Re: open(), go away with bad way, or fail with the right way?

Hello hda,

LanX has answered your question, but I was somewhat surprised by the error message (which comes courtesy of use strict;, BTW), since it appears that $fh is already declared when the die code is parsed. Deparsing shows what’s going on: or is (apparently) rewritten as unless, which places the $fh in the die clause before its declaration in the call to open:

22:56 >perl -MO=Deparse -Mstrict -we "my $file = 'x'; open (my $fh, '<
+', $file) or die qq[Can't open $fh];"
Global symbol "$fh" requires explicit package name (did you forget to 
+declare "my $fh"?) at -e line 1.
-e had compilation errors.
BEGIN { $^W = 1; }
use strict;
my $file = 'x';
die "Can't open ${'fh'}" unless open my $fh, '<', $file;

22:56 >
[download]

Hope that’s of interest,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re^2: open(), go away with bad way, or fail with the right way? by Anonymous Monk on May 31, 2019 at 14:43 UTC
Perl makes "my" variables available in the statement after the "my". This allows things like `my $foo = 'Bar'; my $foo = $foo x 2; say $foo; # 'BarBar'` [download] No, I do not defend this as a coding practice -- I'm just trying to elucidate how Perl works.	[reply] [d/l]
Re^3: open(), go away with bad way, or fail with the right way? by karlgoethebier (Abbot) on Jun 01, 2019 at 17:40 UTC
"...This allows things like..." Yes and no: `#!/usr/bin/env perl use strict; use warnings; use feature qw(say);; my $foo = 'Bar': my $foo = $foo x 2; say $foo; __END__` [download] Perl allows it generously but then it complains about `"my" variable $foo masks earlier declaration in same scope at ./foo.pl line 8.`. Iznogoud. But in a block it works flawless - no surprise: `KARL : { my $foo = $foo x 2; say $foo; }` [download] But why the effort? You could say `$foo x= 2;` which results in `BarBar`. If this is what you wanted. What i assume. Best regards, Karl ŤThe Crux of the Biscuit is the Apostropheť `perl -MCrypt::CBC -E 'say Crypt::CBC->new(-key=>'kgb',-cipher=>"Blowfish")->decrypt_hex($ENV{KARL});'`Help	[reply] [d/l] [select]
Re^4: open(), go away with bad way, or fail with the right way? by Anonymous Monk on Jun 01, 2019 at 18:00 UTC
"But why the effort?" It's only a demo. If you read the thread, it would be obvious.	[reply]
Re^5: open(), go away with bad way, or fail with the right way? by karlgoethebier (Abbot) on Jun 01, 2019 at 18:15 UTC
Re^6: open(), go away with bad way, or fail with the right way? by Anonymous Monk on Jun 01, 2019 at 20:16 UTC
Some notes below your chosen depth have not been shown here
Re^3: open(), go away with bad way, or fail with the right way? by Anonymous Monk on May 31, 2019 at 21:38 UTC
It's pretty useful in nested scopes and closures. For instance my $level = $level + 1;	[reply]
Re^2: open(), go away with bad way, or fail with the right way? by BillKSmith (Monsignor) on May 31, 2019 at 13:40 UTC
Very Strange, But if it worked the way I expect, perl would not have found the error. Bill	[reply]