CODEWITHSUNDEEP
perlwindows-services
user285686
user285686

Reputation: 195

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

Case 1

If I run below command i.e iperf in UL only, then I am able to capture the output 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.

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. I tried with readpipe() and exec() calls but these were also in vain.

Could someone 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 output to a txt file?

mobrule-- Finally I am able to achieve what I wanted. Below is the code I used, but now it is also giving me an error on each subsequent run...

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 change the file for taking output every time, then I am able to run it successfully one after another.

Could you please suggest how I can kill that process (rather than doing it manually from task manager) and get rid of that problem?

I tried to unlink the file used but that did not solve the problem.

Upvotes: 0

Views: 1830

Answers (1)

mob
mob

Reputation: 118695

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.

Upvotes: 1

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