Programming Perl, 4th Edition

die

die LIST
die

Outside an eval, this function prints the concatenated value of LIST to STDERR and exits with the current value of $! (the C library’s errno variable). If $! is 0, it exits with the value of ($? >> 8), the status of the last reaped child from a system, wait, close on a pipe, or `command`. If ($? >> 8) is 0, it exits with 255.

Within an eval, the function sets the $@ variable to the error message that would have otherwise been produced, then aborts the eval, which returns undef. The die function can thus be used to raise named exceptions that can be caught at a higher level in the program. See eval later in this chapter.

If LIST is a single object reference, that object is assumed to be an exception object and is returned unmodified as the exception in $@ (described below).

If LIST is empty and $@ already contains a string value (typically from a previous eval) that value is reused after appending “\t...propagated”. This is useful for propagating (reraising) exceptions:

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

If LIST is empty and $@ already contains an exception object, that object’s $@–>PROPAGATE method is invoked with additional file and line number parameters to determine how the exception should propagate, with its return value replacing the value in $@. That is, it’s as if $@ = eval { $@–>PROPAGATE(_ _FILE_ _, _ _LINE_ _) } were called.

If LIST is empty ...