The status returned by the last pipe close, backtick (``
) command, successful call to wait()
or waitpid()
, or from the system()
operator. This is just the 16-bit status word returned by the traditional Unix wait()
system call (or else is made up to look like it). Thus, the exit value of the subprocess is really ($? >> 8
), and $? & 127
gives which signal, if any, the process died from, and $? & 128
reports whether there was a core dump.
Additionally, if the h_errno
variable is supported in C, its value is returned via $?
if any gethost*()
function fails.
If you have installed a signal handler for SIGCHLD
, the value of $?
will usually be wrong outside that handler.
Inside an END
subroutine $?
contains the value that is going to be given to exit()
. You can modify $?
in an END
subroutine to change the exit status of your program. For example:
END {
$? = 1 if $? == 255; # die would make it 255
}
Under VMS, the pragma use vmsish 'status'
makes $?
reflect the actual VMS exit status, instead of the default emulation of POSIX status; see "$?" in perlvms for details.
Mnemonic: similar to sh and ksh.