Re^2: uninitialized value $

Are you saying that STDIN is getting opened and closed every time a line is read? I guess that would explain why there is nothing there. :) How about a small variation where I need to print something (a prompt or line number) on the terminal before reading the line (so I couldn't have <> in the loop control)? The (broken) code would be something like:

while ()
    {
    print $foo;
    <>;
    last unless /\S/;
    print FILE;
    }
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Re^3: uninitialized value $_ by Paladin (Vicar) on Mar 28, 2016 at 17:16 UTC
`<>;` just reads a line and throws it away. Perhaps you meant `$_ = <>;`?	[reply] [d/l] [select]
Re^4: uninitialized value $_ by Anonymous Monk on Mar 28, 2016 at 18:42 UTC
That works. I thought (incorrectly obviously) that $_ automatically was assigned the last line read. I recall seeing examples like that, but maybe it was only for reading from files.	[reply]
Re^5: uninitialized value $_ by LanX (Saint) on Mar 29, 2016 at 00:08 UTC
> $_ automatically was assigned the last line That's a special DWIM magic within the `while` condition only! `while (<>) { ... which is Perl shorthand for the more explicitly written version: ...` `while (defined($line = <ARGV>)) {` Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :) Je suis Charlie!}	[reply] [d/l] [select]
Re^6: uninitialized value $_ by soonix (Chancellor) on Mar 29, 2016 at 08:13 UTC
Re^7: uninitialized value $_ by LanX (Saint) on Mar 29, 2016 at 12:02 UTC
Re^5: uninitialized value $_ by Marshall (Canon) on Mar 28, 2016 at 22:26 UTC
Perhaps a better thought model is that $_ gets assigned the last thing read. At the end of the file, that last thing is the EOF, which is returned as undef. The fundamental problem here was poor loop design. The use of for(;;){} or while (1){} should be restricted to very special circumstances like an infinite loop in server code to wait for next connection, etc. If the loop is coded differently and I would argue properly, as corion suggests, while (<>){}, this handling undef inside the loop problem goes away.	[reply]