Thanks a million! You're totally right, it's just me miss using $!. I had just about figured all that out messing with it today, but I didn't understand the $! variable well enough. Thanks for explaining it to me.
James On Monday, October 14, 2002, at 02:33 PM, Michael Fowler wrote: > On Sun, Oct 13, 2002 at 09:50:58PM -0500, James Edward Gray II wrote: >> What's the best way to to track down the line that is setting the $! >> variable? I can't quite figure out the rules of this guy. Once it's >> set, >> what clears it? Its it localized to subroutines or packages or >> anything? >> I mean, if I'm printing this error out in once place, could it be >> happening in a far off chunk of code? > > $! is errno, which is set by various C functions to indicate what error > occurred. It is not, in itself, to be used as an indicator that there > is an > error, as it can be left in a non-zero state from any call. > > I suspect you're checking $! to see if an error occurred. What you > should > be doing is checking each operation (select, read, open, etc.) to see > if > there's an error, then checking $! to see what the reason is. That's > how $! > is supposed to be used. See the perldoc perlvar entry on $! for more > information. > > The way select() works could very well be setting $! to EBADF (the > error > you're seeing) as a normal part of its operation. The way select > works at > the C level is you pass it an integer indicated the largest > descriptor, then > three bit values indicating descriptors to check, then a timeout. What > select then does, based on various straces I've seen, is start at 0 > and go > up to the integer you gave it, testing each descriptor to see if it's > ready; > if the descriptor isn't actually one that's open, errno will be set to > EBADF, but select will simply ignore it. > > >> (I don't believe it's the select() complaining, but I'm not totally >> sure.) > > There's no way for select to return any sort of error. Just check > $nfound > to see if any descriptors are ready, and handle it from there. > > >> I've tried to use 'b CONDITION' in the debugger to track it down, but >> I >> can't figure out how to write the CONDITION. It always thinks I mean >> a >> subroutine. Any help here? Basically, any and all tips on the $! >> variable are needed. > > As I mentioned, $! is errno, which is set in a variety of functions, > most of > them from the C library. As a result, the Perl debugger is > insufficient for > tracking down problems with where it's set. The best way to find out > is to > use strace, ltrace, truss, or whatever system call or library call > tracer is > available on your system. > > However, most of the time you don't need to care where errno is set, > because > you're checking the operation that had the problem, and errno is just a > diagnostic telling you what problem occurred. > > > Michael > -- > Administrator www.shoebox.net > Programmer, System Administrator www.gallanttech.com > -- > > -- > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
