Perl non-blocking user input - perl

Question

#!/usr/bin/perl -w
use Term::ReadKey;
ReadMode('cbreak');
while (1) {
$char = ReadKey(-1);
next unless defined $char;
printf("Char: $char Decimal: %d\tHex: %x\n", ord($char), ord($char));
}
ReadMode('normal');
The above works great. But i want to be able to get user input while some executable is running. so i ve tried the below but its not working. maybe running an executable while trying to get a user input is messing up? if so, how do i go about doing it?
I am getting output from $myexe and depending on the user input, i would like to filter differnt things from $myexe
#!/usr/bin/perl -w
use Term::ReadKey;
my $myexe = 'bin/myexecutable';
open my $EXE,
"$myexe distribute 2>&1 |"
or die 'Cannot open EXE';
ReadMode('cbreak');
while (<$EXE>) {
$char = ReadKey(-1);
if (defined $char) {
print ">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> $char\n"; #i would press a key but nothin prints out
}
print "$_\n";
}
ReadMode('normal');

Answer 1

I'm wary of running a 'busy-wait' loop like you'd get with Term::ReadKey. But what I'd suggest - if you're trying to do two things at once - is that it may be worth considering doing a spot of parallel code.
Something like:
#!/usr/bin/perl
use strict;
use warnings;
use threads;
use threads::shared;
use Term::ReadKey;
my $myexe = 'bin/myexecutable';
my $filter : shared;
sub worker {
open my $EXE, "$myexe distribute 2>&1 |"
or die 'Cannot open EXE';
while ( my $line = <$EXE> ) {
#do something with filter here;
print "$filter : $line";
}
}
$filter = 0;
threads->create( \&worker );
my $keypress;
ReadMode 4;
while ( threads->list(threads::running) ) {
while ( not defined( $keypress = ReadKey(-1) )
and threads->list(threads::running) )
{
print "Waiting\nRunning:" . threads->list(threads::running) . "\n";
sleep 1;
}
print "Got $keypress\n";
$filter = $keypress;
}
ReadMode 0;
foreach my $thr ( threads->list ) {
$thr->join();
}
This is some fairly simple example code - you can extend it in a variety of ways, but the principle is this:
you start a thread to 'do the work'.
you handle the 'keypress watching' in the 'main' thread.
Because there's a sleep in there, you're not busy-waiting on a keypress (e.g. polling as fast as a processor will spin).