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new to perl.. how do I do this ? fork/ threads ?

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# 1  
Old 05-01-2007
new to perl.. how do I do this ? fork/ threads ?
I have never coded in perl before (just started today morning Smilie. I need to write a perl program to automate a task.

Here is how I do it manually:

Start a program in my home dir. Now if I want to execute another program while this one is still running, what I would do is go to another terminal and then run it there in my home dir. While these 2 programs are running and I need to run another program then I will simply start another terminal and run the third one there.

But I want to automate this using perl. So I will have a perl script which will have 3 system calls:

$output1 = `./program1`;
$output2 = `./program2`;
$output3 = `./program3`;

# All 3 programs are finished. Do something with these output strings

But here, program2 will not be started until program1 has returned so it will have to unnecessarily wait. I want all 3 programs to run in parallel. And only once when all system calls have returned, go ahead and process the output strings.

So what do I need to do? use forks or threads ?

(note that Im using backticks `` to execute the system command, but I think there are other ways to do it such as system() etc.. I am free to use anything I want. Also, in the example I take the output in a string.. however I will eventually have the system calls direct the output to a file)

Thanks !!!
# 2  
Old 05-01-2007
Use fork() and then exec().
# 3  
Old 05-02-2007
Can I use fork() to start more than 1 child processes ?


What I have so far is:

Quote:
my $pid = fork();

if (not defined $pid) {

print "resources not avilable.\n ";

}
if ($pid == 0) {

#
# child process - Do something here !
#

} else {

#
# parent process - Do something here !
#

waitpid($pid,0);

#Both child and parent has finished.
}
But this will spawn off 1 child and I have 1 parent. But I need 3 processes. ANd all 3 should be doing something else.

Please help !!! Smilie
# 4  
Old 05-02-2007
Quote:
Originally Posted by the_learner
# parent process - Do something here !
"Do something here" can be to fork another process.
# 5  
Old 05-02-2007
Hey when I have the child process run a program, the parent process does not proceed until the child has finished...

Quote:
my $pid = fork();

if ($pid == 0) {

#
# child process
#

my $output1 = `./program1`;

# the above program takes 5 mins to complete.

} else {

#
# parent process
#

print 'Hello, I am parent';

waitpid($pid,0);

#Both child and parent has finished.
}
program1 takes 5 mins to complete. The parent does not print 'Hello, I am parent' until the child has finished.
# 6  
Old 05-02-2007
Quote:
Originally Posted by the_learner
The parent does not print 'Hello, I am parent' until the child has finished.
My guess is that output buffering is getting in the way. Try
Code:
print STDERR 'Hello, I am parent';

# 7  
Old 05-02-2007
For output buffering, either you add a "\n" at the end (as Perl IO is line buffered), or set

$| = 1;

at the top of the program.
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