffc9a9efe7ffca69e50d362ab935bc0cc447548124

Description

Pure OCaml regular expressions with:

  • Perl-style regular expressions (module Re.Perl)
  • Posix extended regular expressions (module Re.Posix)
  • Emacs-style regular expressions (module Re.Emacs)
  • Shell-style file globbing (module Re.Glob)
  • Compatibility layer for OCaml's built-in Str module (module Re.Str)

Published: 22 Sep 2025

README

Description

Re is a regular expression library for OCaml. Build status

Contact

This library has been written by Jerome Vouillon (Jerome.Vouillon@pps.univ-paris-diderot.fr). It can be downloaded from https://github.com/ocaml/ocaml-re

Bug reports, suggestions and contributions are welcome.

Features

The following styles of regular expressions are supported:

  • Perl-style regular expressions (module Re.Perl);
  • Posix extended regular expressions (module Re.Posix);
  • Emacs-style regular expressions (module Re.Emacs);
  • Shell-style file globbing (module Re.Glob).

It is also possible to build regular expressions by combining simpler regular expressions (module Re).

The most notable missing features are back-references and look-ahead/look-behind assertions.

There is also a subset of the PCRE interface available in the Re.Pcre module. This makes it easier to port code from that library to Re with minimal changes.

Performances

The matches are performed by lazily building a DFA (deterministic finite automaton) from the regular expression. As a consequence, matching takes linear time in the length of the matched string.

The compilation of patterns is slower than with libraries using back-tracking, such as PCRE. But, once a large enough part of the DFA is built, matching is extremely fast.

Of course, for some combinations of regular expression and string, the part of the DFA that needs to be build is so large that this point is never reached, and matching will be slow. This is not expected to happen often in practice, and actually a lot of expressions that behaves badly with a backtracking implementation are very efficient with this implementation.

The library is at the moment entirely written in OCaml. As a consequence, regular expression matching is much slower when the library is compiled to bytecode than when it is compiled to native code.

Here are some timing results (Pentium III 500Mhz):

  • Scanning a 1Mb string containing only as, except for the last character which is a b, searching for the pattern aa?b (repeated 100 times):

    • RE: 2.6s
    • PCRE: 68s

  • Regular expression example from http://www.bagley.org/~doug/shootout/ [1]

    • RE: 0.43s
    • PCRE: 3.68s

    [1] this page is no longer up but is available via the Internet Archive http://web.archive.org/web/20010429190941/http://www.bagley.org/~doug/shootout/bench/regexmatch/

  • The large regular expression (about 2000 characters long) that Unison uses with my preference file to decide whether a file should be ignored or not. This expression is matched against a filename about 20000 times.

    • RE: 0.31s
    • PCRE: 3.7s However, RE is only faster than PCRE when there are more than about 300 filenames.

Dependencies (2)

  1. ocaml >= "4.13.0"
  2. dune >= "3.17"

Dev Dependencies (5)

  1. odoc with-doc
  2. conf-npm with-test
  3. js_of_ocaml with-test
  4. ounit2 with-test
  5. ppx_expect with-test

  1. alcotest
  2. alcotest-async
  3. alcotest-lwt
  4. alcotest-mirage
  5. alice
  6. atd >= "2.2.1"
  7. atd-jsonlike
  8. atdcpp
  9. atdd
  10. atdgen >= "2.3.3"
  11. atdgen-runtime = "2.2.1"
  12. atdj >= "2.2.1"
  13. atdpy >= "2.4.1"
  14. atds < "2.3.3"
  15. atdts
  16. aws-config
  17. awsm-codegen
  18. awso
  19. BetterErrors
  20. bancos
  21. bap-byteweight-frontend
  22. bap-callgraph-collator
  23. bap-fsi-benchmark
  24. bap-ida
  25. bap-objdump
  26. bap-print
  27. bap-radare2
  28. bibfmt
  29. bio_io >= "0.5.1"
  30. biocaml
  31. bonsai >= "v0.15.0"
  32. brot
  33. caisar >= "4.0"
  34. calculon
  35. calculon-web
  36. caldav
  37. calendar >= "3.0.0"
  38. camlp5 >= "8.02.01"
  39. camlp5-buildscripts
  40. camyll
  41. caqti >= "1.7.0"
  42. cascade
  43. catala
  44. catala-format >= "1.2.0"
  45. chamo
  46. ciao_lwt
  47. cinaps
  48. cohttp
  49. coin < "0.1.5"
  50. colibri2
  51. commons
  52. conan >= "0.0.6"
  53. core_bench
  54. core_extended
  55. cosovo
  56. cowabloga >= "0.4.0"
  57. crs
  58. cucumber
  59. cuid
  60. current
  61. current_web
  62. daypack-lib
  63. debian-formats
  64. decompress < "1.0.0"
  65. dns < "4.4.1"
  66. docfd >= "13.0.0"
  67. doi2bib
  68. dose3
  69. dune-glob >= "3.21.0"
  70. dune-release >= "0.2.0"
  71. dunolint >= "0.0.20251006"
  72. dunolint-lib
  73. dunolint-lib-base
  74. duppy >= "0.9.5"
  75. elpi
  76. expect >= "0.1.0"
  77. expect_test_helpers_core
  78. expect_test_helpers_kernel
  79. ez_file
  80. ez_search
  81. fat-filesystem
  82. git-split < "1.0.0"
  83. gpiod
  84. graphql_parser >= "0.11.0"
  85. hardcaml_verify
  86. hardcaml_waveterm
  87. hardcaml_xilinx_components
  88. hlarp >= "0.0.3"
  89. humane-re
  90. icalendar
  91. index
  92. index-bench
  93. irmin-bench
  94. jingoo >= "1.2.21"
  95. js_of_ocaml >= "3.10.0"
  96. js_of_ocaml-compiler >= "3.10.0"
  97. js_of_ocaml-lwt >= "3.10.0"
  98. js_of_ocaml-ocamlbuild >= "3.10.0" & < "5.0"
  99. js_of_ocaml-ppx >= "3.10.0"
  100. js_of_ocaml-ppx_deriving_json >= "3.10.0"
  101. js_of_ocaml-toplevel >= "3.10.0"
  102. js_of_ocaml-tyxml >= "3.10.0"
  103. jsonschema
  104. jsonschema-core
  105. jsonschema-validation
  106. jwt
  107. jwto
  108. kappa-library
  109. kubecaml
  110. lastfm >= "0.3.4"
  111. ldap >= "2.5.1"
  112. learn-ocaml
  113. ledes
  114. lipsum
  115. liquidsoap >= "2.3.3" & < "2.4.2"
  116. liquidsoap-core >= "2.3.0"
  117. liquidsoap-lang >= "2.3.0"
  118. lwt_ppx_to_let_syntax
  119. MlFront_Cli >= "2.1.4~prerel2" & < "2.3.1"
  120. MlFront_Core >= "2.4.2.30"
  121. MlFront_ZipFile
  122. magic-trace
  123. mdx
  124. mehari
  125. menhir-lsp >= "0.1.2"
  126. menhirformat
  127. mnet-cli >= "0.0.3"
  128. mparser-re
  129. naboris
  130. netsnmp
  131. ninja_utils
  132. nx-text
  133. obelisk >= "0.5.0"
  134. ocaml-lsp-server >= "1.9.0"
  135. ocamlformat
  136. ocamlformat-mlx
  137. ocamlformat-rpc < "0.21.0"
  138. ocamlmig
  139. ocgtk < "0.1~preview2"
  140. ocp-build
  141. ocp-index
  142. ocsigen-start
  143. ocsigenserver >= "5.1.0"
  144. opam-bin >= "0.9.5" & < "1.1.0"
  145. opam-client
  146. opam-compiler
  147. opam-core
  148. opam-format >= "2.0.8" & != "2.1.0~beta4"
  149. opam-lib
  150. opam-solver >= "2.0.8" & < "2.1.0" | >= "2.2.0"
  151. opam-state >= "2.2.0"
  152. opam_bin_lib
  153. opium
  154. opium_kernel
  155. oranger
  156. orun
  157. ostap
  158. ozulip
  159. pa_ppx_parsetree
  160. pa_ppx_regexp >= "0.04"
  161. pa_ppx_string
  162. parseff
  163. passage >= "0.3.2"
  164. patdiff
  165. pgocaml >= "2.3"
  166. pgx
  167. plato
  168. playwright
  169. podge >= "0.3"
  170. ppx_css < "v0.17.0"
  171. ppx_cstubs
  172. ppx_expect < "v0.17.0"
  173. ppx_expect_nobase = "v0.17.2.2"
  174. ppx_mikmatch
  175. ppx_minidebug >= "1.6.0"
  176. ppx_regexp >= "0.3.2"
  177. ppx_test
  178. ppx_tyre
  179. ppxlib >= "0.21.1"
  180. prometheus >= "0.2"
  181. prometheus-app
  182. pyml_bindgen >= "0.3.1"
  183. raga
  184. rdf
  185. re_parser
  186. redis
  187. regrade
  188. rfc1951 < "1.0.0"
  189. safemoney >= "0.3.0"
  190. saga
  191. sarek
  192. sarif >= "0.2.1"
  193. satyrographos
  194. semantic_version
  195. sexp_pretty
  196. shakuhachi
  197. simple-diff
  198. slug
  199. smtml >= "0.21.0"
  200. snf_mcp
  201. soupault
  202. spectrum >= "0.7.0"
  203. spectrum_capabilities
  204. spectrum_palette_ppx
  205. spectrum_tools
  206. spoc
  207. statocaml_profile
  208. stem
  209. swagger
  210. talon < "1.0.0~alpha3"
  211. testcontainers
  212. testo
  213. testo-lwt
  214. testo-util
  215. tezt
  216. timere-parse
  217. touist >= "3.5.0"
  218. tyre >= "0.4"
  219. tyxml >= "4.2.0"
  220. tyxml-syntax
  221. uri < "4.0.0"
  222. uri-re
  223. user-agent-parser
  224. user-setup
  225. uuuu < "0.4.0"
  226. validate
  227. vendredi
  228. wasm_of_ocaml-compiler
  229. wax-lib
  230. webmachine
  231. wire
  232. xtmpl >= "0.18.0"

Conflicts

None