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$CHILD_ERROR
$?

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.