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From: stuart@amc.com (Stuart Poulin)
Newsgroups: comp.lang.perl
Subject: Reading from /dev/tty in forked process.
Message-ID: <1991May24.163027.12281@amc.com>
Date: 24 May 91 16:30:27 GMT
Reply-To: stuart@anabol.amc.com ()
Distribution: na
Organization: Applied Microsystems, Redmond, WA
Lines: 81

Warning: I'm new to perl.

My question is how do you get perl to stop and read from /dev/tty when
you have a forked process sub function that is taking its' input from
STDIN.

For example, say under sh I decide write a "Pager" function that prints
a screen full of lines then prompts the user to hit return to get to
the next screen of lines. (I'm not interested in a "Pager", I'm just
using it here as an example.)  I might write is as such:

#!/bin/sh

Pager () {
PageSize=24
LineCount=1
while read i
do
    if [ $LineCount -gt $PageSize ] 
    if [ $LineCount -gt $PageSize ] 
		LineCount=1
		echo -n "Hit return to continue: " 
		( exec < /dev/tty
		  read X
		)
	fi
	echo $i
	LineCount=`expr $LineCount + 1 `
done
}

cat data | Pager

#--------------------------------------------
I can then use "Pager" anywhere in the rest of the script to pump
output through so it doesn't roll off the screen.

Thinking along these lines I tried this perl program:

#!/usr/local/bin/perl 

sub pager {
	local($pagesize,$linecount) = (24,1);
	open(TTYIN,"</dev/tty") || die "can't open /dev/tty: $!";
	while (<>) {
		if ( $linecount >= $pagesize ) {
			print  "Hit return to continue: ";
			$ans = <TTYIN>;
			print "\n" ;
			$linecount = 1;
		}
		print ; 
		$linecount++ ;
	}
	close(TTYIN);
}


$pid = open (OUT,"|-");
if (!$pid) {
	&pager;
	exit;
} else {
	open(INPUT,"data") || die "Cannot open data ";
	while(<INPUT>) {
		print OUT $_;
	}
}

This prints out the "Hit return to continue" messages but it doesn't
wait for the return, it keeps on going.

Most likely my problem is I'm not thinking in perl yet, but I'm
tryin'.

Thanks,
	Stuart

Stuart Poulin                           DNS: stuart@amc.com
Applied Microsystems Corporation        UUCP: amc-gw!stuart
Redmond, Washington  98073              Dial: 800-ASK-4AMC,206-882-2000