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 $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).