Re: Jammed FH pipe

Start by not using a global var (*SNMP). If you insist, at least localize it. If it ceases to exist, it's hard for it to be "jammed".

Fixed along with *many* other problems:

sub {
    my ($target, $table, $fieldstring, $comstr) = @_;

    my @cmd = ( mibtable => (
        -table  => $table,
        -fields => $fieldstring,
        -node   => $target,
    );

    open(my $fr_child, '-|', @cmd)
        or die("Can't launch $cmd[0]: $!\n");

    while (<$fr_child>) {
        # do stuff
    }

    close($fr_child)
        or die("Can't wait for child: $!\n");

    die("Child died from signal ", ($? & 0x7F), "\n") if $? & 0x7F;
    die("Child died with code ",   ($? >> 8),   "\n") if $? >> 8;

    print("Child exited successfully\n");
}
[download]

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Re^2: Jammed FH pipe by gryf (Novice) on Oct 07, 2009 at 22:21 UTC
Thanks, I tried some of these changes to the 'open' line, but problems still choke the process: `$pid = open( my $fr_child, '-\|', @cmd) or die("Can't launch $cmd[0]: $!\n");` [download] fails with an error: `Can't use an undefined value as filehandle reference at testSnmp2.pl line 192.` Tweaked to look like this `$pid = open( my $fr_child, '-\|', $snmpCmd) or die("Can't launch $cmd[0]: $!\n");` [download] The open succeeds, but I get this error from the child proc `Child exited successfully !!!! Illegal seek / 0 /` [download] and I get no data back. Tweaked again to be `$pid = open( my $fr_child, $snmpCmd) or die("Can't launch $cmd[0]: $!\n");` [download] I get the following response: `Can't wait for child:` with an $? value of 256. If it helps, I'm running on Solaris 8.	[reply] [d/l] [select]
Re^3: Jammed FH pipe by ikegami (Patriarch) on Oct 07, 2009 at 22:57 UTC
I just noticed the 5.6 limit now. That explains some of the reasons my code won't do for you. Reverting to using `$snmpCmd` is wrong though. Sure, you'll need to provide the command as a string in 5.6, but you don't properly convert the args into shell literals at the moment. Nothing in my code can output "`!!!! Illegal seek / 0 /`", so I don't know anything about that. I get the following response: Can't wait for child: with an $? value of 256. Looks like there's a bug in Perl's design. There's no reliable way to tell if `close` returns a system error (`$!`) or a child error (`$?`). ( On second thought, we'll get the wrong error message at worse, so I will use `$!==0` ) sub to_shell_literal { my ($s) = @_; #return $s if m{^[a-zA-Z0-9/_-]+\z}; $s =~ s/'/'\\''/g; return "'$s'"; } sub { my ($target, $table, $fieldstring, $comstr) = @_; my @cmd = ( mibtable => ( -table => $table, -fields => $fieldstring, -node => $target, ); my $cmd = join ' ', map to_shell_literal($_), @cmd; open(my $fr_child, "$cmd \|") or die("Can't launch $cmd[0]: $!\n"); while (<$fr_child>) { # do stuff } if (!close($fr_child)) { die("Can't wait for child: $!\n") if $! != 0; die("Child died from signal ", $? & 0x7F, "\n") if $? & 0x7F; die("Child died with code ", $? >> 8, "\n") if $? >> 8; die("Unknown error waiting for child\n"); } print("Child exited successfully\n"); } [download] — Yeah, the documentation says `$!` will be zero in this instance, but I don't trust it. At least one other instance where the docs ignored "`$!` is only meaningful on error" has turned out to be wrong.	[reply] [d/l] [select]
Re^3: Jammed FH pipe by cdarke (Prior) on Oct 08, 2009 at 07:20 UTC
I don't know the mibtable program, but are you sure it works in a pipe? Is `Illegal seek` coming from perl or mibtable? I suggest you try the program with exactly the same parameters on the command-line piped to something like od(1). Maybe it is trying to do operations (like a seek) on the pipe which are illegal. An strace or truss might help as well.	[reply] [d/l]