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. bap-byteweight-frontend
  19. bap-callgraph-collator
  20. bap-fsi-benchmark
  21. bap-ida
  22. bap-objdump
  23. bap-print >= "2.2.0"
  24. bap-radare2
  25. benchpress
  26. bibfmt
  27. bio_io >= "0.5.1"
  28. biocaml
  29. bistro < "0.6.0"
  30. bonsai >= "v0.15.0"
  31. caisar >= "4.0"
  32. calculon
  33. calculon-web
  34. caldav
  35. calendar >= "3.0.0"
  36. camlp5 >= "8.02.01"
  37. camlp5-buildscripts
  38. camyll
  39. caqti >= "1.7.0"
  40. catala
  41. chamo
  42. cinaps >= "v0.10.0"
  43. cohttp
  44. coin < "0.1.5"
  45. colibri2
  46. commons
  47. conan >= "0.0.6"
  48. core_bench
  49. core_extended
  50. cosovo
  51. cowabloga >= "0.4.0"
  52. crs
  53. cucumber
  54. cuid
  55. current
  56. current_web
  57. daypack-lib
  58. debian-formats
  59. decompress < "1.0.0"
  60. dkml-install-installer >= "0.4.0"
  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 >= "0.9.4"
  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"
  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. octez-bls12-381-signature
  136. octez-libs
  137. opam-bin >= "0.9.5" & < "1.1.0"
  138. opam-client
  139. opam-compiler
  140. opam-core
  141. opam-format >= "2.0.8" & != "2.1.0~beta4"
  142. opam-lib
  143. opam-solver >= "2.0.8" & < "2.1.0" | >= "2.2.0"
  144. opam-state >= "2.2.0"
  145. opam_bin_lib
  146. opium
  147. opium_kernel
  148. oranger
  149. orun
  150. ostap
  151. ozulip
  152. pa_ppx_parsetree
  153. pa_ppx_regexp >= "0.04"
  154. pa_ppx_string
  155. passage >= "0.3.2"
  156. patdiff
  157. pgocaml >= "2.3"
  158. pgx
  159. plato
  160. podge >= "0.3"
  161. ppx_css < "v0.17.0"
  162. ppx_cstubs
  163. ppx_expect < "v0.17.0"
  164. ppx_expect_nobase < "v0.17.3.0"
  165. ppx_minidebug >= "1.6.0"
  166. ppx_regexp >= "0.3.2"
  167. ppx_test
  168. ppx_tyre
  169. ppxlib >= "0.21.1"
  170. prometheus >= "0.2"
  171. prometheus-app
  172. pyml_bindgen >= "0.3.1"
  173. raga
  174. rdf >= "0.12.0"
  175. re_parser
  176. redis
  177. regenerate
  178. regrade
  179. rfc1951 < "1.0.0"
  180. safemoney >= "0.3.0"
  181. saga
  182. sarek
  183. sarif >= "0.2.1"
  184. satyrographos >= "0.0.2.7"
  185. semantic_version
  186. sexp_pretty
  187. shakuhachi
  188. simple-diff
  189. slug
  190. snf_mcp
  191. soupault
  192. spoc
  193. statocaml_profile
  194. swagger
  195. talon
  196. testo
  197. testo-lwt
  198. testo-util
  199. tezos-clic >= "16.0"
  200. tezos-stdlib-unix
  201. tezt
  202. timere-parse
  203. touist >= "3.5.0"
  204. tyre >= "0.4"
  205. tyxml >= "4.2.0"
  206. tyxml-syntax
  207. uri < "4.0.0"
  208. uri-re
  209. user-agent-parser
  210. user-setup
  211. uuuu < "0.4.0"
  212. validate
  213. vendredi
  214. wasm_of_ocaml-compiler
  215. webmachine
  216. xtmpl >= "0.18.0"

Conflicts

None