source: npl/mediabox/lcdproc_edwin/src/clients/examples/tail.pl

#!/usr/local/bin/perl -w

use IO::Socket;
use Fcntl;

if($#ARGV < 0)
{
    print "Usage: tail.pl file\n";
    exit;
}
$filename = shift @ARGV;


# Connect to the server...
$remote = IO::Socket::INET->new(
                Proto     => "tcp",
                PeerAddr  => "localhost",
                PeerPort  => "13666",
        )
        || die "Cannot connect to LCDproc port\n";

# Make sure our messages get there right away
$remote->autoflush(1);

sleep 1;        # Give server plenty of time to notice us...

print $remote "hello\n";
my $lcdconnect = <$remote>;
print $lcdconnect;


# Turn off blocking mode...
fcntl($remote, F_SETFL, O_NONBLOCK);


# Set up some screen widgets...
print $remote "client_set name {Tail ($filename)}\n";
print $remote "screen_add tail\n";
print $remote "screen_set tail name {Tail $filename}\n";
print $remote "widget_add tail title title\n";
print $remote "widget_set tail title {Tail: $filename}\n";
print $remote "widget_add tail 1 string\n";
print $remote "widget_add tail 2 string\n";
print $remote "widget_add tail 3 string\n";


# These define the visible part of the file...
$top = 3;    # How far from the end of the file should we start?
$lines = 3;  # How many lines to display?
$left = 1;   # Left/right scrolling position,
$width = 20; # and number of characters per line to show

$slow = 1;   # Should we pause after the current frame?

# Forever, we should do stuff...
while(1)
{
        # Handle input...  (spew it to the console)
        # Also, certain keys scroll the display
        while(defined($input = <$remote>)) {
            print $input;

            $slow = -10;
            # Make sure we handle each line...
            @lines = split(/\n/, $input);
            foreach $line (@lines)
            {
                if($line =~ /^key (\S)/)  # Keypresses are useful.
                {
                    $key = $1;
                    if($key eq "G") { $top++; }
                    if($key eq "H") 
                    { 
                        if($top > $lines) {$top--; }
                    }
                    if($key eq "F") { $left++; }
                    if($key eq "E") 
                    { 
                        if($left > 1) {$left--; }
                    }
                }
            }
        }

        # Now, show what the file contains, if anything...
        if( -f $filename )
        {
            # Grab some text.
            $right = $left + $width - 1;
            $text = `tail -$top $filename | head -$lines | cut -c$left-$right`;
            @lines = split(/\n/, $text);
            # Now, display that text...
            for($i=0; $i<$lines; $i++)
            {
                $j = $i + 1;
                $k = $i + 2;
                if($#lines < $i) { $line = " "; }  # Avoid blank lines
                else { $line = $lines[$i]; }
                if(!($line =~ /\S/)) { $line = " ";}
                print $remote "widget_set tail $j 1 $k {$line }\n";
            }
        }
        else  # If the file is unreadable, show an error
        {
            print $remote "widget_set tail one 1 2 {$filename}\n";
            print $remote "widget_set tail two 1 3 {doesn't exist.}\n";
            print $remote "widget_set tail three 1 4 { }\n";
        }

        # And wait a little while before we show stuff again.
        if($slow > 0) {sleep 1; $slow++;}
        elsif($slow > 4) {sleep 2; $slow++;}
        elsif($slow > 64) {sleep 4; }
        else {$slow++;}
        # The "slow" thing just lets us have a better response time
        # while the user is pressing keys...  But while the user
        # is inactive, it gradually decreases update frequency.
}

close ($remote)            || die "close: $!";
exit;