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system function is returning status -1 when running a unix command

by elf_firein (Novice)
on Apr 08, 2009 at 05:07 UTC ( #756229=perlquestion: print w/ replies, xml ) Need Help??
elf_firein has asked for the wisdom of the Perl Monks concerning the following question:

I am facing a strange problem with perl code. I have a perl package abc.pm which has following subroutine:
sub DB_xxx { my ($dbUser, $dbPass, $db, $autoCommit) = @_; my $dbh; # logon to DB unless( $dbh = DBI->connect('dbi:Oracle:' . ($$db || ''), $$dbUser +, $$dbPass, {AutoCommit => $$autoCommit}) ) { croak "Error connecting to database $DBI::errstr \n"; } return $dbh; }

This method is for connecting to database

Inside my own .pl file I am using this subroutine in following manner:
use abc qw (DB_xxx); my $dbh; my $stat1 = system ("gzip -t xyz.gz"); print "The stat checking:$stat1\n"; my $userid = xxx; my $passwd = xxx; my $database = xyz; my $autocommit = 0; $dbh=DB_xxx(\$userid, \$passwd, \$database, \$autocommit); my $stat2 = system ("gzip -t xyz.gz"); print "The stat checking:$stat2\n";

The problem is:the value of $stat1 is 0 but value of $stat2 is -1. though the .gz file is same in same location. In Solaris 8 box but in $stat1 & $stat2 have values 0 for both. But in solaris 10 box giving to two differnt output:$stat1=0 & $stat2=-1

I have also printed $!: For $stat2 it is showing error message: / No child process/

Can anybody please help me? Please it is urgent.

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Re: system function is returning status -1 when running a unix command
by ikegami (Pope) on Apr 08, 2009 at 06:01 UTC
    Sounds like your DB stuff is messing with SIGCHLD.
    $ perl -wle'$SIG{CHLD}="IGNORE"; print system("ls -d ."); print $!' . -1 No child processes

    system is basically fork + exec (in the child) + waitpid (in the parent). In the above example, children are auto-reaped, so system has no child to wait for, so it returns an error.

    strace (or truss or whatever it's called on Solaris) would confirm this diagnosis.

    Update: Added last line.

      ikegami, could you please explain what is going on here:
      > perl -wle ' $SIG{CHLD}="IGNORE"; $! = 33; print system("ls -d ."); print -+-$!; print $!; print -+-$!' . -1 33 No child processes 10

      It seems that string-ifying "$!" changes its value.

        print can result in system calls. $! is meaningless after the first print.

        $ perl -wle' $SIG{CHLD}="IGNORE"; $! = 0; my $rv = system("ls -d ."); my $errno = $!; print $rv; print 0+$errno; print $errno; print 0+$errno; ' . -1 10 No child processes 10

        Note that 0+ is much easier to understand than -+-, and it conveys the intent much better.

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