Perl5 リファレンス



die

【文法】

die リスト


【説明】



               Outside an `eval', prints the value of LIST to
               `STDERR' and exits with the current value of `$!'
               (errno).  If `$!' is `0', exits with the value of
               `($? >> 8)' (backtick `command` status).  If `($?
               >> 8)' is `0', exits with `255'.  Inside an
               `eval(),' the error message is stuffed into `$@'
               and the `eval' is terminated with the undefined
               value.  This makes `die' the way to raise an
               exception.

               Equivalent examples:

                   die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news';
                   chdir '/usr/spool/news' or die "Can't cd to spool: $!\n"

               If the value of EXPR does not end in a newline,
               the current script line number and input line
               number (if any) are also printed, and a newline is
               supplied.  Note that the "input line number" (also
               known as "chunk") is subject to whatever notion of
               "line" happens to be currently in effect, and is
               also available as the special variable `$.'.  See
               the section on "$/" in the perlvar manpage and the
               section on "$." in the perlvar manpage.

               Hint: sometimes appending `", stopped"' to your
               message will cause it to make better sense when
               the string `"at foo line 123"' is appended.
               Suppose you are running script "canasta".

                   die "/etc/games is no good";
                   die "/etc/games is no good, stopped";

               produce, respectively

                   /etc/games is no good at canasta line 123.
                   /etc/games is no good, stopped at canasta line 123.

               See also exit(), warn(), and the Carp module.

               If LIST is empty and `$@' already contains a value
               (typically from a previous eval) that value is
               reused after appending `"\t...propagated"'.  This
               is useful for propagating exceptions:

                   eval { ... };
                   die unless $@ =~ /Expected exception/;

               If `$@' is empty then the string `"Died"' is used.

               die() can also be called with a reference
               argument.  If this happens to be trapped within an
               eval(), $@ contains the reference.  This behavior
               permits a more elaborate exception handling
               implementation using objects that maintain
               arbitary state about the nature of the exception.
               Such a scheme is sometimes preferable to matching
               particular string values of $@ using regular
               expressions.  Here's an example:

                   eval { ... ; die Some::Module::Exception->new( FOO => "bar" ) };
                   if ($@) {
                       if (ref($@) && UNIVERSAL::isa($@,"Some::Module::Exception")) {
                           # handle Some::Module::Exception
                       }
                       else {
                           # handle all other possible exceptions
                       }
                   }

               Because perl will stringify uncaught exception
               messages before displaying them, you may want to
               overload stringification operations on such custom
               exception objects.  See the overload manpage for
               details about that.

               You can arrange for a callback to be run just
               before the `die' does its deed, by setting the
               `$SIG{__DIE__}' hook.  The associated handler will
               be called with the error text and can change the
               error message, if it sees fit, by calling `die'
               again.  See the section on "$SIG{expr}" in the
               perlvar manpage for details on setting `%SIG'
               entries, and the section on "eval BLOCK" for some
               examples.  Although this feature was meant to be
               run only right before your program was to exit,
               this is not currently the case--the
               `$SIG{__DIE__}' hook is currently called even
               inside eval()ed blocks/strings!  If one wants the
               hook to do nothing in such situations, put

                       die @_ if $^S;

               as the first line of the handler (see the section
               on "$^S" in the perlvar manpage).  Because this
               promotes strange action at a distance, this
               counterintuitive behavior may be fixed in a future
               release.


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