Path: utzoo!attcan!uunet!wuarchive!emory!hubcap!mephisto!mcnc!uvaarpa!mmdf
From: martin%easby.durham.ac.uk@CUNYVM.CUNY.EDU (Martin Ward)
Newsgroups: comp.lang.perl
Subject: (none)
Message-ID: <1990Jul17.095951.8569@uvaarpa.Virginia.EDU>
Date: 17 Jul 90 09:59:51 GMT
Sender: mmdf@uvaarpa.Virginia.EDU (Uvaarpa Mail System)
Reply-To: martin%easby.durham.ac.uk@CUNYVM.CUNY.EDU
Organization: The Internet
Lines: 32


John Watson writes:
| I have a perl script that needs to send a few lines to a filter
| process and read a few lines back.  (I have no sockets, forget that.)

This was exactly the problem I had with my "file viewer" program,
"t-rayc@microsoft.uucp" suggested the technique used below to pass the global
string $buf through a filter passed to &filterbuf. More generally you could
pass the buffer as another argument and return the filtered result.

sub filterbuf          # Pass $buf through the given filter.
  local ($filter) = @_;
  unless(open(GOODS, "-|"))    # produces the goods
    # child is here, with its stdout attached to parent's GOODS
    # child sends output of filter to stdout to be picked up by parent
    # Now the child redirects its STDIN to the output of a grandchild
    # which prints $buf to stdout (unbuffered):
    unless(open(STDIN,"-|"))  $| = 1; print $buf; exit 0; 
    # Now the child can run the filter - its stdin reads the $buf chars,
    # and its stdout is redirected to paren't GOODS filehandle:
    open(STDERR, ">/dev/null"); $| = 1; exec $filter;
    die "Couldn't exec. ($!)";
  
  read(GOODS, $buf, 1024);      # read up to 1024 filtered chars
  close(GOODS);         # wait for child to terminate.


		Martin.

My ARPANET address is:  martin%EASBY.DUR.AC.UK@CUNYVM.CUNY.EDU
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