PCRE2SAMPLE(3)

💅 PCRE2SAMPLE(3) — like, the cutest lil intro to PCRE2 ever

okay so this is from the Library Functions Manual, and the manual page's name is literally PCRE2SAMPLE. yes bestie, we're doing the sample program page. it's giving "first day of class but make it slay" 🎀

✨ NAME ✨

PCRE2 — Perl-compatible regular expressions (revised API). that's the whole name section, short and iconic, no notes 💅

🌸 PCRE2 SAMPLE PROGRAM 🌸

so like, there's a simple, complete demonstration program to get you started with using PCRE2, and it lives in the file pcre2demo.c in the src directory in the PCRE2 distribution. a full listing of this program is given in the pcre2demo documentation. and if you don't have a copy of the PCRE2 distribution?? no stress — you can save that listing to recreate the contents of pcre2demo.c. literally copy-paste and you're in business 🫶

Here's the vibe: the demo 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. that's it, that's the whole girlboss move ✨

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. and okay, the logic is a little bit tricky because of the possibility of matching an empty string 😭 — but the comments in the code explain what is going on, so like, read them, they're your bestie here.

The code in pcre2demo.c 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. highkey important detail, don't sleep on it 🦋

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🧚 compiling it (the moment of truth)

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:

cc -o pcre2demo pcre2demo.c -lpcre2-8

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 /usr/local, you can compile the demonstration program using a command like this:

cc -o pcre2demo -I/usr/local/include pcre2demo.c \
   -L/usr/local/lib -lpcre2-8

look at that backslash doing its lil line-continuation thing. we love a formatting queen 💅

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🍓 running it (the fun part)

Once you have built the demonstration program, you can run simple tests like this:

./pcre2demo 'cat|dog' 'the cat sat on the mat'
./pcre2demo -g 'cat|dog' 'the dog sat on the cat'
./pcre2demo -i 'cat' 'the dog sat on the CAT'

cat AND dog representation, we simply stan 🐱🐶

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👑 a lil side note about pcre2test

Note that there is a much more comprehensive test program, called pcre2test, 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 pcre2demo program is provided as a relatively simple coding example. so like — pcre2test is the main character energy test suite, and pcre2demo is the chill approachable friend you learn from first. both have their moment ✨

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💀 when the linker is being dramatic

If you try to run pcre2demo when PCRE2 is not installed in the standard library directory, you may get an error like this on some operating systems (e.g. Solaris):

ld.so.1: pcre2demo: fatal: libpcre2-8.so.0: open failed: No such file or directory

This is caused by the way shared library support works on those systems. You need to add

-R/usr/local/lib

(for example) to the compile command to get round this problem.

🫶 fr fr, don't panic if you see that fatal line — it's not you, it's the shared library support on those systems being extra. just slap -R/usr/local/lib on the compile command and breathe.

🌈 AUTHOR 🌈

Philip Hazel Retired from University Computing Service Cambridge, England.

an absolute legend, we bow 🙇‍♀️👑

⭐ REVISION ⭐

Last updated: 28 February 2025 Copyright (c) 1997-2016 University of Cambridge.

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and that's the whole page, bestie!! 🎀 remember: this is PCRE2 version 10.47, and the last updated date was 28 February 2025 — so if your copy says something else, you're on a different era of the page, iykyk 💖✨🦋