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How can we make a system call within Perl

Posted on 2011-03-16
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Last Modified: 2012-05-11
Hi,
How can we make a system call within Perl?

For example, I do the following in the command line. Now I wanna make the same in Perl.

java -jar myFirstcode.java input1 input2

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Thanks,
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Question by:Tolgar
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9 Comments
 

Author Comment

by:Tolgar
ID: 35153239
Also, let's say for some reason it cannot make the system call. How can I catch the exception in try catch?

Can you please send me an example code that is very safe in handling this exception?

Thanks,
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LVL 16

Assisted Solution

by:sjklein42
sjklein42 earned 1000 total points
ID: 35153248
You can use the backtick operator:


$output  = `java -jar myFirstcode.java input1 input2`;

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There is also a system() function that does pretty much the same thing.
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LVL 16

Expert Comment

by:sjklein42
ID: 35153270
The exit status is available in $?

$output  = `java -jar myFirstcode.java input1 input2`;
$program_retval = $? >> 8;

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Author Comment

by:Tolgar
ID: 35153355
I did this. I think it is same as your first suggestion:

system("java -jar myFirstcode.java input1 input2");

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But I didn't understand your second reply. Is it related with the second part of my question which is about catching exceptions?

Thanks,
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LVL 16

Expert Comment

by:sjklein42
ID: 35153423
Hi.

Using system is fine, too.

Yes, my second note had to do with how to examine the $? variable to determine the status of the command.  It applies to the system function as well as to the backtick operator.
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LVL 26

Accepted Solution

by:
wilcoxon earned 1000 total points
ID: 35153440
They are two different but similar solutions.

system("java -jar myFirstcode.java input1 input2");

or

$output  = `java -jar myFirstcode.java input1 input2`;

will both make the system call.  After doing either, you should do something like the following to catch errors (taken from perldoc -f system):
if ($? == -1) {
    print "failed to execute: $!\n";
} elsif ($? & 127) {
    printf "child died with signal %d, %s coredump\n",
    ($? & 127),  ($? & 128) ? 'with' : 'without';
} else {
    printf "child exited with value %d\n", $? >> 8;
}

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LVL 26

Expert Comment

by:wilcoxon
ID: 35153442
The advantage to backticks is that you can capture the output of the call.  If you don't need to do that, I would use system.
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LVL 16

Expert Comment

by:sjklein42
ID: 35153460
@wilcoxon is the expert on this.  What he say.
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Author Closing Comment

by:Tolgar
ID: 35153507
Both solutions are very good but I picked wilcoxon's solution as best becasue it covers both questions and two different methods in a very descriptive way. But as I said both solutions are great.

Thanks,
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