Hmm, this hangs when reading STDIN; got whatever never gets printed.

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

print STDOUT "stuff\n";
my $whatever = <STDIN>;
print "got whatever: $whatever";

exit;
[download]

I'm not too sure why it hangs: it seems to be that STDIN actually isn't tied to STDOUT, as you think it is. For example, we can prevent the above code from hanging forever by playing with alarm:

#!/usr/bin/perl

use strict;
use warnings;

$SIG{ALRM} = sub { die };

print STDOUT "whatever\n";
my $in;

eval {
  alarm 1;
  chomp ( $in = <STDIN> );
  alarm 0;
}; 

print "got in: $in\n";
[download]

result:

whatever
Use of uninitialized value in concatenation (.) or string at foo.pl li
+ne 17.
got in:
[download]

1. The first line, "whatever", is us printing to STDOUT.
2. Next we get a warning about an uninitialized value - this is the warnings pragma in action, helpfully telling us that we're trying to print something that hasn't been set yet.
3. Finally, there's a "got in: " line where we expect to see "got in: whatever".

So - what this means is that printing to STDOUT does not automagically make data available to STDIN. And that's good, too: imagine code that looks like this:

#!/usr/bin/perl

use strict;
use warnings;

print STDOUT "What is your name? : ";
chomp ( my $name = <STDIN> );
print STDOUT "Hello, $name!\n";

exit;
[download]

Now, without running the above code, tell me: what do you expect the second print statement to print?

• Hello, What is your name? : blyman!
• Hello, blyman!

Yuck! Imagine if printing to STDOUT automagically made that data available to STDIN: you'd have to do some Olympian coding gymnastics to remove your STDOUT from your STDIN before you could find out what $name was entered as!

fwiw, I was confused about *why* STDOUT and STDIN aren't tied together - makes sense at first glance! - until I came up with the above code example. Hope this helps.

Update: realized greenFox was probably joking... but by golly, I learned something.

blyman
setenv EXINIT 'set noai ts=2'

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