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[perl #128557] Trailing space in heredoc delimiter

From:
Ed Avis
Date:
July 6, 2016 13:51
Subject:
[perl #128557] Trailing space in heredoc delimiter
Message ID:
rt-4.0.18-27239-1467813048-468.128557-75-0@perl.org
# New Ticket Created by  "Ed Avis" 
# Please include the string:  [perl #128557]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=128557 >



This is a bug report for perl from eda@waniasset.com,
generated with the help of perlbug 1.40 running under perl 5.22.2.


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

The end marker for a here-document must be the exact string, without
trailing spaces.  If the heredoc begins with <<END but instead of
'END' you have 'END ', Perl treats that as part of the quoted string
without warning.

I appreciate that this is done to be consistent with Unix tradition.
The Unix shell likewise requires an exact line with the terminator
string and no trailing space.  However, I suggest that in this day and
age it may be worth a small break with tradition in order to catch the
mistake of a trailing space after the terminator.

Firstly, many commonly used text editors do not show any visual
difference between a line with trailing space and one without, so two
programs which look identical end up with different behaviour.

Secondly, we can no longer assume that Perl programmers are familiar
with the dark arts of Unix shell scripting, so they will not know
about this 'gotcha'.

Thirdly, Perl has already broken with the behaviour of the shell in
the case of a carriage-return character.  A trailing carriage return
after the heredoc terminator is silently ignored, even on platforms
where text files use just a newline character for end of line.  The
Unix shell does not do this (or at least GNU bash doesn't).  Given
that we have already broken with the classical shell heredoc behaviour
for one kind of whitespace character, why not for others?

In my personal opinion the right fix would be to add a deprecation
warning when the heredoc terminator is seen followed by whitespace and
end-of-line.  'In future Perl versions this will be treated as the end
of the heredoc.'  Then that change can indeed be made after a release
cycle or two.

An alternative would be to simply add a warning when the heredoc
terminator appears but has whitespace after it.  Although I appreciate
the comments that heredocs are intended to be unrestricted with
'anything' appearing in them, I feel the case for a warning is even
stronger here given the invisibilty of the trailing space characters.

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=core
    severity=low
---
Site configuration information for perl 5.22.2:

Configured by Red Hat, Inc. at Mon Jun 13 12:25:51 UTC 2016.

Summary of my perl5 (revision 5 version 22 subversion 2) configuration:
   
  Platform:
    osname=linux, osvers=4.4.9-300.fc23.x86_64, archname=x86_64-linux-thread-multi
    uname='linux buildvm-14.phx2.fedoraproject.org 4.4.9-300.fc23.x86_64 #1 smp wed may 4 23:56:27 utc 2016 x86_64 x86_64 x86_64 gnulinux '
    config_args='-des -Doptimize=none -Dccflags=-O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches  -m64 -mtune=generic -Dldflags=-Wl,-z,relro  -Dccdlflags=-Wl,--enable-new-dtags -Wl,-z,relro  -Dlddlflags=-shared -Wl,-z,relro  -Dshrpdir=/usr/lib64 -DDEBUGGING=-g -Dversion=5.22.2 -Dmyhostname=localhost -Dperladmin=root@localhost -Dcc=gcc -Dcf_by=Red Hat, Inc. -Dprefix=/usr -Dvendorprefix=/usr -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl5 -Dsitearch=/usr/local/lib64/perl5 -Dprivlib=/usr/share/perl5 -Dvendorlib=/usr/share/perl5/vendor_perl -Darchlib=/usr/lib64/perl5 -Dvendorarch=/usr/lib64/perl5/vendor_perl -Darchname=x86_64-linux-thread-multi -Dlibpth=/usr/local/lib64 /lib64 /usr/lib64 -Duseshrplib -Dusethreads -Duseithreads -Dusedtrace=/usr/bin/dtrace -Duselargefiles -Dd_semctl_semun -Di_db -Ui_ndbm -Di_gdbm -Di_shadow -Di_syslog -Dman3ext=3pm -Duseperlio -Dinstallu
 srbinperl=n -Ubincompat5005 -Uversiononly -Dpager=/usr/bin/less -isr -Dd_gethostent_r_proto -Ud_endhostent_r_proto -Ud_sethostent_r_proto -Ud_endprotoent_r_proto -Ud_setprotoent_r_proto -Ud_endservent_r_proto -Ud_setservent_r_proto -Dscriptdir=/usr/bin -Dusesitecustomize'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='gcc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fwrapv -fno-strict-aliasing -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='  -g',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fwrapv -fno-strict-aliasing -I/usr/local/include'
    ccversion='', gccversion='5.3.1 20160406 (Red Hat 5.3.1-6)', gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678, doublekind=3
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16, longdblkind=3
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='gcc', ldflags ='-Wl,-z,relro  -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib64 /lib64 /usr/lib64 /usr/local/lib /usr/lib /lib/../lib64 /usr/lib/../lib64 /lib
    libs=-lpthread -lresolv -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
    perllibs=-lpthread -lresolv -lnsl -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.22.so, so=so, useshrplib=true, libperl=libperl.so
    gnulibc_version='2.22'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,--enable-new-dtags -Wl,-z,relro '
    cccdlflags='-fPIC', lddlflags='-shared -Wl,-z,relro  -L/usr/local/lib -fstack-protector-strong'

Locally applied patches:
    Fedora Patch1: Removes date check, Fedora/RHEL specific
    Fedora Patch3: support for libdir64
    Fedora Patch4: use libresolv instead of libbind
    Fedora Patch5: USE_MM_LD_RUN_PATH
    Fedora Patch6: Skip hostname tests, due to builders not being network capable
    Fedora Patch7: Dont run one io test due to random builder failures
    Fedora Patch15: Define SONAME for libperl.so
    Fedora Patch16: Install libperl.so to -Dshrpdir value
    Fedora Patch22: Document Math::BigInt::CalcEmu requires Math::BigInt (CPAN RT#85015)
    Fedora Patch26: Make *DBM_File desctructors thread-safe (RT#61912)
    Fedora Patch27: Make PadlistNAMES() lvalue again (CPAN RT#101063)
    Fedora Patch28: Make magic vtable writable as a work-around for Coro (CPAN RT#101063)
    Fedora Patch29: Fix duplicating PerlIO::encoding when spawning threads (RT#31923)
    Fedora Patch200: Link XS modules to libperl.so with EU::CBuilder on Linux
    Fedora Patch201: Link XS modules to libperl.so with EU::MM on Linux

---
@INC for perl 5.22.2:
    /home/eda/lib64/perl5/
    /usr/local/lib64/perl5
    /usr/local/share/perl5
    /usr/lib64/perl5/vendor_perl
    /usr/share/perl5/vendor_perl
    /usr/lib64/perl5
    /usr/share/perl5
    .

---
Environment for perl 5.22.2:
    HOME=/home/eda
    LANG=en_GB.UTF-8
    LANGUAGE (unset)
    LC_COLLATE=C
    LC_CTYPE=en_GB.UTF-8
    LC_MESSAGES=en_GB.UTF-8
    LC_MONETARY=en_GB.UTF-8
    LC_NUMERIC=en_GB.UTF-8
    LC_TIME=en_GB.UTF-8
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/eda/bin:/home/eda/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin:/usr/sbin:/home/eda/.local/bin:/home/eda/bin:/sbin:/usr/sbin
    PERL5LIB=/home/eda/lib64/perl5/
    PERL_BADLANG (unset)
    SHELL=/bin/bash




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