Does a fork(2) system call to create a new process running the same program at the same point. It returns the child pid to the parent process,
0 to the child process, or
undef if the fork is unsuccessful. File descriptors (and sometimes locks on those descriptors) are shared, while everything else is copied. On most systems supporting fork(), great care has gone into making it extremely efficient (for example, using copy-on-write technology on data pages), making it the dominant paradigm for multitasking over the last few decades.
Note: unflushed buffers remain unflushed in both processes, which means you may need to set
$| ($AUTOFLUSH in English) or call the
autoflush() method of
IO::Handle to avoid duplicate output.
fork() without ever waiting on your children, you will accumulate zombies. On some systems, you can avoid this by setting
"IGNORE". See also perlipc for more examples of forking and reaping moribund children.
Note that if your forked child inherits system file descriptors like STDIN and STDOUT that are actually connected by a pipe or socket, even if you exit, then the remote server (such as, say, a CGI script or a backgrounded job launced from a remote shell) won't think you're done. You should reopen those to /dev/null if it's any issue.