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. atdcpp
  8. atdd
  9. atdgen >= "2.3.3"
  10. atdgen-runtime = "2.2.1"
  11. atdj >= "2.2.1"
  12. atdpy >= "2.4.1"
  13. atds < "2.3.3"
  14. atdts
  15. aws-config
  16. awsm-codegen
  17. BetterErrors
  18. bancos
  19. bap-byteweight-frontend
  20. bap-callgraph-collator
  21. bap-fsi-benchmark
  22. bap-ida
  23. bap-objdump
  24. bap-print >= "2.2.0"
  25. bap-radare2
  26. benchpress
  27. bibfmt
  28. bio_io >= "0.5.1"
  29. biocaml
  30. bistro < "0.6.0"
  31. bonsai >= "v0.15.0"
  32. caisar >= "4.0"
  33. calculon
  34. calculon-web
  35. caldav
  36. calendar >= "3.0.0"
  37. camlp5 >= "8.02.01"
  38. camlp5-buildscripts
  39. camyll
  40. caqti >= "1.7.0"
  41. catala
  42. chamo
  43. cinaps >= "v0.10.0"
  44. cohttp
  45. coin < "0.1.5"
  46. colibri2
  47. commons
  48. conan >= "0.0.6"
  49. core_bench
  50. core_extended
  51. cosovo
  52. cowabloga >= "0.4.0"
  53. crs
  54. cucumber
  55. cuid
  56. current
  57. current_web
  58. daypack-lib
  59. debian-formats
  60. decompress < "1.0.0"
  61. dns < "4.4.1"
  62. doi2bib
  63. dose3
  64. dune-glob >= "3.21.0"
  65. dune-release >= "0.2.0"
  66. dunolint >= "0.0.20251006"
  67. dunolint-lib
  68. dunolint-lib-base
  69. duppy >= "0.9.5"
  70. elpi
  71. expect >= "0.1.0"
  72. expect_test_helpers_core
  73. expect_test_helpers_kernel
  74. ez_file
  75. ez_search
  76. fat-filesystem
  77. git-split < "1.0.0"
  78. gpiod
  79. graphql_parser >= "0.11.0"
  80. hardcaml_verify
  81. hardcaml_waveterm
  82. hardcaml_xilinx_components
  83. hlarp >= "0.0.3"
  84. horned_worm
  85. humane-re
  86. icalendar
  87. index
  88. index-bench
  89. irmin-bench
  90. jingoo >= "1.2.21"
  91. js_of_ocaml >= "3.10.0"
  92. js_of_ocaml-compiler >= "3.10.0"
  93. js_of_ocaml-lwt >= "3.10.0"
  94. js_of_ocaml-ocamlbuild >= "3.10.0" & < "5.0"
  95. js_of_ocaml-ppx >= "3.10.0"
  96. js_of_ocaml-ppx_deriving_json >= "3.10.0"
  97. js_of_ocaml-toplevel >= "3.10.0"
  98. js_of_ocaml-tyxml >= "3.10.0"
  99. jsonschema
  100. jwt
  101. jwto
  102. kappa-library
  103. kubecaml
  104. labrys
  105. lastfm >= "0.3.4"
  106. ldap >= "2.5.1"
  107. learn-ocaml
  108. ledes
  109. lipsum
  110. liquidsoap >= "2.3.3" & < "2.4.2"
  111. liquidsoap-core >= "2.3.0"
  112. liquidsoap-lang >= "2.3.0"
  113. MlFront_Cli >= "2.1.4~prerel2" & < "2.3.1"
  114. MlFront_Core >= "2.4.2.30"
  115. MlFront_ZipFile
  116. magic-trace
  117. mdx
  118. mehari
  119. menhir-lsp >= "0.1.2"
  120. mparser-re
  121. naboris
  122. netsnmp
  123. ninja_utils
  124. nx-text
  125. obelisk >= "0.5.0"
  126. ocaml-lsp-server >= "1.9.0"
  127. ocamlformat >= "0.11.0"
  128. ocamlformat-mlx
  129. ocamlformat-rpc < "0.21.0"
  130. ocamlmig
  131. ocp-build
  132. ocp-index
  133. ocsigen-start
  134. ocsigenserver >= "5.1.0"
  135. opam-bin >= "0.9.5" & < "1.1.0"
  136. opam-client
  137. opam-compiler
  138. opam-core
  139. opam-format >= "2.0.8" & != "2.1.0~beta4"
  140. opam-lib
  141. opam-solver >= "2.0.8" & < "2.1.0" | >= "2.2.0"
  142. opam-state >= "2.2.0"
  143. opam_bin_lib
  144. opium
  145. opium_kernel
  146. oranger
  147. orun
  148. ostap
  149. ozulip
  150. pa_ppx_parsetree
  151. pa_ppx_regexp >= "0.04"
  152. pa_ppx_string
  153. passage >= "0.3.2"
  154. patdiff
  155. pgocaml >= "2.3"
  156. pgx
  157. plato
  158. podge >= "0.3"
  159. ppx_css < "v0.17.0"
  160. ppx_cstubs
  161. ppx_expect < "v0.17.0"
  162. ppx_expect_nobase < "v0.17.3.0"
  163. ppx_minidebug >= "1.6.0"
  164. ppx_regexp >= "0.3.2"
  165. ppx_test
  166. ppx_tyre
  167. ppxlib >= "0.21.1"
  168. prometheus >= "0.2"
  169. prometheus-app
  170. pyml_bindgen >= "0.3.1"
  171. raga
  172. rdf >= "0.12.0"
  173. re_parser
  174. redis
  175. regenerate
  176. regrade
  177. rfc1951 < "1.0.0"
  178. safemoney >= "0.3.0"
  179. saga
  180. sarek
  181. sarif >= "0.2.1"
  182. satyrographos >= "0.0.2.7"
  183. semantic_version
  184. sexp_pretty
  185. shakuhachi
  186. simple-diff
  187. slug
  188. smtml >= "0.21.0"
  189. snf_mcp
  190. soupault
  191. spoc
  192. statocaml_profile
  193. swagger
  194. talon
  195. testo
  196. testo-lwt
  197. testo-util
  198. tezt
  199. timere-parse
  200. touist >= "3.5.0"
  201. tyre >= "0.4"
  202. tyxml >= "4.2.0"
  203. tyxml-syntax
  204. uri < "4.0.0"
  205. uri-re
  206. user-agent-parser
  207. user-setup
  208. uuuu < "0.4.0"
  209. validate
  210. vendredi
  211. wasm_of_ocaml-compiler
  212. webmachine
  213. xtmpl >= "0.18.0"

Conflicts

None