Comment by sltkr

> when I asked on IRC the only answer I got was 'man perldoc'

Your overall point notwithstanding, this was just bad advice. What you want is `man perlvar` (or equivalently `perldoc perlvar`) which documents this and other predefined variables:

       HANDLE->autoflush( EXPR )
       $OUTPUT_AUTOFLUSH
       $|      If set to nonzero, forces a flush right away and after every
               write or print on the currently selected output channel.
               Default is 0 (regardless of whether the channel is really
               buffered by the system or not; $| tells you only whether you've
               asked Perl explicitly to flush after each write).  STDOUT will
               typically be line buffered if output is to the terminal and
               block buffered otherwise.  Setting this variable is useful
               primarily when you are outputting to a pipe or socket, such as
               when you are running a Perl program under rsh and want to see
               the output as it's happening.  This has no effect on input
               buffering.  See "getc" in perlfunc for that.  See "select" in
               perlfunc on how to select the output channel.  See also
               IO::Handle.

               Mnemonic: when you want your pipes to be piping hot

Also, `man perl` gives a great overview of the extensive number of Perl-related manpages. I think any person that starts from `man perl` will be able to answer a lot of their questions, but part of the problem was that around the millennium, people stopped reading man-pages, and started looking for information on the web. perl was one of those old-school tools that were documented extensively in man-pages, but past 1995 ~nobody bothered to read man-pages anymore.