External command execution - Strange Error

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

I am executing a external command ( tar ) using backtick, while checking the return value it gives -1, and the $! gives no child process error. But the tar got created properly.

I tried the same with the system function also, but i get the same error.

Actually am new into the project, did not yet fully know/gonethrough/understood the framework - but referred other external command calls in the same project - and it is done the same way...

Machine is not having any problem: The machine/system which am using/testing this is not having any issue. Confirmed this by writing a sample program which creates a tar, $? gives 0 properly. So can somebody help me, what i have to look at ? Why do i get this error ?

I understand it is not possible to give solution by somebody else very easily. Actually am not looking for a solution, i spent a lot of time in fixing this... So i will be very happy to get atleast clues / guidance in finding out the issue. Thanks in advance.

Comment on External command execution - Strange Error - No child process

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Re: External command execution - Strange Error - No child process by toolic (Bishop) on Jul 25, 2011 at 16:12 UTC
I am executing a external command ( tar ) using backtick, while checking the return value it gives -1 Please show your code. What value do you expect backticks to return? Backticks return the output of the external command, which is different from the exit status of the command. See also system. and the $! gives no child process error Why are you checking $!? Maybe $? is more appropriate.	[reply]
Re: External command execution - Strange Error - No child process by zentara (Cardinal) on Jul 25, 2011 at 16:15 UTC
You should show some of the external command strings that you are using. Tar can be very difficult to get the option pairings right. In lieu of you showing no code, here is a option string that took me awhile to get correct. You may have an option wrong, or maybe you want to add 2>&1>/dev/null to your options to quiet the output. Passing the commandline options to tar, for example only, not tested recently: `system ('tar','-c','-XEXCLUDE_FILE','-M','-L50000',"-F ./backup-rotate +.pl $basename","-f$basename-0.tar",$dir);` [download] I'm not really a human, but I play one on earth. Old Perl Programmer Haiku ................... flash japh	[reply] [d/l]
Re: External command execution - Strange Error - No child process by ikegami (Patriarch) on Jul 25, 2011 at 18:35 UTC
Are you perhaps using $SIG{CHLD} to reap the child? (Oops, just saw this was already mentioned. Kudos to zentara.)	[reply]
Re: External command execution - Strange Error - No child process by Anonymous Monk on Jul 25, 2011 at 16:25 UTC
Sorry for not explaining it properly. When I meant, i checked the return/exit status. I checked the $? and found it as -1. If it is -1, we are supposed to check the $! which has the string - explanation of the error. The tar command I used is very simple, `tar -cf logs.tar logout.txt logerr.txt` Thanks for your reply.. Kindly help me in figuring out the issue.	[reply] [d/l]
Re^2: External command execution - Strange Error - No child process by zentara (Cardinal) on Jul 25, 2011 at 17:02 UTC
See no child process error in perl You are getting the return value from waitpid probably done automatically by the backticks. The solution is to set `$SIG{CHLD} = 'DEFAULT';` [download] in your Perl script. Or figure out how to localize it `local $SIG{CHILD} = 'IGNORE';` [download] I'm not really a human, but I play one on earth. Old Perl Programmer Haiku ................... flash japh	[reply] [d/l] [select]
Re^2: External command execution - Strange Error - No child process by cdarke (Prior) on Jul 26, 2011 at 08:43 UTC
Presumably you shifted $? to get the exit code: `$? >> 8` as documented in perlvar?	[reply] [d/l]
Re: External command execution - Strange Error - No child process by onelesd (Pilgrim) on Jul 26, 2011 at 06:39 UTC
The backtick operator returns the output of the command. The `system` function actually returns the exit value itself. If you want the exit value do this: `my $exit_value = system($tar_command) ; die "tar failed: ".$exit_value / 256."\n" if $exit_value != 0 ;` [download]	[reply] [d/l] [select]