add PIRegularExpression

3rd/pcre2/doc/pcre2sample.3

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+.TH PCRE2SAMPLE 3 "14 November 2023" "PCRE2 10.45"
+.SH NAME
+PCRE2 - Perl-compatible regular expressions (revised API)
+.SH "PCRE2 SAMPLE PROGRAM"
+.rs
+.sp
+A simple, complete demonstration program to get you started with using PCRE2 is
+supplied in the file \fIpcre2demo.c\fP in the \fBsrc\fP directory in the PCRE2
+distribution. A listing of this program is given in the
+.\" HREF
+\fBpcre2demo\fP
+.\"
+documentation. If you do not have a copy of the PCRE2 distribution, you can
+save this listing to re-create the contents of \fIpcre2demo.c\fP.
+.P
+The demonstration program compiles the regular expression that is its
+first argument, and matches it against the subject string in its second
+argument. No PCRE2 options are set, and default character tables are used. If
+matching succeeds, the program outputs the portion of the subject that matched,
+together with the contents of any captured substrings.
+.P
+If the -g option is given on the command line, the program then goes on to
+check for further matches of the same regular expression in the same subject
+string. The logic is a little bit tricky because of the possibility of matching
+an empty string. Comments in the code explain what is going on.
+.P
+The code in \fBpcre2demo.c\fP is an 8-bit program that uses the PCRE2 8-bit
+library. It handles strings and characters that are stored in 8-bit code units.
+By default, one character corresponds to one code unit, but if the pattern
+starts with "(*UTF)", both it and the subject are treated as UTF-8 strings,
+where characters may occupy multiple code units.
+.P
+If PCRE2 is installed in the standard include and library directories for your
+operating system, you should be able to compile the demonstration program using
+a command like this:
+.sp
+  cc -o pcre2demo pcre2demo.c -lpcre2-8
+.sp
+If PCRE2 is installed elsewhere, you may need to add additional options to the
+command line. For example, on a Unix-like system that has PCRE2 installed in
+\fI/usr/local\fP, you can compile the demonstration program using a command
+like this:
+.sp
+.\" JOINSH
+  cc -o pcre2demo -I/usr/local/include pcre2demo.c \e
+     -L/usr/local/lib -lpcre2-8
+.sp
+Once you have built the demonstration program, you can run simple tests like
+this:
+.sp
+  ./pcre2demo 'cat|dog' 'the cat sat on the mat'
+  ./pcre2demo -g 'cat|dog' 'the dog sat on the cat'
+.sp
+Note that there is a much more comprehensive test program, called
+.\" HREF
+\fBpcre2test\fP,
+.\"
+which supports many more facilities for testing regular expressions using all
+three PCRE2 libraries (8-bit, 16-bit, and 32-bit, though not all three need be
+installed). The
+.\" HREF
+\fBpcre2demo\fP
+.\"
+program is provided as a relatively simple coding example.
+.P
+If you try to run
+.\" HREF
+\fBpcre2demo\fP
+.\"
+when PCRE2 is not installed in the standard library directory, you may get an
+error like this on some operating systems (e.g. Solaris):
+.sp
+  ld.so.1: pcre2demo: fatal: libpcre2-8.so.0: open failed: No such file or directory
+.sp
+This is caused by the way shared library support works on those systems. You
+need to add
+.sp
+  -R/usr/local/lib
+.sp
+(for example) to the compile command to get round this problem.
+.
+.
+.SH AUTHOR
+.rs
+.sp
+.nf
+Philip Hazel
+Retired from University Computing Service
+Cambridge, England.
+.fi
+.
+.
+.SH REVISION
+.rs
+.sp
+.nf
+Last updated: 14 November 2023
+Copyright (c) 1997-2016 University of Cambridge.
+.fi