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Re: Regex library
Re: Regex library
Sun, 27 Jun 2021 00:24:35 -0600
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On 2021-06-18 1:42 a.m., Pietro Paolini wrote:
In the sed source code there is a folder called lib/ which seems to include
the GNU lib and or maybe I am flay wrong and that isn't gnulib
The content of "/lib" in the sed-4.8.tar.gz is indeed a subset of gnulib.
Another question concerns the regex library in use, I can see the code
using regex functions defined as part of gnulib
Yet when I ldd the sed binary I can observe that PCRE is dynamically linked
What library is used for regex in GNU sed ? I inclined to say that PCRE
isn't used, after all libpthread gets linked too and it is not used.
You're correct - PCRE is not used by gnu sed.
On my system, it is "libselinux" which uses PCRE (and sed does use
selinux by default):
$ ldd /lib/x86_64-linux-gnu/libselinux.so.1 | grep -i pcre
libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3
As for which regex code is used, the answer is a bit nuanced.
The source code file which does the actual regex matching is "sed/regexp.c":
Inside, two main function are used: re_compile_pattern() and re_search().
These are defined in gnulib's "regcomp.c" and "regexec.c" files:
These functions are also defined in glibc (although internal).
glibc and gnulib's source code are often synchronized, so these
functions might be identical, or (if it's an old glibc) - gnulib's
version that is bundled with gnu sed might be newer.
During "./configure", if the system's glibc is detected to have new-
enough version of these functions - they will be used.
Otherwise, the gnulib version will be used.
You can force the build to use glibc's version with:
But that's not recommended, unless you are certain of what you're
To add another layer, GNU sed employs some regex optimizations using a
faster engine (gnulib's DFA engine,
That code is not available in glibc, and so it is always taken from gnulib.
Hope this answers the question.
- Regex library, Pietro Paolini, 2021/06/18
- Re: Regex library,
Assaf Gordon <=