A. Creating a web counter for your home page.
1. Create a file on disk that will store the number of accesses.
This number will be updated everytime the page is requested.
Create
Here's that sequence of actions for me:/u/yourUsername/httpd/counters (the directory) /u/yourUsername/httpd/counters/homepage.counter (the actual counter) /u/yourUsername/httpd/counters/homepage.semaphore (semaphore, for access)
2. Create a script that updates the counter and displays the updated value.tucotuco.cs.indiana.edu% pwd /nfs/paca/home/user2/dgerman/httpd tucotuco.cs.indiana.edu% ls -l counters counters: No such file or directory tucotuco.cs.indiana.edu% mkdir counters tucotuco.cs.indiana.edu% cd counters tucotuco.cs.indiana.edu% vi homepage.counter tucotuco.cs.indiana.edu% cat homepage.counter 0 tucotuco.cs.indiana.edu% vi homepage.semaphore tucotuco.cs.indiana.edu% cat homepage.semaphore tucotuco.cs.indiana.edu% ls -l homepage* -rw-r--r-- 1 dgerman students 2 Oct 21 13:09 homepage.counter -rw-r--r-- 1 dgerman students 0 Oct 21 13:09 homepage.semaphore tucotuco.cs.indiana.edu%
Store this script in
Here's the code, with comments:httpd/cgi-bin/homepage
#!/usr/bin/perl
use GD; # enough said
print "Content-type: image/gif\n\n"; # MIME type of produced document
$location = "/u/yourUsername/httpd/counters"; # this is where we keep the counters, one per page
# there are two files per counter, one semaphore and one datafile
open (U, "$location/homepage.semaphore"); # open the semaphore
flock(U, 2); # 2 is for exclusive lock set on the file (resource)
open (M, "$location/homepage.counter"); # now open the datafile
$x = <M>; # read the number inside
close(M); # close the datafile
$x += 1; # increase the number by one
# at this point the semaphore is locked, if any other hits are
# occurring now the processes wait for us to release the lock
open (M, ">$location/homepage.counter"); # getting ready to update the datafile
print M $x, "\n"; # overwrite previous number with the new value
close(M); # close the datafile
flock(U, 8); # finally, release the lock on the semaphore so that someone
# else that wants to work with the counter can seize it
# from here on we're doing display
$counter = sprintf(" %s ", $x); # create a string ($counter) from $x
$counter_length = length($counter); # find out how long it is (how many chars)
$font_length = 8; # set the font size (length) in pixels
$font_height = 16; # set the font size (width) in pixels
$x = $font_length * $counter_length; # deduce the length of string to be displayed
# this will be the width of the image
$y = $font_height; # height of image in pixels
$image = new GD::Image($x, $y); # create an image of that width and height
# allocate some colors
$white = $image->colorAllocate(255, 255, 255); # white
$blue = $image->colorAllocate(0, 0, 255); # blue
$image->transparent($white); # make the gif transparent
$image->string(gdLargeFont, 0, 0, $counter, $blue); # print the counter
print $image->gif; # print the image to STDOUT
$location. 3. Finally, insert a call to this script in the page.
4. Try it.tucotuco.cs.indiana.edu% vi index.html tucotuco.cs.indiana.edu% pwd /nfs/paca/home/user2/dgerman/httpd/htdocs tucotuco.cs.indiana.edu% cat index.html <html> <head> <title> Home Page </title> </head> <body bgcolor=white> <h1>Welcome!</h1> This page has been accessed <img src="/cgi-bin/homepage"> times. </body> </html> tucotuco.cs.indiana.edu%
In my case: http://tucotuco.cs.indiana.edu:198005. (Minor) Caveats.(Use your own server and port number).
The counter is increased every time the script is accessed.The script can be called outside the page so the value of the counter is only approximately correct and the counter is an indirect way of counting accesses to the page.
A better solution is to use frames and have one of the frames' source be the output of a script. The script can output the value of the counter as part of the virtual document, because it has complete control over it.
Graphical counters such as the one discussed in this lab are only exercises in using libraries such as GD.pm and they provide the functionality (web counter) when the document delivered is in a static file, and the delivery is done by the server, so no script is involved.
B. Graphical Clock.
Put this script in httpd/cgi-bin/clock amd make it
executable. Study the code and add numbers to the clock dial.
#!/usr/bin/perl
use GD; print "Content-type: image/gif\n\n";
($seconds, $minutes, $hour) = localtime(time);
$x = $y = 100; $R = $x / 2; $twopi = 2 * 3.141592;
$dhx = $R * sin($hour / 12 * $twopi); # [1]
$dhy = $R * cos($hour / 12 * $twopi); # [2]
$dmx = $R * sin($minutes / 60 * $twopi);
$dmy = $R * cos($minutes / 60 * $twopi);
$dhy = - $dhy; # mirror
$dhy *= 0.66; $dhx *= 0.66; # scale
$dhx += $R; $dhy += $R; # translate
$ox = $R; $oy = $R; # translate origin
$dmy = - $dmy; # mirror
$dmx += $R; $dmy += $R; # translate
$image = new GD::Image($x, $y);
$black = $image->colorAllocate(0, 0, 0);
$yellow = $image->colorAllocate(255, 255, 0);
$image->line($ox, $oy, int($dmx), int($dmy), $yellow);
$image->line($ox, $oy, int($dhx), int($dhy), $yellow);
$image->arc($R, $R, 2 * $R, 2 * $R, 0, 360, $yellow);
print $image->gif;
exit(0);
A question was raised in class yesterday about the way we were ending our pattern. Specifically our pattern was not general enough because it was not catching URLs that had in their descriptive names HTML tags, such as <font></font> <br> <h1></h1> and the like. I include a modification of the program below for two reasons:
#!/usr/bin/perl
open (AB, "/u/dgerman/httpd/htdocs/benchmark.html");
@x = <AB>;
$x = join('', @x);
while # ($x =~ s/(<a\s+href)//i) {
# ($x =~ s/(<a\s+href\s*=)//i) {
# ($x =~ s/(<a\s+href\s*=\s*"[^"]+")//i) {
# ($x =~ s/(<a\s+href\s*=\s*"[^"]+"\s*>)//i) {
# ($x =~ s/(<a\s+href\s*=\s*"[^"]+"\s*>.*?<\/a>)//is) {
# ($x =~ s/<a\s+href\s*=\s*"([^"]+)"\s*>.*?<\/a>//is) {
print $i++, ". ", $1, "\n";
}
close(AB);