G'day h123,

Could you not simply use alarm? Here's a barebones example:

Perl script:

#!/usr/bin/env perl

use strict;
use warnings;
use autodie qw{:all};

my $command = './pm_test_no_echo_nl.sh';
my $timeout = 3;

my $pid = open my $pipe_from, '-|', $command;
local $SIG{ALRM} = sub { kill HUP => $pid; die "No data\n" };
alarm $timeout;

while (<$pipe_from>) {
    alarm 0;
    print;
    alarm $timeout;
}
[download]

Shell script:

#!/bin/sh

echo With newline
echo With newline
echo "NO newline\c"
sleep 5
echo With newline
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Output from running the shell script from the command line:

With newline
With newline
NO newlineWith newline
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[When the last line is output, "NO newline" appears immediately, then there's a 5 second delay, then "With newline" appears and the script ends.]

Output from the Perl script:

With newline
With newline
No data
[download]

[The first two lines (containing "With newline") appear immediately, then there's a 3 second delay, then "No data" appears and the script ends immediately.]

You should probably also read the documentation for "/home/<app>/client/bin/<stats>" to determine what the appropriate signal is (for kill) to terminate this program in case it's hanging rather than dying (kill 0 => $pid should tell you that): HUP was fine for my shell script; you may need something different.

See also open (for differences between my syntax and yours) and autodie.

Hi Ken, This is the thing I am looking for. Thanks you so much.

Is there a way to print "No data" every x seconds until program 'B' comes back up? I don't want to kill the process. I'd rather log No data every 10 seconds. If this makes sense?

You control the timeout activity with the coderef you assign to $SIG{ALRM}. There's no requirement to kill or die.

In the test shell script, I increased the delay (to get a few periods of no output) and added a loop (to emulate the stop/start behaviour):

#!/bin/sh

for i in {1..3}; do
    echo With newline
    echo With newline
    echo "NO newline\c"
    sleep 10
    echo With newline
done
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In the Perl script, I just changed

local $SIG{ALRM} = sub { kill HUP => $pid; die "No data\n" };
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to

local $SIG{ALRM} = sub { alarm 0; print "No data\n"; alarm $timeout };
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Here's the new output:

With newline
With newline
No data
No data
No data
NO newlineWith newline
With newline
With newline
No data
No data
No data
NO newlineWith newline
With newline
With newline
No data
No data
No data
NO newlineWith newline
[download]

Perhaps take a look at perlipc: Signals. This has more information on Signals in general; it also has another $SIG{ALRM} example.

-- Ken

Hi, At the moment I'm just printing to the screen to test but in my loop I have done something like this:

$STAT_LINE = "$_";
push (@TOTAL_STATS, $STAT_LINE);
if (@TOTAL_STATS >= $SPF) {
        foreach(@TOTAL_STATS) {print "$_"};
        splice @TOTAL_STATS;
        }
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But when there is no new line to print, the program just keeps waiting for a new line. What I want is a way to say that if there is no new line after 10 seconds push "Error" to the array

I don't see where this changes, assuming you have the time thing sorted out. If you don't, you could try something like

my $start_time = time();
my @data;
while (time() < $start_time + 10) {
# try to populate @data here
}

if (!@data) { print "error!\n"; } else { print @data; }
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Unless I'm misunderstanding the problem, which is entirely possible.