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. BetterErrors
  19. bancos
  20. bap-byteweight-frontend
  21. bap-callgraph-collator
  22. bap-fsi-benchmark
  23. bap-ida
  24. bap-objdump
  25. bap-print
  26. bap-radare2
  27. bibfmt
  28. bio_io >= "0.5.1"
  29. biocaml
  30. bonsai >= "v0.15.0"
  31. brot
  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. ciao_lwt
  44. cinaps
  45. cohttp
  46. coin < "0.1.5"
  47. colibri2
  48. commons
  49. conan >= "0.0.6"
  50. core_bench
  51. core_extended
  52. cosovo
  53. cowabloga >= "0.4.0"
  54. crs
  55. cucumber
  56. cuid
  57. current
  58. current_web
  59. daypack-lib
  60. debian-formats
  61. decompress < "1.0.0"
  62. dns < "4.4.1"
  63. doi2bib
  64. dose3
  65. dune-glob >= "3.21.0"
  66. dune-release >= "0.2.0"
  67. dunolint >= "0.0.20251006"
  68. dunolint-lib
  69. dunolint-lib-base
  70. duppy >= "0.9.5"
  71. elpi
  72. expect >= "0.1.0"
  73. expect_test_helpers_core
  74. expect_test_helpers_kernel
  75. ez_file
  76. ez_search
  77. fat-filesystem
  78. git-split < "1.0.0"
  79. gpiod
  80. graphql_parser >= "0.11.0"
  81. hardcaml_verify
  82. hardcaml_waveterm
  83. hardcaml_xilinx_components
  84. hlarp >= "0.0.3"
  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. jsonschema-core
  101. jsonschema-validation
  102. jwt
  103. jwto
  104. kappa-library
  105. kubecaml
  106. lastfm >= "0.3.4"
  107. ldap >= "2.5.1"
  108. learn-ocaml
  109. ledes
  110. lipsum
  111. liquidsoap >= "2.3.3" & < "2.4.2"
  112. liquidsoap-core >= "2.3.0"
  113. liquidsoap-lang >= "2.3.0"
  114. lwt_ppx_to_let_syntax
  115. MlFront_Cli >= "2.1.4~prerel2" & < "2.3.1"
  116. MlFront_Core >= "2.4.2.30"
  117. MlFront_ZipFile
  118. magic-trace
  119. mdx
  120. mehari
  121. menhir-lsp >= "0.1.2"
  122. mparser-re
  123. naboris
  124. netsnmp
  125. ninja_utils
  126. nx-text
  127. obelisk >= "0.5.0"
  128. ocaml-lsp-server >= "1.9.0"
  129. ocamlformat
  130. ocamlformat-mlx
  131. ocamlformat-rpc < "0.21.0"
  132. ocamlmig
  133. ocgtk
  134. ocp-build
  135. ocp-index
  136. ocsigen-start
  137. ocsigenserver >= "5.1.0"
  138. opam-bin >= "0.9.5" & < "1.1.0"
  139. opam-client
  140. opam-compiler
  141. opam-core
  142. opam-format >= "2.0.8" & != "2.1.0~beta4"
  143. opam-lib
  144. opam-solver >= "2.0.8" & < "2.1.0" | >= "2.2.0"
  145. opam-state >= "2.2.0"
  146. opam_bin_lib
  147. opium
  148. opium_kernel
  149. oranger
  150. orun
  151. ostap
  152. ozulip
  153. pa_ppx_parsetree
  154. pa_ppx_regexp >= "0.04"
  155. pa_ppx_string
  156. parseff
  157. passage >= "0.3.2"
  158. patdiff
  159. pgocaml >= "2.3"
  160. pgx
  161. plato
  162. podge >= "0.3"
  163. ppx_css < "v0.17.0"
  164. ppx_cstubs
  165. ppx_expect < "v0.17.0"
  166. ppx_expect_nobase < "v0.17.3.0"
  167. ppx_mikmatch
  168. ppx_minidebug >= "1.6.0"
  169. ppx_regexp >= "0.3.2"
  170. ppx_test
  171. ppx_tyre
  172. ppxlib >= "0.21.1"
  173. prometheus >= "0.2"
  174. prometheus-app
  175. pyml_bindgen >= "0.3.1"
  176. raga
  177. rdf
  178. re_parser
  179. redis
  180. regrade
  181. rfc1951 < "1.0.0"
  182. safemoney >= "0.3.0"
  183. saga
  184. sarek
  185. sarif >= "0.2.1"
  186. satyrographos
  187. semantic_version
  188. sexp_pretty
  189. shakuhachi
  190. simple-diff
  191. slug
  192. smtml >= "0.21.0"
  193. snf_mcp
  194. soupault
  195. spectrum >= "0.7.0"
  196. spectrum_capabilities
  197. spectrum_palette_ppx
  198. spectrum_tools
  199. spoc
  200. statocaml_profile
  201. stem
  202. swagger
  203. talon < "1.0.0~alpha3"
  204. testcontainers
  205. testo
  206. testo-lwt
  207. testo-util
  208. tezt
  209. timere-parse
  210. touist >= "3.5.0"
  211. tyre >= "0.4"
  212. tyxml >= "4.2.0"
  213. tyxml-syntax
  214. uri < "4.0.0"
  215. uri-re
  216. user-agent-parser
  217. user-setup
  218. uuuu < "0.4.0"
  219. validate
  220. vendredi
  221. wasm_of_ocaml-compiler
  222. webmachine
  223. wire
  224. xtmpl >= "0.18.0"

Conflicts

None