in reply to Re^3: How to localize conditionally? (tias)
in thread How to localize conditionally?

No, but how can one assign to a hash element that does not exist? Well, %ENV is magical, so let's test it out. 

$ perl -wE'
   my $condition = 0;
   say exists($ENV{BLAH}) || 0;
   local $ENV{BLAH} = $condition ? 42 : $ENV{BLAH};
   say exists($ENV{BLAH}) || 0;
'
0
1

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So I was right 

This is perl 5, version 12, subversion 2 (v5.12.2) built for i686-linu
+x

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Re^5: How to localize conditionally? (tias)
by tye (Sage) on Mar 14, 2011 at 16:18 UTC

    My tests appeared to work for strange reasons. Sorry about that. But you can fix the original without copying the whole environment: 

        local $ENV{BLAH};
    if(  @ARGV  ) {
        $ENV{BLAH}= 42;
    } else {
        delete $ENV{BLAH};
    }

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    - tye        

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