POSIX::strerror() clears $!

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Migrated from rt.perl.org#126229 (status was 'resolved')

Searchable as RT126229$

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From zhouzhen1@gmail.com

I found that POSIX​::strerror() clears $!. For example,

perl -MPOSIX -e '$! = 29; strerror($!); print $!, "\n"';

prints nothing to terminal under Perl 5.22.0, 5.20.1, 5.14.2. However, it
is able to print "Illegal seek" under 5.8.8 and 5.10.1. So it is likely to
have broken since some time between 5.10 and 5.14 (, not tested 5.12
though).

And this is probably not an issue in POSIX itself. I looked at
POSIX​::strerror source, and further found that the issue demo can also be
like below,

perl -e '$! = 29; sub { local $! = $_[0]; }->($!); print "$!\n";'

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From @iabyn

On Wed, Sep 30, 2015 at 08​:59​:32PM -0700, Zhenyi Zhou wrote​:

I found that POSIX​::strerror() clears $!. For example,

perl -MPOSIX -e '$! = 29; strerror($!); print $!, "\n"';

prints nothing to terminal under Perl 5.22.0, 5.20.1, 5.14.2. However, it
is able to print "Illegal seek" under 5.8.8 and 5.10.1. So it is likely to
have broken since some time between 5.10 and 5.14 (, not tested 5.12
though).

And this is probably not an issue in POSIX itself. I looked at
POSIX​::strerror source, and further found that the issue demo can also be
like below,

perl -e '$! = 29; sub { local $! = $_[0]; }->($!); print "$!\n";'

This can be reduced to

  $! = 29;
  { local $! = $! }
  print "[$!]\n"; # prints "[]"

Its a messy interaction between local() and magic vars. I'm not sure it can
be fixed. Of course the specific issue of strerror() is capable of being
fixed, by avoiding the equivalent of local $! = $!.

--
Music lesson​: a symbiotic relationship whereby a pupil's embellishments
concerning the amount of practice performed since the last lesson are
rewarded with embellishments from the teacher concerning the pupil's
progress over the corresponding period.

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

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From @iabyn

On Thu, Oct 01, 2015 at 11​:30​:57AM +0100, Dave Mitchell wrote​:

This can be reduced to

$\! = 29;
\{ local $\! = $\! \}
print "\[$\!\]\\n"; \# prints "\[\]"

Its a messy interaction between local() and magic vars. I'm not sure it can
be fixed.

Of course the specific issue of strerror() is capable of being
fixed, by avoiding the equivalent of local $! = $!.

And that's now fixed in bleadperl by commit 068e3fb.

--
No man treats a motor car as foolishly as he treats another human being.
When the car will not go, he does not attribute its annoying behaviour to
sin, he does not say, You are a wicked motorcar, and I shall not give you
any more petrol until you go. He attempts to find out what is wrong and
set it right.
  -- Bertrand Russell,
  Has Religion Made Useful Contributions to Civilization?

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@iabyn - Status changed from 'open' to 'pending release'

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From @khwilliamson

Thank you for submitting this report. You have helped make Perl better.
 
With the release of Perl 5.24.0 on May 9, 2016, this and 149 other issues have been resolved.

Perl 5.24.0 may be downloaded via https://metacpan.org/release/RJBS/perl-5.24.0

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@khwilliamson - Status changed from 'pending release' to 'resolved'