Apologies. Here's a version that eliminates much of the extra stuff, and adds a bunch of comments:
#!/usr/bin/env perl
use strict;
use warnings;
use Time::HiRes qw(usleep);
use IO::Select;
use File::Spec::Functions qw(catfile);
use constant USLEEP_TIME => 25_000; # Microseconds
use constant RUN_TIME => 30; # Seconds
my $cmd = catfile((getpwnam($ENV{USER}))[7],'scripts','outputter'); #
+This just sets up the path to the external script.
print "Our command is >>>$cmd<<<\n";
open my $r, '-|', $cmd or die $!; # Open a pipe to read output f
+rom a command.
my $s = IO::Select->new($r); # Create an IO::Select object
+on our pipe's filehandle, $r.
my $pinged = 0; # Poor-man's messaging: We hav
+en't received a ping yet.
my $start = time(); # Record our start time so we
+can calculate when to exit.
while(time() < $start + RUN_TIME) { # Iterate until we run out of
+time.
if ($r->eof) { # Finish if the target command
+ has finished all output and termianted.
last;
}
elsif ($s->can_read(0)) { # See if there's something
+ available to read.
chomp(my $i = <$r>); # Read from our pipe and c
+homp.
print "\n<$i>\n"; # Print what we read.
$pinged = 1 if $i eq 'ping'; # Send a message that we r
+ead something.
}
elsif ($pinged) { # If we have a ping messag
+e, print a pong.
print "(pong)\n";
$pinged = 0; # And unset the message.
}
else {
usleep USLEEP_TIME; # If there's nothing to do
+, sleep briefly.
print '.'; # Print something to let e
+veryone know we're thinking of them.
STDOUT->flush;
}
} # lather, rinse, repeat.
Again, the "outputter" script (terribly named) should be:
#!/usr/bin/env perl
use strict;
use warnings;
use IO::Handle;
STDOUT->autoflush(1);
while (1) {
print STDOUT "ping\n";
sleep 2;
}
The output is going to look approximately like this:
Our command is >>>/home/......./scripts/outputter<<<
......................................................................
+..........
<ping>
(pong)
......................................................................
+..........
<ping>
(pong)
.................................^C
Command terminated
If I had let it run long enough it would time out and exit cleanly.
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