package re

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  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. doi2bib
  66. dose3
  67. dune-glob >= "3.21.0"
  68. dune-release >= "0.2.0"
  69. dunolint >= "0.0.20251006"
  70. dunolint-lib
  71. dunolint-lib-base
  72. duppy >= "0.9.5"
  73. elpi
  74. expect >= "0.1.0"
  75. expect_test_helpers_core
  76. expect_test_helpers_kernel
  77. ez_file
  78. ez_search
  79. fat-filesystem
  80. git-split < "1.0.0"
  81. gpiod
  82. graphql_parser >= "0.11.0"
  83. hardcaml_verify
  84. hardcaml_waveterm
  85. hardcaml_xilinx_components
  86. hlarp >= "0.0.3"
  87. humane-re
  88. icalendar
  89. index
  90. index-bench
  91. irmin-bench
  92. jingoo >= "1.2.21"
  93. js_of_ocaml >= "3.10.0"
  94. js_of_ocaml-compiler >= "3.10.0"
  95. js_of_ocaml-lwt >= "3.10.0"
  96. js_of_ocaml-ocamlbuild >= "3.10.0" & < "5.0"
  97. js_of_ocaml-ppx >= "3.10.0"
  98. js_of_ocaml-ppx_deriving_json >= "3.10.0"
  99. js_of_ocaml-toplevel >= "3.10.0"
  100. js_of_ocaml-tyxml >= "3.10.0"
  101. jsonschema
  102. jsonschema-core
  103. jsonschema-validation
  104. jwt
  105. jwto
  106. kappa-library
  107. kubecaml
  108. lastfm >= "0.3.4"
  109. ldap >= "2.5.1"
  110. learn-ocaml
  111. ledes
  112. lipsum
  113. liquidsoap >= "2.3.3" & < "2.4.2"
  114. liquidsoap-core >= "2.3.0"
  115. liquidsoap-lang >= "2.3.0"
  116. lwt_ppx_to_let_syntax
  117. MlFront_Cli >= "2.1.4~prerel2" & < "2.3.1"
  118. MlFront_Core >= "2.4.2.30"
  119. MlFront_ZipFile
  120. magic-trace
  121. mdx
  122. mehari
  123. menhir-lsp >= "0.1.2"
  124. mnet-cli >= "0.0.3"
  125. mparser-re
  126. naboris
  127. netsnmp
  128. ninja_utils
  129. nx-text
  130. obelisk >= "0.5.0"
  131. ocaml-lsp-server >= "1.9.0"
  132. ocamlformat
  133. ocamlformat-mlx
  134. ocamlformat-rpc < "0.21.0"
  135. ocamlmig
  136. ocgtk
  137. ocp-build
  138. ocp-index
  139. ocsigen-start
  140. ocsigenserver >= "5.1.0"
  141. opam-bin >= "0.9.5" & < "1.1.0"
  142. opam-client
  143. opam-compiler
  144. opam-core
  145. opam-format >= "2.0.8" & != "2.1.0~beta4"
  146. opam-lib
  147. opam-solver >= "2.0.8" & < "2.1.0" | >= "2.2.0"
  148. opam-state >= "2.2.0"
  149. opam_bin_lib
  150. opium
  151. opium_kernel
  152. oranger
  153. orun
  154. ostap
  155. ozulip
  156. pa_ppx_parsetree
  157. pa_ppx_regexp >= "0.04"
  158. pa_ppx_string
  159. parseff
  160. passage >= "0.3.2"
  161. patdiff
  162. pgocaml >= "2.3"
  163. pgx
  164. plato
  165. podge >= "0.3"
  166. ppx_css < "v0.17.0"
  167. ppx_cstubs
  168. ppx_expect < "v0.17.0"
  169. ppx_expect_nobase < "v0.17.3.0"
  170. ppx_mikmatch
  171. ppx_minidebug >= "1.6.0"
  172. ppx_regexp >= "0.3.2"
  173. ppx_test
  174. ppx_tyre
  175. ppxlib >= "0.21.1"
  176. prometheus >= "0.2"
  177. prometheus-app
  178. pyml_bindgen >= "0.3.1"
  179. raga
  180. rdf
  181. re_parser
  182. redis
  183. regrade
  184. rfc1951 < "1.0.0"
  185. safemoney >= "0.3.0"
  186. saga
  187. sarek
  188. sarif >= "0.2.1"
  189. satyrographos
  190. semantic_version
  191. sexp_pretty
  192. shakuhachi
  193. simple-diff
  194. slug
  195. smtml >= "0.21.0"
  196. snf_mcp
  197. soupault
  198. spectrum >= "0.7.0"
  199. spectrum_capabilities
  200. spectrum_palette_ppx
  201. spectrum_tools
  202. spoc
  203. statocaml_profile
  204. stem
  205. swagger
  206. talon < "1.0.0~alpha3"
  207. testcontainers
  208. testo
  209. testo-lwt
  210. testo-util
  211. tezt
  212. timere-parse
  213. touist >= "3.5.0"
  214. tyre >= "0.4"
  215. tyxml >= "4.2.0"
  216. tyxml-syntax
  217. uri < "4.0.0"
  218. uri-re
  219. user-agent-parser
  220. user-setup
  221. uuuu < "0.4.0"
  222. validate
  223. vendredi
  224. wasm_of_ocaml-compiler
  225. webmachine
  226. wire
  227. xtmpl >= "0.18.0"

Conflicts

None