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. atd >= "2.2.1"
  6. atdcpp
  7. atdd
  8. atdgen >= "2.3.3"
  9. atdgen-runtime = "2.2.1"
  10. atdj >= "2.2.1"
  11. atdpy >= "2.4.1"
  12. atds < "2.3.3"
  13. atdts
  14. aws-config
  15. awsm-codegen
  16. BetterErrors
  17. bap-byteweight-frontend
  18. bap-callgraph-collator
  19. bap-fsi-benchmark
  20. bap-ida
  21. bap-objdump
  22. bap-print >= "2.2.0"
  23. bap-radare2
  24. benchpress
  25. bibfmt
  26. bio_io >= "0.5.1"
  27. biocaml
  28. bistro < "0.6.0"
  29. bonsai >= "v0.15.0"
  30. caisar >= "4.0"
  31. calculon
  32. calculon-web
  33. caldav
  34. calendar >= "3.0.0"
  35. camlp5 >= "8.02.01"
  36. camlp5-buildscripts
  37. camyll
  38. caqti >= "1.7.0"
  39. catala
  40. chamo
  41. cinaps >= "v0.10.0"
  42. cohttp
  43. coin
  44. colibri2
  45. commons
  46. conan >= "0.0.6"
  47. core_bench
  48. core_extended
  49. cosovo
  50. cowabloga >= "0.4.0"
  51. crs
  52. cucumber
  53. cuid
  54. current
  55. current_web
  56. daypack-lib
  57. debian-formats
  58. decompress < "1.0.0"
  59. dkml-install-installer >= "0.4.0"
  60. dns < "4.4.1"
  61. doi2bib
  62. dose3
  63. dune-release >= "0.2.0"
  64. dunolint >= "0.0.20251006"
  65. dunolint-lib
  66. dunolint-lib-base
  67. duppy >= "0.9.4"
  68. elpi
  69. expect >= "0.1.0"
  70. expect_test_helpers_core
  71. expect_test_helpers_kernel
  72. ez_file
  73. ez_search
  74. fat-filesystem
  75. git-split < "1.0.0"
  76. gpiod
  77. graphql_parser >= "0.11.0"
  78. hardcaml_verify
  79. hardcaml_waveterm
  80. hardcaml_xilinx_components
  81. hlarp >= "0.0.3"
  82. horned_worm
  83. humane-re
  84. icalendar
  85. index
  86. index-bench
  87. irmin-bench
  88. jingoo >= "1.2.21"
  89. js_of_ocaml >= "3.10.0"
  90. js_of_ocaml-compiler >= "3.10.0"
  91. js_of_ocaml-lwt >= "3.10.0"
  92. js_of_ocaml-ocamlbuild >= "3.10.0" & < "5.0"
  93. js_of_ocaml-ppx >= "3.10.0"
  94. js_of_ocaml-ppx_deriving_json >= "3.10.0"
  95. js_of_ocaml-toplevel >= "3.10.0"
  96. js_of_ocaml-tyxml >= "3.10.0"
  97. jsonschema
  98. jwt
  99. jwto
  100. kappa-library
  101. kubecaml
  102. labrys
  103. lastfm >= "0.3.4"
  104. ldap >= "2.5.1"
  105. learn-ocaml
  106. ledes
  107. lipsum
  108. liquidsoap >= "2.3.3"
  109. liquidsoap-core >= "2.3.0"
  110. liquidsoap-lang >= "2.3.0"
  111. MlFront_Cli >= "2.1.4~prerel2" & < "2.3.1"
  112. MlFront_ZipFile
  113. magic-trace
  114. mdx
  115. mehari
  116. mparser-re
  117. naboris
  118. netsnmp
  119. ninja_utils
  120. nx-text
  121. obelisk >= "0.5.0"
  122. ocaml-lsp-server >= "1.9.0"
  123. ocamlformat >= "0.11.0"
  124. ocamlformat-mlx
  125. ocamlformat-rpc < "0.21.0"
  126. ocamlmig
  127. ocp-build
  128. ocp-index
  129. ocsigen-start
  130. ocsigenserver >= "5.1.0"
  131. octez-bls12-381-signature
  132. octez-libs
  133. opam-bin >= "0.9.5" & < "1.1.0"
  134. opam-client
  135. opam-compiler
  136. opam-core
  137. opam-format >= "2.0.8" & != "2.1.0~beta4"
  138. opam-lib
  139. opam-solver >= "2.0.8" & < "2.1.0" | >= "2.2.0"
  140. opam-state >= "2.2.0"
  141. opam_bin_lib
  142. opium
  143. opium_kernel
  144. oranger
  145. orun
  146. ostap
  147. ozulip
  148. pa_ppx_parsetree
  149. pa_ppx_regexp >= "0.04"
  150. pa_ppx_string
  151. patdiff
  152. pgocaml >= "2.3"
  153. pgx
  154. plato
  155. podge >= "0.3"
  156. ppx_css < "v0.17.0"
  157. ppx_cstubs
  158. ppx_expect < "v0.17.0"
  159. ppx_expect_nobase
  160. ppx_minidebug >= "1.6.0"
  161. ppx_regexp >= "0.3.2"
  162. ppx_test
  163. ppx_tyre
  164. ppxlib >= "0.21.1"
  165. prometheus >= "0.2"
  166. prometheus-app
  167. pyml_bindgen >= "0.3.1"
  168. rdf >= "0.12.0"
  169. re_parser
  170. redis
  171. regenerate
  172. rfc1951 < "1.0.0"
  173. safemoney >= "0.3.0"
  174. saga
  175. sarek
  176. sarif >= "0.2.1"
  177. satyrographos >= "0.0.2.7"
  178. semantic_version
  179. sexp_pretty
  180. simple-diff
  181. slug
  182. snf_mcp
  183. soupault
  184. spoc
  185. statocaml_profile
  186. swagger
  187. talon
  188. testo
  189. testo-lwt
  190. testo-util
  191. tezos-clic >= "16.0"
  192. tezos-stdlib-unix
  193. tezt
  194. timere-parse
  195. touist >= "3.5.0"
  196. tyre >= "0.4"
  197. tyxml >= "4.2.0"
  198. tyxml-syntax
  199. uri < "4.0.0"
  200. uri-re
  201. user-agent-parser
  202. user-setup
  203. uuuu
  204. validate
  205. vendredi
  206. wasm_of_ocaml-compiler
  207. webmachine
  208. xtmpl >= "0.18.0"

Conflicts

None