04-08-2011
I don't think there's much mysterious about it. Someone writes a language and people like it and its use begins to spread.
A web server can run programs from whatever programming language you desire through its CGI backend -- person retrieving webpage causes apache to execute the program /var/www/localhost/cgi-bin/my-fancy-program and send the program's stdout output to the person's web-browser raw. You can even write a web program as a plain Bourne shell script and it's a bit illuminating to do so -- you can see where all the data comes from, with server variables as environment variables and POST data fed into your program's standard input (if memory serves) and no commandline arguments whatsoever. Someone at the university was silly enough to write the school's web-based scheduling system in prolog of all things, and the server couldn't handle the strain...
The only thing that differentiates a Web Development language from any other language, I think, is built-in features which make communicating with the CGI (Common Gateway Interface) easier. You can insert PHP code inside HTML for one thing -- it still has to be processed on the server-side, of course, but having your webpage and your web code in the same document is something that's awkward or impossible in many other languages.
PHP also slurps up all the POST output and relevant server variables into its own special variables for your convenience and comes with many more features besides for communicating with web servers and web clients. You can print all the text needed to set up a cookie with a few library calls and so forth. They've also improved its performance by integrating it more tightly with the web server so it doesn't need to run a fresh copy of PHP every time. They didn't have to do that, it was just advantageous to do so.
And even though it's a Web Development language, PHP can still be used for other purposes, even on the commandline. Because of the way you can insert PHP inside other text documents inside <?php program_code(); ?> tags, I've occasionally found it useful for templates.
Last edited by Corona688; 04-08-2011 at 10:58 AM..
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LEARN ABOUT DEBIAN
polipo
POLIPO(1) General Commands Manual POLIPO(1)
NAME
polipo - a caching web proxy
SYNOPSIS
polipo [ -h | -v | -x ] [ -c config ] [ var=val ]...
DESCRIPTION
Polipo is a caching HTTP proxy. It listens to requests for web pages from your browser and forwards them to web servers, and forwards the
servers' replies to your browser. In the process, it optimises and cleans up the network traffic.
By default, Polipo listens on TCP port 8123. Please configure your web browser to use the proxy on localhost port 8123.
OPTIONS
-h Display help and exit.
-v Display the list of configuration variables and exit.
-x Purge the on-disk cache and exit.
-c Select an alternate configuration file.
var=val
Change the value of a configuration variable.
FILES
/etc/polipo/config
The default location of Polipo's configuration file.
/etc/polipo/forbidden
The default location of the list of forbidden URLs.
/var/cache/polipo/
The default location of the on-disk cache.
/usr/share/polipo/www/
The default root of the local web space.
SIGNALS
SIGUSR1
write out all in-memory objects to disk and reload the forbidden URLs file.
SIGUSR2
write out all in-memory objects to disk, discard all in-memory objects, and reload the forbidden URLs file.
SIGTERM, SIGINT, SIGHUP
write out all in-memory objects to disk and quit.
SECURITY
The internal web server will follow symbolic links that point outside the local document tree. You should run Polipo in a chroot jail if
that is a problem.
There is no reason to run Polipo as root.
FULL DOCUMENTATION
The full manual for Polipo is maintained in a texinfo file, and is normally available through a web server internal to Polipo. Please make
sure that Polipo is running, and point your favourite web browser at
http://localhost:8123/
Alternatively, you may type
$ info polipo
at a shell prompt, or
C-h i m polipo RET
in Emacs.
AUTHOR
Polipo was written by Juliusz Chroboczek.
POLIPO(1)