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[perl #119191] "\c\" is a syntax error

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From:
l . mai @ web . de
Date:
August 7, 2013 14:15
Subject:
[perl #119191] "\c\" is a syntax error
Message ID:
rt-3.6.HEAD-2552-1375884893-689.119191-75-0@perl.org
# New Ticket Created by  l.mai@web.de 
# Please include the string:  [perl #119191]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org:443/rt3/Ticket/Display.html?id=119191 >



This is a bug report for perl from l.mai@web.de,
generated with the help of perlbug 1.39 running under perl 5.18.0.


-----------------------------------------------------------------
[Please describe your issue here]

% perl -we 'printf "%vd\n", "\c\"'
Can't find string terminator '"' anywhere before EOF at -e line 1.
 % perl -we 'printf "%vd\n", "\c\\"'
28.92
% perl -we 'printf "%vd\n", "\x1c\\"'
28.92

There's no way to get a CTRL-\ (0x1C) with perl's \c notation.

The obvious syntax "\c\" is a syntax error.

The next try "\c\\" parses but ends up being a 2-character string consisting of
CTRL-\ and \ (backslash).

I think the latter case is definitely a bug because the middle backslash ends
up doing double duty: it is used by \c to form \c\ (0x1C), but then also
escapes the third backslash to form \\ (0x5C). This half-reparsing shouldn't
happen.

And for consistency with other control characters it would be nice if you could
get a ^\ by writing "\c\".

(This bug may be a duplicate but when I search RT for "\c\" I get 693 pages of
no results.)

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=core
    severity=low
---
This perlbug was built using Perl 5.12.1 - Thu Jun  3 20:09:15 CEST 2010
It is being executed now by  Perl 5.18.0 - Fri May 24 23:20:48 CEST 2013.

Site configuration information for perl 5.18.0:

Configured by mauke at Fri May 24 23:20:48 CEST 2013.

Summary of my perl5 (revision 5 version 18 subversion 0) configuration:
   
  Platform:
    osname=linux, osvers=3.5.7-gentoo, archname=i686-linux
    uname='linux nora 3.5.7-gentoo #5 preempt sat jan 26 16:46:10 cet 2013 i686 amd athlon(tm) 64 processor 3200+ authenticamd gnulinux '
    config_args=''
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=undef, usemultiplicity=undef
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=undef, use64bitall=undef, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2 -flto',
    cppflags='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.8.0', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='cc', ldflags ='-fstack-protector -L/usr/local/lib -O2 -flto'
    libpth=/usr/local/lib /lib/../lib /usr/lib/../lib /lib /usr/lib
    libs=-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
    perllibs=-lnsl -ldl -lm -lcrypt -lutil -lc
    libc=/lib/libc-2.15.so, so=so, useshrplib=false, libperl=libperl.a
    gnulibc_version='2.15'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -flto -L/usr/local/lib -fstack-protector'

Locally applied patches:
    SAVEARGV0 - disable magic open in <ARGV>

---
@INC for perl 5.18.0:
    /home/mauke/usr/local/lib/perl5/site_perl/5.18.0/i686-linux
    /home/mauke/usr/local/lib/perl5/site_perl/5.18.0
    /home/mauke/usr/local/lib/perl5/5.18.0/i686-linux
    /home/mauke/usr/local/lib/perl5/5.18.0
    .

---
Environment for perl 5.18.0:
    HOME=/home/mauke
    LANG=en_US.UTF-8
    LANGUAGE (unset)
    LC_COLLATE=POSIX
    LD_LIBRARY_PATH=/home/mauke/usr/local/lib
    LOGDIR (unset)
    PATH=/home/mauke/usr/perlbrew/bin:/home/mauke/usr/local/bin:/usr/local/bin:/usr/bin:/bin:/opt/bin:/usr/i686-pc-linux-gnu/gcc-bin/4.6.3:/opt/sun-jdk-1.4.2.13/bin:/opt/sun-jdk-1.4.2.13/jre/bin:/opt/sun-jdk-1.4.2.13/jre/javaws:/opt/dmd/bin:/usr/games/bin
    PERLBREW_BASHRC_VERSION=0.43
    PERLBREW_HOME=/home/mauke/.perlbrew
    PERLBREW_PATH=/home/mauke/usr/perlbrew/bin
    PERLBREW_ROOT=/home/mauke/usr/perlbrew
    PERLBREW_VERSION=0.27
    PERL_BADLANG (unset)
    PERL_UNICODE=SAL
    SHELL=/bin/bash


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