335 lines
12 KiB
Groff
335 lines
12 KiB
Groff
.TH PCREBUILD 3
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.SH NAME
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PCRE - Perl-compatible regular expressions
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.SH "PCRE BUILD-TIME OPTIONS"
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.rs
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.sp
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This document describes the optional features of PCRE that can be selected when
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the library is compiled. It assumes use of the \fBconfigure\fP script, where
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the optional features are selected or deselected by providing options to
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\fBconfigure\fP before running the \fBmake\fP command. However, the same
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options can be selected in both Unix-like and non-Unix-like environments using
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the GUI facility of \fBCMakeSetup\fP if you are using \fBCMake\fP instead of
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\fBconfigure\fP to build PCRE.
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.P
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The complete list of options for \fBconfigure\fP (which includes the standard
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ones such as the selection of the installation directory) can be obtained by
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running
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.sp
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./configure --help
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.sp
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The following sections include descriptions of options whose names begin with
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--enable or --disable. These settings specify changes to the defaults for the
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\fBconfigure\fP command. Because of the way that \fBconfigure\fP works,
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--enable and --disable always come in pairs, so the complementary option always
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exists as well, but as it specifies the default, it is not described.
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.
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.SH "C++ SUPPORT"
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.rs
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.sp
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By default, the \fBconfigure\fP script will search for a C++ compiler and C++
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header files. If it finds them, it automatically builds the C++ wrapper library
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for PCRE. You can disable this by adding
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.sp
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--disable-cpp
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.sp
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to the \fBconfigure\fP command.
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.
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.SH "UTF-8 SUPPORT"
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.rs
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.sp
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To build PCRE with support for UTF-8 Unicode character strings, add
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.sp
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--enable-utf8
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.sp
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to the \fBconfigure\fP command. Of itself, this does not make PCRE treat
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strings as UTF-8. As well as compiling PCRE with this option, you also have
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have to set the PCRE_UTF8 option when you call the \fBpcre_compile()\fP
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function.
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.P
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If you set --enable-utf8 when compiling in an EBCDIC environment, PCRE expects
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its input to be either ASCII or UTF-8 (depending on the runtime option). It is
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not possible to support both EBCDIC and UTF-8 codes in the same version of the
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library. Consequently, --enable-utf8 and --enable-ebcdic are mutually
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exclusive.
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.
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.SH "UNICODE CHARACTER PROPERTY SUPPORT"
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.rs
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.sp
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UTF-8 support allows PCRE to process character values greater than 255 in the
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strings that it handles. On its own, however, it does not provide any
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facilities for accessing the properties of such characters. If you want to be
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able to use the pattern escapes \eP, \ep, and \eX, which refer to Unicode
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character properties, you must add
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.sp
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--enable-unicode-properties
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.sp
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to the \fBconfigure\fP command. This implies UTF-8 support, even if you have
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not explicitly requested it.
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.P
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Including Unicode property support adds around 30K of tables to the PCRE
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library. Only the general category properties such as \fILu\fP and \fINd\fP are
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supported. Details are given in the
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.\" HREF
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\fBpcrepattern\fP
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.\"
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documentation.
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.
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.SH "CODE VALUE OF NEWLINE"
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.rs
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.sp
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By default, PCRE interprets the linefeed (LF) character as indicating the end
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of a line. This is the normal newline character on Unix-like systems. You can
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compile PCRE to use carriage return (CR) instead, by adding
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.sp
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--enable-newline-is-cr
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.sp
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to the \fBconfigure\fP command. There is also a --enable-newline-is-lf option,
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which explicitly specifies linefeed as the newline character.
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.sp
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Alternatively, you can specify that line endings are to be indicated by the two
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character sequence CRLF. If you want this, add
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.sp
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--enable-newline-is-crlf
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.sp
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to the \fBconfigure\fP command. There is a fourth option, specified by
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.sp
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--enable-newline-is-anycrlf
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.sp
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which causes PCRE to recognize any of the three sequences CR, LF, or CRLF as
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indicating a line ending. Finally, a fifth option, specified by
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.sp
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--enable-newline-is-any
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.sp
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causes PCRE to recognize any Unicode newline sequence.
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.P
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Whatever line ending convention is selected when PCRE is built can be
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overridden when the library functions are called. At build time it is
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conventional to use the standard for your operating system.
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.
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.SH "WHAT \eR MATCHES"
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.rs
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.sp
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By default, the sequence \eR in a pattern matches any Unicode newline sequence,
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whatever has been selected as the line ending sequence. If you specify
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.sp
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--enable-bsr-anycrlf
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.sp
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the default is changed so that \eR matches only CR, LF, or CRLF. Whatever is
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selected when PCRE is built can be overridden when the library functions are
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called.
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.
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.SH "BUILDING SHARED AND STATIC LIBRARIES"
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.rs
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.sp
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The PCRE building process uses \fBlibtool\fP to build both shared and static
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Unix libraries by default. You can suppress one of these by adding one of
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.sp
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--disable-shared
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--disable-static
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.sp
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to the \fBconfigure\fP command, as required.
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.
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.SH "POSIX MALLOC USAGE"
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.rs
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.sp
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When PCRE is called through the POSIX interface (see the
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.\" HREF
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\fBpcreposix\fP
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.\"
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documentation), additional working storage is required for holding the pointers
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to capturing substrings, because PCRE requires three integers per substring,
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whereas the POSIX interface provides only two. If the number of expected
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substrings is small, the wrapper function uses space on the stack, because this
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is faster than using \fBmalloc()\fP for each call. The default threshold above
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which the stack is no longer used is 10; it can be changed by adding a setting
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such as
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.sp
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--with-posix-malloc-threshold=20
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.sp
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to the \fBconfigure\fP command.
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.
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.SH "HANDLING VERY LARGE PATTERNS"
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.rs
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.sp
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Within a compiled pattern, offset values are used to point from one part to
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another (for example, from an opening parenthesis to an alternation
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metacharacter). By default, two-byte values are used for these offsets, leading
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to a maximum size for a compiled pattern of around 64K. This is sufficient to
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handle all but the most gigantic patterns. Nevertheless, some people do want to
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process enormous patterns, so it is possible to compile PCRE to use three-byte
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or four-byte offsets by adding a setting such as
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.sp
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--with-link-size=3
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.sp
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to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
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longer offsets slows down the operation of PCRE because it has to load
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additional bytes when handling them.
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.
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.SH "AVOIDING EXCESSIVE STACK USAGE"
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.rs
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.sp
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When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
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by making recursive calls to an internal function called \fBmatch()\fP. In
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environments where the size of the stack is limited, this can severely limit
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PCRE's operation. (The Unix environment does not usually suffer from this
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problem, but it may sometimes be necessary to increase the maximum stack size.
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There is a discussion in the
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.\" HREF
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\fBpcrestack\fP
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.\"
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documentation.) An alternative approach to recursion that uses memory from the
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heap to remember data, instead of using recursive function calls, has been
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implemented to work round the problem of limited stack size. If you want to
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build a version of PCRE that works this way, add
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.sp
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--disable-stack-for-recursion
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.sp
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to the \fBconfigure\fP command. With this configuration, PCRE will use the
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\fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
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management functions. By default these point to \fBmalloc()\fP and
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\fBfree()\fP, but you can replace the pointers so that your own functions are
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used.
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.P
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Separate functions are provided rather than using \fBpcre_malloc\fP and
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\fBpcre_free\fP because the usage is very predictable: the block sizes
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requested are always the same, and the blocks are always freed in reverse
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order. A calling program might be able to implement optimized functions that
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perform better than \fBmalloc()\fP and \fBfree()\fP. PCRE runs noticeably more
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slowly when built in this way. This option affects only the \fBpcre_exec()\fP
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function; it is not relevant for the the \fBpcre_dfa_exec()\fP function.
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.
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.SH "LIMITING PCRE RESOURCE USAGE"
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.rs
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.sp
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Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
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(sometimes recursively) when matching a pattern with the \fBpcre_exec()\fP
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function. By controlling the maximum number of times this function may be
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called during a single matching operation, a limit can be placed on the
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resources used by a single call to \fBpcre_exec()\fP. The limit can be changed
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at run time, as described in the
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.\" HREF
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\fBpcreapi\fP
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.\"
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documentation. The default is 10 million, but this can be changed by adding a
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setting such as
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.sp
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--with-match-limit=500000
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.sp
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to the \fBconfigure\fP command. This setting has no effect on the
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\fBpcre_dfa_exec()\fP matching function.
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.P
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In some environments it is desirable to limit the depth of recursive calls of
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\fBmatch()\fP more strictly than the total number of calls, in order to
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restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion
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is specified) that is used. A second limit controls this; it defaults to the
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value that is set for --with-match-limit, which imposes no additional
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constraints. However, you can set a lower limit by adding, for example,
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.sp
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--with-match-limit-recursion=10000
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.sp
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to the \fBconfigure\fP command. This value can also be overridden at run time.
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.
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.SH "CREATING CHARACTER TABLES AT BUILD TIME"
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.rs
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.sp
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PCRE uses fixed tables for processing characters whose code values are less
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than 256. By default, PCRE is built with a set of tables that are distributed
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in the file \fIpcre_chartables.c.dist\fP. These tables are for ASCII codes
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only. If you add
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.sp
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--enable-rebuild-chartables
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.sp
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to the \fBconfigure\fP command, the distributed tables are no longer used.
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Instead, a program called \fBdftables\fP is compiled and run. This outputs the
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source for new set of tables, created in the default locale of your C runtime
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system. (This method of replacing the tables does not work if you are cross
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compiling, because \fBdftables\fP is run on the local host. If you need to
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create alternative tables when cross compiling, you will have to do so "by
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hand".)
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.
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.SH "USING EBCDIC CODE"
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.rs
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.sp
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PCRE assumes by default that it will run in an environment where the character
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code is ASCII (or Unicode, which is a superset of ASCII). This is the case for
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most computer operating systems. PCRE can, however, be compiled to run in an
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EBCDIC environment by adding
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.sp
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--enable-ebcdic
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.sp
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to the \fBconfigure\fP command. This setting implies
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--enable-rebuild-chartables. You should only use it if you know that you are in
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an EBCDIC environment (for example, an IBM mainframe operating system). The
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--enable-ebcdic option is incompatible with --enable-utf8.
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.
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.SH "PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT"
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.rs
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.sp
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By default, \fBpcregrep\fP reads all files as plain text. You can build it so
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that it recognizes files whose names end in \fB.gz\fP or \fB.bz2\fP, and reads
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them with \fBlibz\fP or \fBlibbz2\fP, respectively, by adding one or both of
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.sp
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--enable-pcregrep-libz
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--enable-pcregrep-libbz2
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.sp
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to the \fBconfigure\fP command. These options naturally require that the
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relevant libraries are installed on your system. Configuration will fail if
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they are not.
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.
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.SH "PCRETEST OPTION FOR LIBREADLINE SUPPORT"
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.rs
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.sp
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If you add
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.sp
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--enable-pcretest-libreadline
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.sp
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to the \fBconfigure\fP command, \fBpcretest\fP is linked with the
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\fBlibreadline\fP library, and when its input is from a terminal, it reads it
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using the \fBreadline()\fP function. This provides line-editing and history
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facilities. Note that \fBlibreadline\fP is GPL-licenced, so if you distribute a
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binary of \fBpcretest\fP linked in this way, there may be licensing issues.
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.P
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Setting this option causes the \fB-lreadline\fP option to be added to the
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\fBpcretest\fP build. In many operating environments with a sytem-installed
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\fBlibreadline\fP this is sufficient. However, in some environments (e.g.
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if an unmodified distribution version of readline is in use), some extra
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configuration may be necessary. The INSTALL file for \fBlibreadline\fP says
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this:
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.sp
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"Readline uses the termcap functions, but does not link with the
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termcap or curses library itself, allowing applications which link
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with readline the to choose an appropriate library."
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.sp
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If your environment has not been set up so that an appropriate library is
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automatically included, you may need to add something like
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.sp
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LIBS="-ncurses"
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.sp
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immediately before the \fBconfigure\fP command.
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.
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.
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.SH "SEE ALSO"
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.rs
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.sp
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\fBpcreapi\fP(3), \fBpcre_config\fP(3).
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.
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.
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.SH AUTHOR
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.rs
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.sp
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.nf
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Philip Hazel
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University Computing Service
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Cambridge CB2 3QH, England.
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.fi
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.
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.
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.SH REVISION
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.rs
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.sp
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.nf
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Last updated: 17 March 2009
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Copyright (c) 1997-2009 University of Cambridge.
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.fi
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