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"
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If the last element of LIST 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 $.. See perlvar/"$/"
and perlvar/"$.".
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";
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produce, respectively
/etc/games is no good at canasta line 123.
/etc/games is no good, stopped at canasta line 123.
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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/;
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If LIST is empty and $@ contains an object reference that has a PROPAGATE
method, that method will be called with additional file and line number parameters. The
return value replaces the value in $@. ie. as if <$@ = eval { $@-PROPAGATE(__FILE__,
__LINE__) };>> were called.
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 arbitrary 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
}
}
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Because perl will stringify uncaught exception messages before displaying them, you may
want to overload stringification operations on such custom exception objects. See overload for details about
that.
You can arrange for a callback to be run just before the die does its
deed, by setting the $SIG{__DIE__} hook. The associated handler will be
called with the error text and can change the error message, if it sees fit, by calling die
again. See perlvar/$SIG{expr}
for details on setting %SIG entries, and "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 $SIG{__DIE__} hook is
currently called even inside eval()ed blocks/strings! If one wants the hook to do nothing
in such situations, put
as the first line of the handler (see perlvar/$^S). Because
this promotes strange action at a distance, this counterintuitive behavior may be fixed in
a future release.
