In Perl, how do I process input as soon as it arrives, instead of waiting for newline?

Question

I'd like to run a subcommand from Perl (or pipe it into a Perl script) and have the script process the command's output immediately, rather than waiting for a timeout, a newline, or a certain number of blocks. For example, let's say I want to surround each chunk of input with square brackets. When I run the script like this:

$ ( echo -n foo ; sleep 5 ; echo -n bar ; sleep 5; echo baz) | my_script.pl

I'd like the output to be this, with each line appearing five seconds after the previous one:

[foo]
[bar]
[baz]

How do I do that?

This works, but is really ugly:

#! /usr/bin/perl -w

use strict;
use Fcntl;

my $flags = '';
fcntl(STDIN, F_GETFL, $flags);
$flags |= O_NONBLOCK;
fcntl(STDIN, F_SETFL, $flags);

my $rin = '';
vec($rin,fileno(STDIN),1) = 1;
my $rout;

while (1) {
  select($rout=$rin, undef, undef, undef);
  last if eof();

  my $buffer = '';

  while (my $c = getc()) {
    $buffer .= $c;
  }

  print "[$buffer]\n";
}

Is there a more elegant way to do it?

Answer 1

From perlfaq5: How can I read a single character from a file? From the keyboard?. You probably also want to read How can I tell whether there's a character waiting on a filehandle?. Poll the filehandle. If there is a character there, read it and reset a timer. If there is not character there, try again. If you've retried and passed a certain time, process the input.

After you read the characters, it's up to you to decide what to do with them. With all the flexibility of reading single characters comes the extra work of handling them.

Answer 2

Term::ReadKey can do this for you. In particular setting the ReadKey() mode to do the polling for you.

use Term::ReadKey;

$| = 1;
while( my $key = ReadKey(10) ) {
    print $key;
}