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. mparser-re
  125. naboris
  126. netsnmp
  127. ninja_utils
  128. nx-text
  129. obelisk >= "0.5.0"
  130. ocaml-lsp-server >= "1.9.0"
  131. ocamlformat
  132. ocamlformat-mlx
  133. ocamlformat-rpc < "0.21.0"
  134. ocamlmig
  135. ocgtk
  136. ocp-build
  137. ocp-index
  138. ocsigen-start
  139. ocsigenserver >= "5.1.0"
  140. opam-bin >= "0.9.5" & < "1.1.0"
  141. opam-client
  142. opam-compiler
  143. opam-core
  144. opam-format >= "2.0.8" & != "2.1.0~beta4"
  145. opam-lib
  146. opam-solver >= "2.0.8" & < "2.1.0" | >= "2.2.0"
  147. opam-state >= "2.2.0"
  148. opam_bin_lib
  149. opium
  150. opium_kernel
  151. oranger
  152. orun
  153. ostap
  154. ozulip
  155. pa_ppx_parsetree
  156. pa_ppx_regexp >= "0.04"
  157. pa_ppx_string
  158. parseff
  159. passage >= "0.3.2"
  160. patdiff
  161. pgocaml >= "2.3"
  162. pgx
  163. plato
  164. podge >= "0.3"
  165. ppx_css < "v0.17.0"
  166. ppx_cstubs
  167. ppx_expect < "v0.17.0"
  168. ppx_expect_nobase < "v0.17.3.0"
  169. ppx_mikmatch
  170. ppx_minidebug >= "1.6.0"
  171. ppx_regexp >= "0.3.2"
  172. ppx_test
  173. ppx_tyre
  174. ppxlib >= "0.21.1"
  175. prometheus >= "0.2"
  176. prometheus-app
  177. pyml_bindgen >= "0.3.1"
  178. raga
  179. rdf
  180. re_parser
  181. redis
  182. regrade
  183. rfc1951 < "1.0.0"
  184. safemoney >= "0.3.0"
  185. saga
  186. sarek
  187. sarif >= "0.2.1"
  188. satyrographos
  189. semantic_version
  190. sexp_pretty
  191. shakuhachi
  192. simple-diff
  193. slug
  194. smtml >= "0.21.0"
  195. snf_mcp
  196. soupault
  197. spectrum >= "0.7.0"
  198. spectrum_capabilities
  199. spectrum_palette_ppx
  200. spectrum_tools
  201. spoc
  202. statocaml_profile
  203. stem
  204. swagger
  205. talon < "1.0.0~alpha3"
  206. testcontainers
  207. testo
  208. testo-lwt
  209. testo-util
  210. tezt
  211. timere-parse
  212. touist >= "3.5.0"
  213. tyre >= "0.4"
  214. tyxml >= "4.2.0"
  215. tyxml-syntax
  216. uri < "4.0.0"
  217. uri-re
  218. user-agent-parser
  219. user-setup
  220. uuuu < "0.4.0"
  221. validate
  222. vendredi
  223. wasm_of_ocaml-compiler
  224. webmachine
  225. wire
  226. xtmpl >= "0.18.0"

Conflicts

None