Mark_Galeck has asked for the wisdom of the Perl Monks concerning the following question:

Hello, (I am not sure if this is a Perl question, or is more a general programming question. If the latter, then I am sorry to post here, please say so and I will begone. )

Every child in kindergarten knows what this does:

while (<>) {
  process $_
}

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What I want, is to get into the loop not only when a new line arrives, but also, after 1 second of waiting for it, (in which case $_ should be empty). I am thinking along the lines of fork or something, but it's going to be somewhat ugly. Is there a nice "monk" way to do this? Thank you, Mark

Replies are listed 'Best First'.
Re: how to use angle operator with timeout?
by tobyink (Canon) on Feb 03, 2013 at 23:35 UTC

    Try Prompt::Timeout or IO::Prompter.

    The basic technique just involves the alarm function...

    use 5.010;
use strict;
use warnings;
use Try::Tiny;

my $line;

try {
    local $SIG{ALRM} = sub { die "ALARM\n" };
    alarm 10;
    say "Please enter some text, but quick!";
    $line = <>;
    chomp $line;
    alarm 0;
}
catch {
    my $e = shift;
    $e =~ /^ALARM/ ? warn("timeout\n") : die($e);
};

say "Got: '$line'";

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    package Cow { use Moo; has name => (is => 'lazy', default => sub { 'Mooington' }) } say Cow->new->name
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[d/l]
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      Does that work on *nix? Cos it never times out on Windows.

      With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
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[reply]

        "Does that work on *nix? Cos it never times out on Windows."

        Works for me (on Linux).

        package Cow { use Moo; has name => (is => 'lazy', default => sub { 'Mooington' }) } say Cow->new->name
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      Thank you Monks very much, I appreciate your help! Yes this does work for me. Thank you!
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Re: how to use angle operator with timeout?
by Mr. Muskrat (Canon) on Feb 04, 2013 at 18:55 UTC

    Every child in kindergarten knows what this does: 

    while (<>) {
  process $_
}

    [download]

    Don't I wish!

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[d/l]
Re: how to use angle operator with timeout?
by Khen1950fx (Canon) on Feb 05, 2013 at 07:23 UTC
    I couldn't get alarm to work for me in a consistent manner, so I tried Tie::Scalar::Timeout. 
    #!/usr/bin/perl -l

use strict;
use warnings;
use Tie::Scalar::Timeout;

tie my $line, 'Tie::Scalar::Timeout',
  EXPIRES => '+1s', POLICY => undef;

$line = system("whoami");

while (defined($_ = $line)) {
    foreach $line(my @lines) {
        print "$_" or die $@;
    }
}

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[d/l]

      couldn't get alarm ....

      What has that nonsense got to do with readline, ie the OPs question?

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