From @rjbs

Created by @rjbs

We closed #121085, but it ended by noting this problem​:

  use warnings;

  my $filename = qq{does-not-exist\n};
  open my $fh, "< $filename" or warn "failed to open​: $!";

The above program warns​:

  Unsuccessful open on filename containing newline at program line 5.
  failed to open​: No such file or directory at program line 5.

Two-arg open trims whitespace from the filename, so the filename being
opened does not have a newline in it. The warning is misleading.
If we `touch does-not-exist`, the program runs without warnings, because
the newline is never part of the path being addressed. perl should
only warn when the \n has not been stripped before the open call.

Flags:
    category=core
    severity=low

Site configuration information for perl 5.23.3:

Configured by rjbs at Mon Sep 21 11:54:00 EDT 2015.

Summary of my perl5 (revision 5 version 23 subversion 3) configuration:
   
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    libpth=/usr/local/lib /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/7.0.0/lib /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib /usr/lib /opt/local/lib
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@INC for perl 5.23.3:
    /Users/rjbs/.plenv/versions/23.3/lib/perl5/site_perl/5.23.3/darwin-2level
    /Users/rjbs/.plenv/versions/23.3/lib/perl5/site_perl/5.23.3
    /Users/rjbs/.plenv/versions/23.3/lib/perl5/5.23.3/darwin-2level
    /Users/rjbs/.plenv/versions/23.3/lib/perl5/5.23.3
    .


Environment for perl 5.23.3:
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    HOME=/Users/rjbs
    LANG=en_US.UTF-8
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
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    PERLDOC=-otext
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    PERL_MAILERS=sendmail:/Users/rjbs/bin/sendmail
    SHELL=/opt/local/bin/zsh

From @wolfsage

On Fri Nov 06 07​:11​:34 2015, rjbs wrote​:

use warnings;

my $filename = qq{does-not-exist\n};
open my $fh, "< $filename" or warn "failed to open​: $!";

The above program warns​:

Unsuccessful open on filename containing newline at program line 5.
failed to open​: No such file or directory at program line 5.

Shouldn't this warn?

use warnings;

my $filename = qq{does-not-exist\n};
open my $fh, "<", " $filename" or warn "failed to open​: $!";

Also, why does 2-arg-open strip \n and 3-arg-open not?

Is this documented somewhere? Shouldn't these behave the same?

-- Matthew Horsfall (alh)

From [Unknown Contact. See original ticket]

On Fri Nov 06 07​:11​:34 2015, rjbs wrote​:

use warnings;

my $filename = qq{does-not-exist\n};
open my $fh, "< $filename" or warn "failed to open​: $!";

The above program warns​:

Unsuccessful open on filename containing newline at program line 5.
failed to open​: No such file or directory at program line 5.

Shouldn't this warn?

use warnings;

my $filename = qq{does-not-exist\n};
open my $fh, "<", " $filename" or warn "failed to open​: $!";

Also, why does 2-arg-open strip \n and 3-arg-open not?

Is this documented somewhere? Shouldn't these behave the same?

-- Matthew Horsfall (alh)

From @ap

* Matthew Horsfall via RT <perlbug-comment@​perl.org> [2016-01-16 18​:50]​:

Shouldn't this warn?

use warnings;

my $filename = qq{does-not-exist\n};
open my $fh, "<", " $filename" or warn "failed to open​: $!";

Yes it absolutely should.

So the behaviours must flip – the 2-arg open does warn but ought not
while the 3-arg open doesn’t warn but ought to.

Also, why does 2-arg-open strip \n and 3-arg-open not?

Is this documented somewhere? Shouldn't these behave the same?

No they should absolutely not. It is documented right in perlfunc​:

  The filename passed to the one- and two-argument forms of open()
  will have leading and trailing whitespace deleted and normal
  redirection characters honored.

This very fact was the raison d’être for 3-arg open in the first place.
2-arg open has always been this way and could not be changed, but this
behaviour had to be fixed, so 3-arg open was added as an interface which
doesn’t do that.

Regards,
--
Aristotle Pagaltzis // <http​://plasmasturm.org/>

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

From @wolfsage

On Sun, Jan 17, 2016 at 10​:59 PM, Aristotle Pagaltzis <pagaltzis@​gmx.de> wrote​:

So the behaviours must flip – the 2-arg open does warn but ought not
while the 3-arg open doesn’t warn but ought to.

Hmm, it seems strange that we no longer want to warn on 2-arg open.

If a user does this intentionally​:

  open(my $fh, "<somefile\n");

it will fail and may surprise them that it didn't work....

Regardless, thanks for the explanation.

A possible fix is at
http​://perl5.git.perl.org/perl.git/commitdiff/ab3be07ebaf7e0b17d0482e6a74e69074f0f6e33.

-- Matthew Horsfall (alh)