How can I get the output of a command terminated by a alarm() call in Perl?

Question

Case 1

If I run below command i.e iperf in UL only, then i am able to capture the o/p in txt file

@output = readpipe("iperf.exe -u -c 127.0.0.1 -p 5001 -b 3600k -t 10 -i 1");
open FILE, ">Misplay_DL.txt" or die $!;
print FILE @output;
close FILE;

Case 2

When I run iperf in DL mode , as we know server will start listening in cont. mode like below even after getting data from client (Here i am using server and client on LAN)

@output = system("iperf.exe -u -s -p 5001 -i 1");

on server side:

D:\_IOT_SESSION_RELATED\SEEM_ELEMESNTS_AT_COMM_PORT_CONF\Tput_Related_Tools\AUTO
MATION_APP_\AUTOMATION_UTILITY>iperf.exe -u -s -p 5001
------------------------------------------------------------
Server listening on UDP port 5001
Receiving 1470 byte datagrams
UDP buffer size: 8.00 KByte (default)
------------------------------------------------------------
[1896] local 192.168.5.101 port 5001 connected with 192.168.5.101 port 4878
[ ID] Interval Transfer Bandwidth Jitter Lost/Total Datagrams
[1896] 0.0- 2.0 sec 881 KBytes 3.58 Mbits/sec 0.000 ms 0/ 614 (0%)

command prompt does not appear , process is contd...

on client side:

D:\_IOT_SESSION_RELATED\SEEM_ELEMESNTS_AT_COMM_PORT_CONF\Tput_Related_Tools\AUTO
MATION_APP_\AUTOMATION_UTILITY>iperf.exe -u -c 192.168.5.101 -p 5001 -b 3600k -t
2 -i 1
------------------------------------------------------------
Client connecting to 192.168.5.101, UDP port 5001
Sending 1470 byte datagrams
UDP buffer size: 8.00 KByte (default)
------------------------------------------------------------
[1880] local 192.168.5.101 port 4878 connected with 192.168.5.101 port 5001
[ ID] Interval Transfer Bandwidth
[1880] 0.0- 1.0 sec 441 KBytes 3.61 Mbits/sec
[1880] 1.0- 2.0 sec 439 KBytes 3.60 Mbits/sec
[1880] 0.0- 2.0 sec 881 KBytes 3.58 Mbits/sec
[1880] Server Report:
[1880] 0.0- 2.0 sec 881 KBytes 3.58 Mbits/sec 0.000 ms 0/ 614 (0%)
[1880] Sent 614 datagrams

D:\_IOT_SESSION_RELATED\SEEM_ELEMESNTS_AT_COMM_PORT_CONF\Tput_Related_Tools\AUTO
MATION_APP_\AUTOMATION_UTILITY>

so with this as server is cont. listening and never terminates so can't take output of server side to a txt file as it is going to the next command itself to create a txt file

so i adopted the alarm() function to terminate the server side (iperf.exe -u -s -p 5001) commands after it received all data from the client.

could anybody suggest me the way..

Here is my code:

#! /usr/bin/perl -w
my $command = "iperf.exe -u -s -p 5001";
my @output;
eval {
    local $SIG{ALRM} = sub { die "Timeout\n" };
    alarm 20;
    #@output = `$command`;
#my @output = readpipe("iperf.exe -u -s -p 5001");
#my @output = exec("iperf.exe -u -s -p 5001");

my @output = system("iperf.exe -u -s -p 5001");
    alarm 0;
};
if ($@) {
    warn "$command timed out.\n";
} else {
    print "$command successful. Output was:\n", @output;
}
open FILE, ">display.txt" or die $!;
print FILE @output_1;
close FILE;

i know that with system command i cannot capture the o/p to a txt file but i tried with readpipe() and exec() calls also but in vain...

could some one please take a look and let me know why the iperf.exe -u -s -p 5001 is not terminating even after the alarm call and to take the out put to a txt file

Answer 1

Since the command might time out, you'll want to save as much output as you can while the command is running. Two ways to do this are:

1. Save the output to a file and read the file contents after the command finishes or times out:

   my @command_output;
   eval { 
       $SIG{ALRM} = { die "timeout\n" };
       alarm(30);
       system("$command > $file");
       alarm(0);
   };
   open my $fh, '<', $file;  # error handling omitted for brevity
   @command_output = <$fh>;
   close $fh;     # oops, this said "close $file" before ... not a big deal.
   

2. Run the command with open in -| mode and save as much output as you can while the command is running:

   my @command_output = ();
   eval {
       $SIG{ALRM} = { ... };
       alarm(30);
       open my $process, "$command |"; # or open my $process, '-|', $command
       while (<$process>) {
           push @command_output, $_;
       }
       close $process;
       alarm(0);
   };
   

---

In for a penny, in for a pound.

After figuring out what iperf.exe was and downloading it, I got this script to "work":

use strict;
use warnings;
my $command = "C:/cygwin/usr/local/bin/iperf.exe -u -s -p 25005";
my $file = "abc6.txt";
my ($pid,@command_output);
eval {
    my $process;
    $SIG{ALRM} = sub { 
      kill 'INT', $pid;
      close $process;
      die "timeout\n" 
    };
    alarm(10);
    $pid = open $process, "$command |";
    while (<$process>) {
      push @command_output, $_;
    }
    close $process;
    alarm(0);
};
print "eval block result was: $@\n";
print "Output was:\n------\n",@command_output;

I strongly urge you to familiarize yourself with all of the functions and syntax of this code before you try to get too much use out of it.

Answer 2

@mobrule
Finally i am able to achieve what i wanted, below is code used, but now it is giving me also an error on each subsequent Runs...

Error Message::

The process cannot access the file because it is being used by another process.iperf.exe -u -s -p 5001 successful. Output was:

code::

my @command_output; eval { my $file = "abc6.txt";
$command = "iperf.exe -u -s -p 5001"; alarm 10; system("$command > $file"); alarm 0; close $file; }; if ($@) { warn "$command timed out.\n"; } else { print "$command successful. Output was:\n", $file; } unlink $file;

Output::

abc6.txt

Server listening on UDP port 5001 Receiving 1470 byte datagrams

UDP buffer size: 8.00 KByte (default)

[1892] local 192.168.5.101 port 5001 connected with 192.168.5.101 port 3553 [ ID] Interval Transfer Bandwidth Jitter Lost/Total Datagrams [1892] 0.0- 2.0 sec 881 KBytes 3.61 Mbits/sec 0.000 ms 0/ 614 (0%)

also when for each run of this "iperf.exe" the process always remains live in Taskmanager, if i kill it manually before each Run OR changing the file for taking o/p every time, then i am able to run it successfully one after another

could you please suggest how can i kill that process rather than doing it manually from taskmanager and get rid of that problem

i tried to unlink the file used but that did not solve the purpose thank rocky..