diff options
| -rw-r--r-- | pod/perlvar.pod | 22 |
1 files changed, 19 insertions, 3 deletions
diff --git a/pod/perlvar.pod b/pod/perlvar.pod index 5d04e224a7..1e6350bd7f 100644 --- a/pod/perlvar.pod +++ b/pod/perlvar.pod @@ -673,9 +673,25 @@ see L<encode>. An opaque C<Encode::XS> object. =item $! If used numerically, yields the current value of the C C<errno> -variable, with all the usual caveats. (This means that you shouldn't -depend on the value of C<$!> to be anything in particular unless -you've gotten a specific error return indicating a system error.) +variable, or in other words, if a system or library call fails, it +sets this variable. This means that the value of C<$!> is meaningful +only I<immediately> after a B<failure>: + + if (open(FH, $filename)) { + # Here $! is meaningless. + ... + } else { + # ONLY here is $! meaningful. + ... + # Already here $! might be meaningless. + } + # Since here we might have either success or failure, + # here $! is meaningless. + +In the above I<meaningless> stands for anything: zero, non-zero, +C<undef>. A successful system or library call does B<not> set +the variable to zero. + If used an a string, yields the corresponding system error string. You can assign a number to C<$!> to set I<errno> if, for instance, you want C<"$!"> to return the string for error I<n>, or you want |