in reply to Scope of $/

Limit the scope of the changed value of $/, by "local"izing it, and enclosing it in the smallest block possible: 
{ # Add an enclosing block
   local $/= "\n\n\n";
   while(<>){
      local $/="\n"; # Reset to normal behaviour inside loop only
      my ($filename)=/^(\S+)/;
      my $text=reader::firstline($filename);
   }
} # End enclosing block.

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This code avoids "Action at a distance", by making wierd settings in as limited a scope as possible.

        This is not an optical illusion, it just looks like one.

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Re^2: Scope of $/
by BillKSmith (Monsignor) on May 26, 2016 at 13:29 UTC
    A truly minimal scope solves the problem. 
    use strict;
use reader;
#$/= "\n\n\n";
while(do{local $/="\n\n\n"; $_=<>}){
    my ($filename)=/^(\S+)/;
    my $text=reader::firstline($filename);
}

    [download]

    Update: Commented out original definition of $/.

    Bill
[reply]
[d/l]
      Applause, for a truly elegant solution !

      I wish I had thought of that.

              This is not an optical illusion, it just looks like one.

[reply]
Re^2: Scope of $/
by Anonymous Monk on May 26, 2016 at 01:23 UTC

    The enclosing block is just noise :) unless you give it a name

[reply]
      That is not true. No name is required. The {} set the scope of the local. For my demo below, I used an "our" variable, package scope. A Perl Global like $/ acts similar. You cannot localize a "my" variable.

      I guess you can think of a local var as sort of like creating a stack of that variable. The local statement is like a "push" and when you exit the scope of the local, that is like a "pop". Rough analogy, but that is descriptive of the behavior. 

      #!usr/bin/perl
use warnings;
use strict;


our $x = 1;  #a package variable

{
   print "$x\n";  #prints 1
   local $x = 99;
   print "$x\n";  #prints 99
}

print "$x\n";  #prints 1, back to before the "local"

      [download]
[reply]
[d/l]

        :) in the OPs program, having  { local $/ ... } on the outside doesn't change the behavior of the program,

        therefore no benefit is realized ... so the extra {local} is just extra typing (noise),

        unless you add a name, like  sub StdinTriElReader{ local $/ = "\n\n\n"; ... } then its serves a purpose

        :D:D:)

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