From @ysth

Created by @ysth

This is properly an endless loop, since the change to $1 in the continue
block is scoped to just that block​:

$ perl -wle'$^O=/(.*)/; while ($1) { print $1 } continue { $1=/.(.*)/ }'
linux
linux
linux
...

but that isn't the case in the supposedly equivalent for loop​:

$ perl -wle'$^O=/(.*)/; for (;$1;$1=/.(.*)/) { print $1 }'
linux
inux
nux
ux
x

Flags:
    category=core
    severity=low

Site configuration information for perl v5.8.8:

Configured by Debian Project at Tue Nov 27 10:56:10 GMT 2007.

Summary of my perl5 (revision 5 version 8 subversion 8) configuration:
  Platform:
    osname=linux, osvers=2.6.15.7, archname=i486-linux-gnu-thread-multi
    uname='linux palmer 2.6.15.7 #1 smp thu sep 7 19:42:20 utc 2006 i686
gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN
-Dcccdlflags=-fPIC -Darchname=i486-linux-gnu -Dprefix=/usr
-Dprivlib=/usr/share/perl/5.8 -Darchlib=/usr/lib/perl/5.8
-Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5
-Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local
-Dsitelib=/usr/local/share/perl/5.8.8
-Dsitearch=/usr/local/lib/perl/5.8.8 -Dman1dir=/usr/share/man/man1
-Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1
-Dsiteman3dir=/usr/local/man/man3 -Dman1ext=1 -Dman3ext=3perl
-Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Ud_ualarm -Uusesfio
-Uusenm -Duseshrplib -Dlibperl=libperl.so.5.8.8 -Dd_dosuid -des'
    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 ='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS
-DDEBIAN -fno-strict-aliasing -pipe -I/usr/local/include
-D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS -DDEBIAN
-fno-strict-aliasing -pipe -I/usr/local/include'
    ccversion='', gccversion='4.2.3 20071123 (prerelease) (Ubuntu
4.2.2-3ubuntu4)', 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 =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=/lib/libc-2.6.1.so, so=so, useshrplib=true, libperl=libperl.so.5.8.8
    gnulibc_version='2.6.1'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib'

Locally applied patches:



@INC for perl v5.8.8:
    /etc/perl
    /usr/local/lib/perl/5.8.8
    /usr/local/share/perl/5.8.8
    /usr/lib/perl5
    /usr/share/perl5
    /usr/lib/perl/5.8
    /usr/share/perl/5.8
    /usr/local/lib/site_perl
    .


Environment for perl v5.8.8:
    HOME=/home/ysth
    LANG=en_US.UTF-8
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/ysth/bin:/home/ysth/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
    PERL_BADLANG (unset)
    SHELL=/bin/bash

From @jkeenan

On Sun Nov 30 00​:14​:04 2008, ysth wrote​:

This is a bug report for perl from sthoenna@​efn.org,
generated with the help of perlbug 1.35 running under perl v5.8.8.

-----------------------------------------------------------------
[Please enter your report here]

This is properly an endless loop, since the change to $1 in the
continue
block is scoped to just that block​:

$ perl -wle'$^O=/(.*)/; while ($1) { print $1 } continue {
$1=/.(.*)/ }'
linux
linux
linux
...

but that isn't the case in the supposedly equivalent for loop​:

$ perl -wle'$^O=/(.*)/; for (;$1;$1=/.(.*)/) { print $1 }'
linux
inux
nux
ux
x

Is there a real bug here? Or is it really a case of imprecise
documentation leading to inaccurate expectations?

I can confirm that in the while...continue case, the change to $1 is
scoped to the continue block​:

#####
$ perl -wle'$^O=/(.*)/; while ($1) { print $1 } continue { $1=/.(.*)/;
print "x​: $1" }'
darwin
x​: arwin
darwin
x​: arwin
...
#####

However, when I call 'perldoc -f continue', I find no discussion of
scoping issues within the continue block.

The relevant documentation of for loops is found in 'perldoc perlsyn'​:

#####
  For Loops
  Perl's C-style "for" loop works like the corresponding "while"
loop; that means that this​:

  for ($i = 1; $i < 10; $i++) {
  ...
  }

  is the same as this​:

  $i = 1;
  while ($i < 10) {
  ...
  } continue {
  $i++;
  }
#####

Would it suffice to clarify the 'perlfunc' documentation of scoping in
the continue block, and then add a caveat to the documentation of for
loops in 'perlsyn'?

Thank you very much.
Jim Keenan

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

From @ysth

This isn't anything special about continue blocks; $1 and friends are
dynamically scoped in *any* block as if there were a `local $1 = $1;` at
the beginning (that is, their values propagate nest-in-ward but not
nest-out-ward).

Adding a caveat to the for loop documentation would probably not be as good
as just saying "nearly the same as this".

On Sat, Nov 10, 2012 at 5​:48 AM, James E Keenan via RT <
perlbug-followup@​perl.org> wrote​:

On Sun Nov 30 00​:14​:04 2008, ysth wrote​:

This is a bug report for perl from sthoenna@​efn.org,
generated with the help of perlbug 1.35 running under perl v5.8.8.

-----------------------------------------------------------------
[Please enter your report here]

This is properly an endless loop, since the change to $1 in the
continue
block is scoped to just that block​:

$ perl -wle'$^O=/(.*)/; while ($1) { print $1 } continue {
$1=/.(.*)/ }'
linux
linux
linux
...

but that isn't the case in the supposedly equivalent for loop​:

$ perl -wle'$^O=/(.*)/; for (;$1;$1=/.(.*)/) { print $1 }'
linux
inux
nux
ux
x

Is there a real bug here? Or is it really a case of imprecise
documentation leading to inaccurate expectations?

I can confirm that in the while...continue case, the change to $1 is
scoped to the continue block​:

#####
$ perl -wle'$^O=/(.*)/; while ($1) { print $1 } continue { $1=/.(.*)/;
print "x​: $1" }'
darwin
x​: arwin
darwin
x​: arwin
...
#####

However, when I call 'perldoc -f continue', I find no discussion of
scoping issues within the continue block.

The relevant documentation of for loops is found in 'perldoc perlsyn'​:

#####
For Loops
Perl's C-style "for" loop works like the corresponding "while"
loop; that means that this​:

       for \($i = 1; $i \< 10; $i\+\+\) \{
           \.\.\.
       \}

   is the same as this&#8203;:

       $i = 1;
       while \($i \< 10\) \{
           \.\.\.
       \} continue \{
           $i\+\+;
       \}

#####

Would it suffice to clarify the 'perlfunc' documentation of scoping in
the continue block, and then add a caveat to the documentation of for
loops in 'perlsyn'?

Thank you very much.
Jim Keenan