From cdl@genome.stanford.edu

This is a bug report for perl from cdl@​best.com,
generated with the help of perlbug 1.35 running under perl v5.8.6.

The following prints "yes" (ie. works)

perl -we 'print(("a" =~ m/\C/) ? "yes" : "no", "\n")'

But this (added [] around \C) prints a warning and doesn't work
(prints "no")

perl -we 'print(("a" =~ m/[\C]/) ? "yes" : "no", "\n")'
Unrecognized escape \C in character class passed through in regex;
marked by <-- HERE in m/[\C <-- HERE ]/ at -e line 1.

I tested this with and without 'use charnames'
This also appears to be the case with \X
This also appears to be the case under Perl 5.8.8

I've no personal need for this to be fixed, I'm simply trying to
characterize in a technical note which character class abbreviations
work inside m/[]/ and which do not. These two seem inconsistent with
the rest. So, a simple confirmation that this is a bug or a
misunderstanding on my part is sufficient. Thank you!

Flags​:
  category=core
  severity=low

Site configuration information for perl v5.8.6​:

Configured by root at Thu Nov 2 10​:35​:22 PST 2006.

Summary of my perl5 (revision 5 version 8 subversion 6) configuration​:
  Platform​:
  osname=darwin, osvers=8.0, archname=darwin-thread-multi-2level
  uname='darwin b07.apple.com 8.0 darwin kernel version 8.3.0​: mon
oct 3 20​:04​:04 pdt 2005; root​:xnu-792.6.22.obj~2release_ppc power
macintosh powerpc '
  config_args='-ds -e -Dprefix=/usr -Dccflags=-g -pipe -
Dldflags=-Dman3ext=3pm -Duseithreads -Duseshrplib'
  hint=recommended, useposix=true, d_sigaction=define
  usethreads=define use5005threads=undef useithreads=define
usemultiplicity=define
  useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
  use64bitint=undef use64bitall=undef uselongdouble=undef
  usemymalloc=n, bincompat5005=undef
  Compiler​:
  cc='cc', ccflags ='-g -pipe -fno-common -DPERL_DARWIN -no-cpp-
precomp -fno-strict-aliasing -I/usr/local/include',
  optimize='-Os',
  cppflags='-no-cpp-precomp -g -pipe -fno-common -DPERL_DARWIN -no-
cpp-precomp -fno-strict-aliasing -I/usr/local/include'
  ccversion='', gccversion='3.3 20030304 (Apple Computer, Inc.
build 1819)', gccosandvers=''
  intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=4321
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=8
  ivtype='long', ivsize=4, nvtype='double', nvsize=8,
Off_t='off_t', lseeksize=8
  alignbytes=8, prototype=define
  Linker and Libraries​:
  ld='env MACOSX_DEPLOYMENT_TARGET=10.3 cc', ldflags ='-L/usr/
local/lib'
  libpth=/usr/local/lib /usr/lib
  libs=-ldbm -ldl -lm -lc
  perllibs=-ldl -lm -lc
  libc=/usr/lib/libc.dylib, so=dylib, useshrplib=true,
libperl=libperl.dylib
  gnulibc_version=''
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=bundle, d_dlsymun=undef, ccdlflags=' '
  cccdlflags=' ', lddlflags='-bundle -undefined dynamic_lookup -L/
usr/local/lib'

Locally applied patches​:
  23953 - fix for File​::Path​::rmtree CAN-2004-0452 security issue
  33990 - fix for setuid perl security issues
  SPRINTF0 - fixes for sprintf formatting issues - CVE-2005-3962

@​INC for perl v5.8.6​:
  /sw/lib/perl5/5.8.6/darwin-thread-multi-2level
  /sw/lib/perl5/5.8.6
  /sw/lib/perl5
  /sw/lib/perl5/darwin
  /System/Library/Perl/5.8.6/darwin-thread-multi-2level
  /System/Library/Perl/5.8.6
  /Library/Perl/5.8.6/darwin-thread-multi-2level
  /Library/Perl/5.8.6
  /Library/Perl
  /Network/Library/Perl/5.8.6/darwin-thread-multi-2level
  /Network/Library/Perl/5.8.6
  /Network/Library/Perl
  /System/Library/Perl/Extras/5.8.6/darwin-thread-multi-2level
  /System/Library/Perl/Extras/5.8.6
  /Library/Perl/5.8.1
  .

Environment for perl v5.8.6​:
  DYLD_LIBRARY_PATH (unset)
  HOME=/Volumes/Users HD/cdl
  LANG (unset)
  LANGUAGE (unset)
  LD_LIBRARY_PATH (unset)
  LOGDIR (unset)
  PATH=/sw/bin​:/sw/sbin​:.​:/Users/cdl/bin​:/usr/bin​:/bin​:/usr/local/
bin​:/sbin​:/usr/sbin​:/etc​:/opt/local/bin​:/opt/local/sbin​:/usr/X11R6/bin
  PERL5LIB=/sw/lib/perl5​:/sw/lib/perl5/darwin
  PERL_BADLANG (unset)
  SHELL=/bin/csh

From @rgarcia

On 19/03/07, via RT Christopher Lane <perlbug-followup@​perl.org> wrote​:

The following prints "yes" (ie. works)

perl -we 'print(("a" =~ m/\C/) ? "yes" : "no", "\n")'

But this (added [] around \C) prints a warning and doesn't work
(prints "no")

perl -we 'print(("a" =~ m/[\C]/) ? "yes" : "no", "\n")'
Unrecognized escape \C in character class passed through in regex;
marked by <-- HERE in m/[\C <-- HERE ]/ at -e line 1.

I tested this with and without 'use charnames'
This also appears to be the case with \X

I'm not sure that \C or \X would be useful, or would even make sense,
in character classes. But that doesn't seem to be documented in
perlre.

The RT System itself - Status changed from 'new' to 'open'

From @khwilliamson

Thanks for submitting this report. However, it has been overtaken by events. The decision has been made to remove \C entirely. (This was supposed to be done for 5.24, but slipped through the cracks, so will be done in 5.26) So there is no need to document something that is about to go away.
--
Karl Williamson

@khwilliamson - Status changed from 'open' to 'rejected'

From @khwilliamson

On 03/10/2016 11​:01 AM, Karl Williamson via RT wrote​:

Thanks for submitting this report. However, it has been overtaken by events. The decision has been made to remove \C entirely. (This was supposed to be done for 5.24, but slipped through the cracks, so will be done in 5.26) So there is no need to document something that is about to go away.

I should have been clearer. The ticket wasn't actually proposing that
\C be added to bracketed character classes. As the response indicated,
that doesn't really make sense. But rather that we document that it
doesn't work in those classes. No one bothered to do this, and now
there is no point to doing so, as it is about to become a syntax error,
and we don't want to encourage its use in any way.