# SPDX-License-Identifier: GPL-2.0
# Prefix all lines with "# ", unbuffered. Command being piped in may need
# to have unbuffering forced with "stdbuf -i0 -o0 -e0 $cmd".
use strict;
use IO::Handle;

binmode STDIN;
binmode STDOUT;

STDOUT->autoflush(1);

my $needed = 1;
while (1) {
    my $char;
    my $bytes = sysread(STDIN, $char, 1);
    exit 0 if ($bytes == 0);
    if ($needed) {
        print "# ";
        $needed = 0;
    }
    print $char;
    $needed = 1 if ($char eq "\n");
}