die - raise an exception or bail out
die LIST
Outside of 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. 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() and warn().
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.
You can arrange for a callback to be called 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.
Note that the $SIG{__DIE__} hook is 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).