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

Conflicts

None