pcre.3 9.1 KB

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  1. .TH PCRE 3 "10 February 2015" "PCRE 8.37"
  2. .SH NAME
  3. PCRE - Perl-compatible regular expressions (original API)
  4. .SH "PLEASE TAKE NOTE"
  5. .rs
  6. .sp
  7. This document relates to PCRE releases that use the original API,
  8. with library names libpcre, libpcre16, and libpcre32. January 2015 saw the
  9. first release of a new API, known as PCRE2, with release numbers starting at
  10. 10.00 and library names libpcre2-8, libpcre2-16, and libpcre2-32. The old
  11. libraries (now called PCRE1) are still being maintained for bug fixes, but
  12. there will be no new development. New projects are advised to use the new PCRE2
  13. libraries.
  14. .
  15. .
  16. .SH INTRODUCTION
  17. .rs
  18. .sp
  19. The PCRE library is a set of functions that implement regular expression
  20. pattern matching using the same syntax and semantics as Perl, with just a few
  21. differences. Some features that appeared in Python and PCRE before they
  22. appeared in Perl are also available using the Python syntax, there is some
  23. support for one or two .NET and Oniguruma syntax items, and there is an option
  24. for requesting some minor changes that give better JavaScript compatibility.
  25. .P
  26. Starting with release 8.30, it is possible to compile two separate PCRE
  27. libraries: the original, which supports 8-bit character strings (including
  28. UTF-8 strings), and a second library that supports 16-bit character strings
  29. (including UTF-16 strings). The build process allows either one or both to be
  30. built. The majority of the work to make this possible was done by Zoltan
  31. Herczeg.
  32. .P
  33. Starting with release 8.32 it is possible to compile a third separate PCRE
  34. library that supports 32-bit character strings (including UTF-32 strings). The
  35. build process allows any combination of the 8-, 16- and 32-bit libraries. The
  36. work to make this possible was done by Christian Persch.
  37. .P
  38. The three libraries contain identical sets of functions, except that the names
  39. in the 16-bit library start with \fBpcre16_\fP instead of \fBpcre_\fP, and the
  40. names in the 32-bit library start with \fBpcre32_\fP instead of \fBpcre_\fP. To
  41. avoid over-complication and reduce the documentation maintenance load, most of
  42. the documentation describes the 8-bit library, with the differences for the
  43. 16-bit and 32-bit libraries described separately in the
  44. .\" HREF
  45. \fBpcre16\fP
  46. and
  47. .\" HREF
  48. \fBpcre32\fP
  49. .\"
  50. pages. References to functions or structures of the form \fIpcre[16|32]_xxx\fP
  51. should be read as meaning "\fIpcre_xxx\fP when using the 8-bit library,
  52. \fIpcre16_xxx\fP when using the 16-bit library, or \fIpcre32_xxx\fP when using
  53. the 32-bit library".
  54. .P
  55. The current implementation of PCRE corresponds approximately with Perl 5.12,
  56. including support for UTF-8/16/32 encoded strings and Unicode general category
  57. properties. However, UTF-8/16/32 and Unicode support has to be explicitly
  58. enabled; it is not the default. The Unicode tables correspond to Unicode
  59. release 6.3.0.
  60. .P
  61. In addition to the Perl-compatible matching function, PCRE contains an
  62. alternative function that matches the same compiled patterns in a different
  63. way. In certain circumstances, the alternative function has some advantages.
  64. For a discussion of the two matching algorithms, see the
  65. .\" HREF
  66. \fBpcrematching\fP
  67. .\"
  68. page.
  69. .P
  70. PCRE is written in C and released as a C library. A number of people have
  71. written wrappers and interfaces of various kinds. In particular, Google Inc.
  72. have provided a comprehensive C++ wrapper for the 8-bit library. This is now
  73. included as part of the PCRE distribution. The
  74. .\" HREF
  75. \fBpcrecpp\fP
  76. .\"
  77. page has details of this interface. Other people's contributions can be found
  78. in the \fIContrib\fP directory at the primary FTP site, which is:
  79. .sp
  80. .\" HTML <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">
  81. .\" </a>
  82. ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
  83. .\"
  84. .P
  85. Details of exactly which Perl regular expression features are and are not
  86. supported by PCRE are given in separate documents. See the
  87. .\" HREF
  88. \fBpcrepattern\fP
  89. .\"
  90. and
  91. .\" HREF
  92. \fBpcrecompat\fP
  93. .\"
  94. pages. There is a syntax summary in the
  95. .\" HREF
  96. \fBpcresyntax\fP
  97. .\"
  98. page.
  99. .P
  100. Some features of PCRE can be included, excluded, or changed when the library is
  101. built. The
  102. .\" HREF
  103. \fBpcre_config()\fP
  104. .\"
  105. function makes it possible for a client to discover which features are
  106. available. The features themselves are described in the
  107. .\" HREF
  108. \fBpcrebuild\fP
  109. .\"
  110. page. Documentation about building PCRE for various operating systems can be
  111. found in the
  112. .\" HTML <a href="README.txt">
  113. .\" </a>
  114. \fBREADME\fP
  115. .\"
  116. and
  117. .\" HTML <a href="NON-AUTOTOOLS-BUILD.txt">
  118. .\" </a>
  119. \fBNON-AUTOTOOLS_BUILD\fP
  120. .\"
  121. files in the source distribution.
  122. .P
  123. The libraries contains a number of undocumented internal functions and data
  124. tables that are used by more than one of the exported external functions, but
  125. which are not intended for use by external callers. Their names all begin with
  126. "_pcre_" or "_pcre16_" or "_pcre32_", which hopefully will not provoke any name
  127. clashes. In some environments, it is possible to control which external symbols
  128. are exported when a shared library is built, and in these cases the
  129. undocumented symbols are not exported.
  130. .
  131. .
  132. .SH "SECURITY CONSIDERATIONS"
  133. .rs
  134. .sp
  135. If you are using PCRE in a non-UTF application that permits users to supply
  136. arbitrary patterns for compilation, you should be aware of a feature that
  137. allows users to turn on UTF support from within a pattern, provided that PCRE
  138. was built with UTF support. For example, an 8-bit pattern that begins with
  139. "(*UTF8)" or "(*UTF)" turns on UTF-8 mode, which interprets patterns and
  140. subjects as strings of UTF-8 characters instead of individual 8-bit characters.
  141. This causes both the pattern and any data against which it is matched to be
  142. checked for UTF-8 validity. If the data string is very long, such a check might
  143. use sufficiently many resources as to cause your application to lose
  144. performance.
  145. .P
  146. One way of guarding against this possibility is to use the
  147. \fBpcre_fullinfo()\fP function to check the compiled pattern's options for UTF.
  148. Alternatively, from release 8.33, you can set the PCRE_NEVER_UTF option at
  149. compile time. This causes an compile time error if a pattern contains a
  150. UTF-setting sequence.
  151. .P
  152. If your application is one that supports UTF, be aware that validity checking
  153. can take time. If the same data string is to be matched many times, you can use
  154. the PCRE_NO_UTF[8|16|32]_CHECK option for the second and subsequent matches to
  155. save redundant checks.
  156. .P
  157. Another way that performance can be hit is by running a pattern that has a very
  158. large search tree against a string that will never match. Nested unlimited
  159. repeats in a pattern are a common example. PCRE provides some protection
  160. against this: see the PCRE_EXTRA_MATCH_LIMIT feature in the
  161. .\" HREF
  162. \fBpcreapi\fP
  163. .\"
  164. page.
  165. .
  166. .
  167. .SH "USER DOCUMENTATION"
  168. .rs
  169. .sp
  170. The user documentation for PCRE comprises a number of different sections. In
  171. the "man" format, each of these is a separate "man page". In the HTML format,
  172. each is a separate page, linked from the index page. In the plain text format,
  173. the descriptions of the \fBpcregrep\fP and \fBpcretest\fP programs are in files
  174. called \fBpcregrep.txt\fP and \fBpcretest.txt\fP, respectively. The remaining
  175. sections, except for the \fBpcredemo\fP section (which is a program listing),
  176. are concatenated in \fBpcre.txt\fP, for ease of searching. The sections are as
  177. follows:
  178. .sp
  179. pcre this document
  180. pcre-config show PCRE installation configuration information
  181. pcre16 details of the 16-bit library
  182. pcre32 details of the 32-bit library
  183. pcreapi details of PCRE's native C API
  184. pcrebuild building PCRE
  185. pcrecallout details of the callout feature
  186. pcrecompat discussion of Perl compatibility
  187. pcrecpp details of the C++ wrapper for the 8-bit library
  188. pcredemo a demonstration C program that uses PCRE
  189. pcregrep description of the \fBpcregrep\fP command (8-bit only)
  190. pcrejit discussion of the just-in-time optimization support
  191. pcrelimits details of size and other limits
  192. pcrematching discussion of the two matching algorithms
  193. pcrepartial details of the partial matching facility
  194. .\" JOIN
  195. pcrepattern syntax and semantics of supported
  196. regular expressions
  197. pcreperform discussion of performance issues
  198. pcreposix the POSIX-compatible C API for the 8-bit library
  199. pcreprecompile details of saving and re-using precompiled patterns
  200. pcresample discussion of the pcredemo program
  201. pcrestack discussion of stack usage
  202. pcresyntax quick syntax reference
  203. pcretest description of the \fBpcretest\fP testing command
  204. pcreunicode discussion of Unicode and UTF-8/16/32 support
  205. .sp
  206. In the "man" and HTML formats, there is also a short page for each C library
  207. function, listing its arguments and results.
  208. .
  209. .
  210. .SH AUTHOR
  211. .rs
  212. .sp
  213. .nf
  214. Philip Hazel
  215. University Computing Service
  216. Cambridge CB2 3QH, England.
  217. .fi
  218. .P
  219. Putting an actual email address here seems to have been a spam magnet, so I've
  220. taken it away. If you want to email me, use my two initials, followed by the
  221. two digits 10, at the domain cam.ac.uk.
  222. .
  223. .
  224. .SH REVISION
  225. .rs
  226. .sp
  227. .nf
  228. Last updated: 10 February 2015
  229. Copyright (c) 1997-2015 University of Cambridge.
  230. .fi