From hseuming@cs.nyu.edu

Dear fellow Perl lovers,

The Perl version i use is 5.8.6 on Linux, Mac OS X,
and Sun Solaris 8.

The following self-contained program dies with a
"read failed" message​:

  #!/usr/local/bin/perl -w

  use strict;

  my $s = <<'EOF';
  line A
  line B
  a third line
  EOF

  open (F, '<', \$s)
  or die "Could not open string as a file";
  local $/ = "";
  my $ln = <F>;
  die "read failed" unless defined $ln;
  close F;

However, if I have it read from a file with the
same contents as $s instead of $s itself, it
succeeds. To wit​:

  #!/usr/local/bin/perl -w

  use strict;

  my $s = <<'EOF';
  line A
  line B
  a third line
  EOF

  open (F, '>', "/var/tmp/Z");
  print F $s;
  close F;

  open (F, '<', "/var/tmp/Z")
  or die "Could not open string as a file";
  local $/ = "";
  my $ln = <F>;
  die "read failed" unless defined $ln;
  close F;

This looks like a bona-fide Perl bug. Am I
missing something?

Note that reading from them works fine as long
as I don't touch $/.

-- Hseuming

Emails :​: hseuming.chen@​citigroup.com hseuming@​cs.nyu.edu
  hseuming@​gnu.mit.edu hseuming@​yahoo.com
  hseuming@​gmail.com hseuming@​hotmail.com

Phones :​: (908)563-0029 (o) (973)597-1801 (h)
--------------------------------------------------------------_

From @schwern

On Sun, May 22, 2005 at 06​:09​:41AM -0000, Hseu-Ming Chen wrote​:

The following self-contained program dies with a
"read failed" message​:

#!/usr/local/bin/perl -w

use strict;

my $s = <<'EOF';
line A
line B
a third line
EOF

open (F, '<', \$s)
or die "Could not open string as a file";
local $/ = "";
my $ln = <F>;
die "read failed" unless defined $ln;
close F;

Note that reading from them works fine as long
as I don't touch $/.

Yeah, I can repeat this bug and confirm that "local $/ = ''"; is the
problem. Interestingly, "local $/;" works as does "local $/ = undef;".

--
Michael G Schwern schwern@​pobox.com http​://www.pobox.com/~schwern
Don't try the paranormal until you know what's normal.
  -- "Lords and Ladies" by Terry Prachett

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

From @rgarcia

On 22 May 2005 06​:09​:41 -0000, via RT Hseu-Ming Chen
<perlbug-followup@​perl.org> wrote​:

The following self-contained program dies with a
"read failed" message​:

#!/usr/local/bin/perl -w

use strict;

my $s = <<'EOF';
line A
line B
a third line
EOF

open (F, '<', \$s)
or die "Could not open string as a file";
local $/ = "";
my $ln = <F>;
die "read failed" unless defined $ln;
close F;

The bug is in PerlIOScalar_unread, which doesn't do what it should.
The following patch solves this particular problem, but it's obviously
not sufficient... it's late and I'll try to work out a proper solution
another day.

==== //depot/perl/ext/PerlIO/scalar/scalar.xs#12 -
/opt/bleadperl/p4/perl/ext/PerlIO/scalar/scalar.xs ====
--- /home/rafael/tmp/tmp.21342.0 2005-05-23 00​:36​:44.351368184 +0200
+++ /opt/bleadperl/p4/perl/ext/PerlIO/scalar/scalar.xs 2005-05-23
00​:36​:37.732374424 +0200
@​@​ -105,11 +105,7 @​@​ SSize_t
PerlIOScalar_unread(pTHX_ PerlIO * f, const void *vbuf, Size_t count)
{
  PerlIOScalar *s = PerlIOSelf(f, PerlIOScalar);
- char *dst = SvGROW(s->var, (STRLEN)s->posn + count);
- Move(vbuf, dst + s->posn, count, char);
- s->posn += count;
- SvCUR_set(s->var, (STRLEN)s->posn);
- SvPOK_on(s->var);
+ s->posn -= count;
  return count;
}

From @rgarcia

On 5/23/05, Rafael Garcia-Suarez <rgarciasuarez@​gmail.com> wrote​:

The bug is in PerlIOScalar_unread, which doesn't do what it should.
The following patch solves this particular problem, but it's obviously
not sufficient... it's late and I'll try to work out a proper solution
another day.

Now hopefully implemented in bleadperl as :

Change 24543 on 2005/05/23 by rgs@​marais

  Fix [perl #35929] : PerlIO​::scalar didn't understand $/ = ""
  because PerlIOScalar_unread was broken.
  Bump version number of PerlIO​::scalar to 0.04.

@rgs - Status changed from 'open' to 'resolved'