Windows PowerShell command on Get-command pcre

Manual Pages for UNIX Operating System command usage for man pcre

Introduction to Library Functions PCRE(3)

NAME

PCRE - Perl-compatible regular expressions

INTRODUCTION

The PCRE library is a set of functions that implement regu-

lar expression pattern matching using the same syntax and semantics as Perl, with just a few differences. Certain features that appeared in Python and PCRE before they appeared in Perl are also available using the Python syntax. There is also some support for certain .NET and Oniguruma syntax items, and there is an option for requesting some minor changes that give better JavaScript compatibility. The current implementation of PCRE (release 7.x) corresponds

approximately with Perl 5.10, including support for UTF-8

encoded strings and Unicode general category properties.

However, UTF-8 and Unicode support has to be explicitly

enabled; it is not the default. The Unicode tables correspond to Unicode release 5.0.0.

In addition to the Perl-compatible matching function, PCRE

contains an alternative matching function that matches the

same compiled patterns in a different way. In certain cir-

cumstances, the alternative function has some advantages. For a discussion of the two matching algorithms, see the

pcrematching page.

PCRE is written in C and released as a C library. A number of people have written wrappers and interfaces of various kinds. In particular, Google Inc. have provided a comprehensive C++ wrapper. This is now included as part of

the PCRE distribution. The pcrecpp page has details of this

interface. Other people's contributions can be found in the Contrib directory at the primary FTP site, which is:

ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre

Details of exactly which Perl regular expression features are and are not supported by PCRE are given in separate

documents. See the pcrepattern and pcrecompat pages. There

is a syntax summary in the pcresyntax page.

Some features of PCRE can be included, excluded, or changed

when the library is built. The pcre_config() function makes

it possible for a client to discover which features are available. The features themselves are described in the

pcrebuild page. Documentation about building PCRE for vari-

ous operating systems can be found in the README file in the source distribution. SunOS 5.10 Last change: 1 Introduction to Library Functions PCRE(3)

The library contains a number of undocumented internal func-

tions and data tables that are used by more than one of the exported external functions, but which are not intended for use by external callers. Their names all begin with

"_pcre_", which hopefully will not provoke any name clashes.

In some environments, it is possible to control which exter-

nal symbols are exported when a shared library is built, and in these cases the undocumented symbols are not exported. USER DOCUMENTATION

The user documentation for PCRE comprises a number of dif-

ferent sections. In the "man" format, each of these is a separate "man page". In the HTML format, each is a separate page, linked from the index page. In the plain text format, all the sections are concatenated, for ease of searching. The sections are as follows:

pcre this document

pcre-config show PCRE installation configuration

information

pcreapi details of PCRE's native C API

pcrebuild options for building PCRE

pcrecallout details of the callout feature

pcrecompat discussion of Perl compatibility

pcrecpp details of the C++ wrapper

pcregrep description of the pcregrep command

pcrematching discussion of the two matching algo-

rithms

pcrepartial details of the partial matching facility

pcrepattern syntax and semantics of supported

regular expressions

pcresyntax quick syntax reference

pcreperform discussion of performance issues

pcreposix the POSIX-compatible C API

pcreprecompile details of saving and re-using precom-

piled patterns

pcresample discussion of the sample program

pcrestack discussion of stack usage

pcretest description of the pcretest testing com-

mand In addition, in the "man" and HTML formats, there is a short page for each C library function, listing its arguments and results. LIMITATIONS There are some size limitations in PCRE but it is hoped that they will never in practice be relevant. SunOS 5.10 Last change: 2 Introduction to Library Functions PCRE(3) The maximum length of a compiled pattern is 65539 (sic) bytes if PCRE is compiled with the default internal linkage size of 2. If you want to process regular expressions that are truly enormous, you can compile PCRE with an internal linkage size of 3 or 4 (see the README file in the source

distribution and the pcrebuild documentation for details).

In these cases the limit is substantially larger. However, the speed of execution is slower. All values in repeating quantifiers must be less than 65536.

There is no limit to the number of parenthesized subpat-

terns, but there can be no more than 65535 capturing subpat-

terns. The maximum length of name for a named subpattern is 32 characters, and the maximum number of named subpatterns is 10000.

The maximum length of a subject string is the largest posi-

tive number that an integer variable can hold. However, when using the traditional matching function, PCRE uses recursion to handle subpatterns and indefinite repetition. This means

that the available stack space may limit the size of a sub-

ject string that can be processed by certain patterns. For a

discussion of stack issues, see the pcrestack documentation.

UTF-8 AND UNICODE PROPERTY SUPPORT

From release 3.3, PCRE has had some support for character

strings encoded in the UTF-8 format. For release 4.0 this

was greatly extended to cover most common requirements, and in release 5.0 additional support for Unicode general category properties was added.

In order process UTF-8 strings, you must build PCRE to

include UTF-8 support in the code, and, in addition, you

must call pcre_compile() with the PCRE_UTF8 option flag.

When you do this, both the pattern and any subject strings

that are matched against it are treated as UTF-8 strings

instead of just strings of bytes.

If you compile PCRE with UTF-8 support, but do not use it at

run time, the library will be a bit bigger, but the addi-

tional run time overhead is limited to testing the PCRE_UTF8

flag occasionally, so should not be very big. If PCRE is built with Unicode character property support

(which implies UTF-8 support), the escape sequences \p{..},

\P{..}, and \X are supported. The available properties that can be tested are limited to the general category properties such as Lu for an upper case letter or Nd for a decimal SunOS 5.10 Last change: 3 Introduction to Library Functions PCRE(3) number, the Unicode script names such as Arabic or Han, and the derived properties Any and L&. A full list is given in

the pcrepattern documentation. Only the short names for pro-

perties are supported. For example, \p{L} matches a letter.

Its Perl synonym, \p{Letter}, is not supported. Further-

more, in Perl, many properties may optionally be prefixed by "Is", for compatibility with Perl 5.6. PCRE does not support this.

Validity of UTF-8 strings

When you set the PCRE_UTF8 flag, the strings passed as pat-

terns and subjects are (by default) checked for validity on entry to the relevant functions. From release 7.3 of PCRE, the check is according the rules of RFC 3629, which are themselves derived from the Unicode specification. Earlier releases of PCRE followed the rules of RFC 2279, which

allows the full range of 31-bit values (0 to 0x7FFFFFFF).

The current check allows only values in the range U+0 to U+10FFFF, excluding U+D800 to U+DFFF. The excluded code points are the "Low Surrogate Area" of Unicode, of which the Unicode Standard says this: "The Low Surrogate Area does not contain any character assignments,

consequently no character code charts or namelists are pro-

vided for this area. Surrogates are reserved for use with

UTF-16 and then must be used in pairs." The code points that

are encoded by UTF-16 pairs are available as independent

code points in the UTF-8 encoding. (In other words, the

whole surrogate thing is a fudge for UTF-16 which unfor-

tunately messes up UTF-8.)

If an invalid UTF-8 string is passed to PCRE, an error

return (PCRE_ERROR_BADUTF8) is given. In some situations,

you may already know that your strings are valid, and there-

fore want to skip these checks in order to improve perfor-

mance. If you set the PCRE_NO_UTF8_CHECK flag at compile

time or at run time, PCRE assumes that the pattern or sub-

ject it is given (respectively) contains only valid UTF-8

codes. In this case, it does not diagnose an invalid UTF-8

string.

If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK

is set, what happens depends on why the string is invalid.

If the string conforms to the "old" definition of UTF-8 (RFC

2279), it is processed as a string of characters in the

range 0 to 0x7FFFFFFF. In other words, apart from the ini-

tial validity test, PCRE (when in UTF-8 mode) handles

strings according to the more liberal rules of RFC 2279. However, if the string does not even conform to RFC 2279, the result is undefined. Your program may crash. SunOS 5.10 Last change: 4 Introduction to Library Functions PCRE(3) If you want to process strings of values in the full range 0

to 0x7FFFFFFF, encoded in a UTF-8-like manner as per the old

RFC, you can set PCRE_NO_UTF8_CHECK to bypass the more res-

trictive test. However, in this situation, you will have to apply your own validity check.

General comments about UTF-8 mode

1. An unbraced hexadecimal escape sequence (such as \xb3)

matches a two-byte UTF-8 character if the value is greater

than 127.

2. Octal numbers up to \777 are recognized, and match two-

byte UTF-8 characters for values greater than \177.

3. Repeat quantifiers apply to complete UTF-8 characters,

not to individual bytes, for example: \x{100}{3}.

4. The dot metacharacter matches one UTF-8 character instead

of a single byte. 5. The escape sequence \C can be used to match a single byte

in UTF-8 mode, but its use can lead to some strange effects.

This facility is not available in the alternative matching

function, pcre_dfa_exec().

6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W

correctly test characters of any code value, but the charac-

ters that PCRE recognizes as digits, spaces, or word charac-

ters remain the same set as before, all with values less than 256. This remains true even when PCRE includes Unicode property support, because to do otherwise would slow down PCRE in many common cases. If you really want to test for a wider sense of, say, "digit", you must use Unicode property tests such as \p{Nd}.

7. Similarly, characters that match the POSIX named charac-

ter classes are all low-valued characters.

8. However, the Perl 5.10 horizontal and vertical whitespace matching escapes (\h, \H, \v, and \V) do match all the appropriate Unicode characters.

9. Case-insensitive matching applies only to characters

whose values are less than 128, unless PCRE is built with Unicode property support. Even when Unicode property support is available, PCRE still uses its own character tables when

checking the case of low-valued characters, so as not to

degrade performance. The Unicode property information is used only for characters with higher values. Even when

Unicode property support is available, PCRE supports case-

insensitive matching only when there is a one-to-one mapping

SunOS 5.10 Last change: 5 Introduction to Library Functions PCRE(3)

between a letter's cases. There are a small number of many-

to-one mappings in Unicode; these are not supported by PCRE.

AUTHOR Philip Hazel University Computing Service Cambridge CB2 3QH, England. Putting an actual email address here seems to have been a spam magnet, so I've taken it away. If you want to email me, use my two initials, followed by the two digits 10, at the domain cam.ac.uk. REVISION Last updated: 12 April 2008

ATTRIBUTES

See attributes(5) for descriptions of the following attri-

butes:

_______________________________________

| ATTRIBUTE TYPE | ATTRIBUTE VALUE|

|____________________|__________________|_

| Availability | library/pcre |

|____________________|__________________|_

| Interface Stability| Uncommitted |

|____________________|_________________|

NOTES Source for PCRE is available on http://opensolaris.org. SunOS 5.10 Last change: 6