die function
Raise an exception or bail out
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. 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 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 $SIG{expr}
for details on setting %SIG entries, and 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 $^S).
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