Another Tied Hash: %!

• Perl magic $! variable reflects the operating system error status

• Example of use:

        unless (open FH, $filename) {
          if ($! == EACCES) {
            # Permission denied...
          } elsif ($! == ENOENT) {
            # No such file...
          } elsif ($! == ENOTDIR) {
            # Some part of the path is not a directory...
          } elsif ...
          }
        }

• This doesn't work---where did EACCESS etc. come from?

• Solution 1: Import lots and lots of compile-time constants. (Blecch.)

• Solution 2: Use %! instead: (5.005 and later.)

        unless (open FH, $filename) {
          if ($!{EACCES}) {
            # Permission denied...
          } elsif ($!{ENOENT}) {
            # No such file...
          } elsif ($!{ENOTDIR}) {
            # Some part of the path is not a directory...
          } elsif ...
          }
        }

• When Perl saw you use %!, it loaded the Errno module and tied %! into it.

• FETCH method checks the value of $!.

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Copyright © 2003 M. J. Dominus