.TH PCRE2BUILD 3 "07 October 2016" "PCRE2 10.23"
.SH NAME
PCRE2 - Perl-compatible regular expressions (revised API)
.
.
.SH "BUILDING PCRE2"
.rs
.sp
PCRE2 is distributed with a \fBconfigure\fP script that can be used to build
the library in Unix-like environments using the applications known as
Autotools. Also in the distribution are files to support building using
\fBCMake\fP instead of \fBconfigure\fP. The text file
.\" HTML <a href="README.txt">
.\" </a>
\fBREADME\fP
.\"
contains general information about building with Autotools (some of which is
repeated below), and also has some comments about building on various operating
systems. There is a lot more information about building PCRE2 without using
Autotools (including information about using \fBCMake\fP and building "by
hand") in the text file called
.\" HTML <a href="NON-AUTOTOOLS-BUILD.txt">
.\" </a>
\fBNON-AUTOTOOLS-BUILD\fP.
.\"
You should consult this file as well as the
.\" HTML <a href="README.txt">
.\" </a>
\fBREADME\fP
.\"
file if you are building in a non-Unix-like environment.
.
.
.SH "PCRE2 BUILD-TIME OPTIONS"
.rs
.sp
The rest of this document describes the optional features of PCRE2 that can be
selected when the library is compiled. It assumes use of the \fBconfigure\fP
script, where the optional features are selected or deselected by providing
options to \fBconfigure\fP before running the \fBmake\fP command. However, the
same options can be selected in both Unix-like and non-Unix-like environments
if you are using \fBCMake\fP instead of \fBconfigure\fP to build PCRE2.
.P
If you are not using Autotools or \fBCMake\fP, option selection can be done by
editing the \fBconfig.h\fP file, or by passing parameter settings to the
compiler, as described in
.\" HTML <a href="NON-AUTOTOOLS-BUILD.txt">
.\" </a>
\fBNON-AUTOTOOLS-BUILD\fP.
.\"
.P
The complete list of options for \fBconfigure\fP (which includes the standard
ones such as the selection of the installation directory) can be obtained by
running
.sp
  ./configure --help
.sp
The following sections include descriptions of options whose names begin with
--enable or --disable. These settings specify changes to the defaults for the
\fBconfigure\fP command. Because of the way that \fBconfigure\fP works,
--enable and --disable always come in pairs, so the complementary option always
exists as well, but as it specifies the default, it is not described.
.
.
.SH "BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES"
.rs
.sp
By default, a library called \fBlibpcre2-8\fP is built, containing functions
that take string arguments contained in vectors of bytes, interpreted either as
single-byte characters, or UTF-8 strings. You can also build two other
libraries, called \fBlibpcre2-16\fP and \fBlibpcre2-32\fP, which process
strings that are contained in vectors of 16-bit and 32-bit code units,
respectively. These can be interpreted either as single-unit characters or
UTF-16/UTF-32 strings. To build these additional libraries, add one or both of
the following to the \fBconfigure\fP command:
.sp
  --enable-pcre2-16
  --enable-pcre2-32
.sp
If you do not want the 8-bit library, add
.sp
  --disable-pcre2-8
.sp
as well. At least one of the three libraries must be built. Note that the POSIX
wrapper is for the 8-bit library only, and that \fBpcre2grep\fP is an 8-bit
program. Neither of these are built if you select only the 16-bit or 32-bit
libraries.
.
.
.SH "BUILDING SHARED AND STATIC LIBRARIES"
.rs
.sp
The Autotools PCRE2 building process uses \fBlibtool\fP to build both shared
and static libraries by default. You can suppress an unwanted library by adding
one of
.sp
  --disable-shared
  --disable-static
.sp
to the \fBconfigure\fP command.
.
.
.SH "UNICODE AND UTF SUPPORT"
.rs
.sp
By default, PCRE2 is built with support for Unicode and UTF character strings.
To build it without Unicode support, add
.sp
  --disable-unicode
.sp
to the \fBconfigure\fP command. This setting applies to all three libraries. It
is not possible to build one library with Unicode support, and another without,
in the same configuration.
.P
Of itself, Unicode support does not make PCRE2 treat strings as UTF-8, UTF-16
or UTF-32. To do that, applications that use the library can set the PCRE2_UTF
option when they call \fBpcre2_compile()\fP to compile a pattern.
Alternatively, patterns may be started with (*UTF) unless the application has
locked this out by setting PCRE2_NEVER_UTF.
.P
UTF support allows the libraries to process character code points up to
0x10ffff in the strings that they handle. It also provides support for
accessing the Unicode properties of such characters, using pattern escapes such
as \eP, \ep, and \eX. Only the general category properties such as \fILu\fP and
\fINd\fP are supported. Details are given in the
.\" HREF
\fBpcre2pattern\fP
.\"
documentation.
.P
Pattern escapes such as \ed and \ew do not by default make use of Unicode
properties. The application can request that they do by setting the PCRE2_UCP
option. Unless the application has set PCRE2_NEVER_UCP, a pattern may also
request this by starting with (*UCP).
.
.
.SH "DISABLING THE USE OF \eC"
.rs
.sp
The \eC escape sequence, which matches a single code unit, even in a UTF mode,
can cause unpredictable behaviour because it may leave the current matching
point in the middle of a multi-code-unit character. The application can lock it
out by setting the PCRE2_NEVER_BACKSLASH_C option when calling
\fBpcre2_compile()\fP. There is also a build-time option
.sp
  --enable-never-backslash-C
.sp
(note the upper case C) which locks out the use of \eC entirely.
.
.
.SH "JUST-IN-TIME COMPILER SUPPORT"
.rs
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Just-in-time compiler support is included in the build by specifying
.sp
  --enable-jit
.sp
This support is available only for certain hardware architectures. If this
option is set for an unsupported architecture, a building error occurs.
See the
.\" HREF
\fBpcre2jit\fP
.\"
documentation for a discussion of JIT usage. When JIT support is enabled,
pcre2grep automatically makes use of it, unless you add
.sp
  --disable-pcre2grep-jit
.sp
to the "configure" command.
.
.
.SH "NEWLINE RECOGNITION"
.rs
.sp
By default, PCRE2 interprets the linefeed (LF) character as indicating the end
of a line. This is the normal newline character on Unix-like systems. You can
compile PCRE2 to use carriage return (CR) instead, by adding
.sp
  --enable-newline-is-cr
.sp
to the \fBconfigure\fP command. There is also an --enable-newline-is-lf option,
which explicitly specifies linefeed as the newline character.
.P
Alternatively, you can specify that line endings are to be indicated by the
two-character sequence CRLF (CR immediately followed by LF). If you want this,
add
.sp
  --enable-newline-is-crlf
.sp
to the \fBconfigure\fP command. There is a fourth option, specified by
.sp
  --enable-newline-is-anycrlf
.sp
which causes PCRE2 to recognize any of the three sequences CR, LF, or CRLF as
indicating a line ending. Finally, a fifth option, specified by
.sp
  --enable-newline-is-any
.sp
causes PCRE2 to recognize any Unicode newline sequence. The Unicode newline
sequences are the three just mentioned, plus the single characters VT (vertical
tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line
separator, U+2028), and PS (paragraph separator, U+2029).
.P
Whatever default line ending convention is selected when PCRE2 is built can be
overridden by applications that use the library. At build time it is
conventional to use the standard for your operating system.
.
.
.SH "WHAT \eR MATCHES"
.rs
.sp
By default, the sequence \eR in a pattern matches any Unicode newline sequence,
independently of what has been selected as the line ending sequence. If you
specify
.sp
  --enable-bsr-anycrlf
.sp
the default is changed so that \eR matches only CR, LF, or CRLF. Whatever is
selected when PCRE2 is built can be overridden by applications that use the
called.
.
.
.SH "HANDLING VERY LARGE PATTERNS"
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.sp
Within a compiled pattern, offset values are used to point from one part to
another (for example, from an opening parenthesis to an alternation
metacharacter). By default, in the 8-bit and 16-bit libraries, two-byte values
are used for these offsets, leading to a maximum size for a compiled pattern of
around 64K code units. This is sufficient to handle all but the most gigantic
patterns. Nevertheless, some people do want to process truly enormous patterns,
so it is possible to compile PCRE2 to use three-byte or four-byte offsets by
adding a setting such as
.sp
  --with-link-size=3
.sp
to the \fBconfigure\fP command. The value given must be 2, 3, or 4. For the
16-bit library, a value of 3 is rounded up to 4. In these libraries, using
longer offsets slows down the operation of PCRE2 because it has to load
additional data when handling them. For the 32-bit library the value is always
4 and cannot be overridden; the value of --with-link-size is ignored.
.
.
.SH "AVOIDING EXCESSIVE STACK USAGE"
.rs
.sp
When matching with the \fBpcre2_match()\fP function, PCRE2 implements
backtracking by making recursive calls to an internal function called
\fBmatch()\fP. In environments where the size of the stack is limited, this can
severely limit PCRE2's operation. (The Unix environment does not usually suffer
from this problem, but it may sometimes be necessary to increase the maximum
stack size. There is a discussion in the
.\" HREF
\fBpcre2stack\fP
.\"
documentation.) An alternative approach to recursion that uses memory from the
heap to remember data, instead of using recursive function calls, has been
implemented to work round the problem of limited stack size. If you want to
build a version of PCRE2 that works this way, add
.sp
  --disable-stack-for-recursion
.sp
to the \fBconfigure\fP command. By default, the system functions \fBmalloc()\fP
and \fBfree()\fP are called to manage the heap memory that is required, but
custom memory management functions can be called instead. PCRE2 runs noticeably
more slowly when built in this way. This option affects only the
\fBpcre2_match()\fP function; it is not relevant for \fBpcre2_dfa_match()\fP.
.
.
.SH "LIMITING PCRE2 RESOURCE USAGE"
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.sp
Internally, PCRE2 has a function called \fBmatch()\fP, which it calls
repeatedly (sometimes recursively) when matching a pattern with the
\fBpcre2_match()\fP function. By controlling the maximum number of times this
function may be called during a single matching operation, a limit can be
placed on the resources used by a single call to \fBpcre2_match()\fP. The limit
can be changed at run time, as described in the
.\" HREF
\fBpcre2api\fP
.\"
documentation. The default is 10 million, but this can be changed by adding a
setting such as
.sp
  --with-match-limit=500000
.sp
to the \fBconfigure\fP command. This setting has no effect on the
\fBpcre2_dfa_match()\fP matching function.
.P
In some environments it is desirable to limit the depth of recursive calls of
\fBmatch()\fP more strictly than the total number of calls, in order to
restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion
is specified) that is used. A second limit controls this; it defaults to the
value that is set for --with-match-limit, which imposes no additional
constraints. However, you can set a lower limit by adding, for example,
.sp
  --with-match-limit-recursion=10000
.sp
to the \fBconfigure\fP command. This value can also be overridden at run time.
.
.
.SH "CREATING CHARACTER TABLES AT BUILD TIME"
.rs
.sp
PCRE2 uses fixed tables for processing characters whose code points are less
than 256. By default, PCRE2 is built with a set of tables that are distributed
in the file \fIsrc/pcre2_chartables.c.dist\fP. These tables are for ASCII codes
only. If you add
.sp
  --enable-rebuild-chartables
.sp
to the \fBconfigure\fP command, the distributed tables are no longer used.
Instead, a program called \fBdftables\fP is compiled and run. This outputs the
source for new set of tables, created in the default locale of your C run-time
system. (This method of replacing the tables does not work if you are cross
compiling, because \fBdftables\fP is run on the local host. If you need to
create alternative tables when cross compiling, you will have to do so "by
hand".)
.
.
.SH "USING EBCDIC CODE"
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.sp
PCRE2 assumes by default that it will run in an environment where the character
code is ASCII or Unicode, which is a superset of ASCII. This is the case for
most computer operating systems. PCRE2 can, however, be compiled to run in an
8-bit EBCDIC environment by adding
.sp
  --enable-ebcdic --disable-unicode
.sp
to the \fBconfigure\fP command. This setting implies
--enable-rebuild-chartables. You should only use it if you know that you are in
an EBCDIC environment (for example, an IBM mainframe operating system).
.P
It is not possible to support both EBCDIC and UTF-8 codes in the same version
of the library. Consequently, --enable-unicode and --enable-ebcdic are mutually
exclusive.
.P
The EBCDIC character that corresponds to an ASCII LF is assumed to have the
value 0x15 by default. However, in some EBCDIC environments, 0x25 is used. In
such an environment you should use
.sp
  --enable-ebcdic-nl25
.sp
as well as, or instead of, --enable-ebcdic. The EBCDIC character for CR has the
same value as in ASCII, namely, 0x0d. Whichever of 0x15 and 0x25 is \fInot\fP
chosen as LF is made to correspond to the Unicode NEL character (which, in
Unicode, is 0x85).
.P
The options that select newline behaviour, such as --enable-newline-is-cr,
and equivalent run-time options, refer to these character values in an EBCDIC
environment.
.
.
.SH "PCRE2GREP SUPPORT FOR EXTERNAL SCRIPTS"
.rs
.sp
By default, on non-Windows systems, \fBpcre2grep\fP supports the use of
callouts with string arguments within the patterns it is matching, in order to
run external scripts. For details, see the
.\" HREF
\fBpcre2grep\fP
.\"
documentation. This support can be disabled by adding
--disable-pcre2grep-callout to the \fBconfigure\fP command.
.
.
.SH "PCRE2GREP OPTIONS FOR COMPRESSED FILE SUPPORT"
.rs
.sp
By default, \fBpcre2grep\fP reads all files as plain text. You can build it so
that it recognizes files whose names end in \fB.gz\fP or \fB.bz2\fP, and reads
them with \fBlibz\fP or \fBlibbz2\fP, respectively, by adding one or both of
.sp
  --enable-pcre2grep-libz
  --enable-pcre2grep-libbz2
.sp
to the \fBconfigure\fP command. These options naturally require that the
relevant libraries are installed on your system. Configuration will fail if
they are not.
.
.
.SH "PCRE2GREP BUFFER SIZE"
.rs
.sp
\fBpcre2grep\fP uses an internal buffer to hold a "window" on the file it is
scanning, in order to be able to output "before" and "after" lines when it
finds a match. The starting size of the buffer is controlled by a parameter
whose default value is 20K. The buffer itself is three times this size, but
because of the way it is used for holding "before" lines, the longest line that
is guaranteed to be processable is the parameter size. If a longer line is 
encountered, \fBpcre2grep\fP automatically expands the buffer, up to a
specified maximum size, whose default is 1M or the starting size, whichever is
the larger. You can change the default parameter values by adding, for example,
.sp
  --with-pcre2grep-bufsize=51200
  --with-pcre2grep-max-bufsize=2097152 
.sp
to the \fBconfigure\fP command. The caller of \fPpcre2grep\fP can override 
these values by using --buffer-size and --max-buffer-size on the command line.
.
.
.SH "PCRE2TEST OPTION FOR LIBREADLINE SUPPORT"
.rs
.sp
If you add one of
.sp
  --enable-pcre2test-libreadline
  --enable-pcre2test-libedit
.sp
to the \fBconfigure\fP command, \fBpcre2test\fP is linked with the
\fBlibreadline\fP or\fBlibedit\fP library, respectively, and when its input is
from a terminal, it reads it using the \fBreadline()\fP function. This provides
line-editing and history facilities. Note that \fBlibreadline\fP is
GPL-licensed, so if you distribute a binary of \fBpcre2test\fP linked in this
way, there may be licensing issues. These can be avoided by linking instead
with \fBlibedit\fP, which has a BSD licence.
.P
Setting --enable-pcre2test-libreadline causes the \fB-lreadline\fP option to be
added to the \fBpcre2test\fP build. In many operating environments with a
sytem-installed readline library this is sufficient. However, in some
environments (e.g. if an unmodified distribution version of readline is in
use), some extra configuration may be necessary. The INSTALL file for
\fBlibreadline\fP says this:
.sp
  "Readline uses the termcap functions, but does not link with
  the termcap or curses library itself, allowing applications
  which link with readline the to choose an appropriate library."
.sp
If your environment has not been set up so that an appropriate library is
automatically included, you may need to add something like
.sp
  LIBS="-ncurses"
.sp
immediately before the \fBconfigure\fP command.
.
.
.SH "INCLUDING DEBUGGING CODE"
.rs
.sp
If you add
.sp
  --enable-debug
.sp
to the \fBconfigure\fP command, additional debugging code is included in the
build. This feature is intended for use by the PCRE2 maintainers.
.
.
.SH "DEBUGGING WITH VALGRIND SUPPORT"
.rs
.sp
If you add
.sp
  --enable-valgrind
.sp
to the \fBconfigure\fP command, PCRE2 will use valgrind annotations to mark
certain memory regions as unaddressable. This allows it to detect invalid
memory accesses, and is mostly useful for debugging PCRE2 itself.
.
.
.SH "CODE COVERAGE REPORTING"
.rs
.sp
If your C compiler is gcc, you can build a version of PCRE2 that can generate a
code coverage report for its test suite. To enable this, you must install
\fBlcov\fP version 1.6 or above. Then specify
.sp
  --enable-coverage
.sp
to the \fBconfigure\fP command and build PCRE2 in the usual way.
.P
Note that using \fBccache\fP (a caching C compiler) is incompatible with code
coverage reporting. If you have configured \fBccache\fP to run automatically
on your system, you must set the environment variable
.sp
  CCACHE_DISABLE=1
.sp
before running \fBmake\fP to build PCRE2, so that \fBccache\fP is not used.
.P
When --enable-coverage is used, the following addition targets are added to the
\fIMakefile\fP:
.sp
  make coverage
.sp
This creates a fresh coverage report for the PCRE2 test suite. It is equivalent
to running "make coverage-reset", "make coverage-baseline", "make check", and
then "make coverage-report".
.sp
  make coverage-reset
.sp
This zeroes the coverage counters, but does nothing else.
.sp
  make coverage-baseline
.sp
This captures baseline coverage information.
.sp
  make coverage-report
.sp
This creates the coverage report.
.sp
  make coverage-clean-report
.sp
This removes the generated coverage report without cleaning the coverage data
itself.
.sp
  make coverage-clean-data
.sp
This removes the captured coverage data without removing the coverage files
created at compile time (*.gcno).
.sp
  make coverage-clean
.sp
This cleans all coverage data including the generated coverage report. For more
information about code coverage, see the \fBgcov\fP and \fBlcov\fP
documentation.
.
.
.SH "SEE ALSO"
.rs
.sp
\fBpcre2api\fP(3), \fBpcre2-config\fP(3).
.
.
.SH AUTHOR
.rs
.sp
.nf
Philip Hazel
University Computing Service
Cambridge, England.
.fi
.
.
.SH REVISION
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.nf
Last updated: 07 October 2016
Copyright (c) 1997-2016 University of Cambridge.
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