C20.0046: Database Management Systems Lecture #20

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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C20.0046: Database Management SystemsLecture #20

M.P. JohnsonStern School of Business, NYUSpring, 2005

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Homework Project part 4 due Thursday

Topic: populating your tables with data Using MySQL’s bulk loader Start early! Turn in on time

Project part 5 Topic: web interface + any remaining loose ends Assigned after Thursday Due: end of semester

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Agenda: Programming for SQL Have now been exposed to:

Embedded SQL: Pro*C Java JDBC Stored Procedures: PL/SQL

All used; good to know about

Most important for this course: DB-conn from web scripting languages DBI/DBDs in Perl, PHP

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Goals: after this week Understand dynamic webpages

1. CGI2. PHP-like scripting

Today: be able to post a hello-web Perl program in your sales account

This week: Be able to write simple dynamic webpages in

1. In Perl2. In PHP

that1. That do look-ups with user-entered parameters2. And display the results3. Based on examples from class

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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New topic: web apps Goal: web front-end to database

Present dynamic content, on demand Not canned (static) pages/not canned queries (perhaps) modify DB on demand

Naïve soln: static webpage & HTTP index.html written, stored, put on server, displayed

when it’s url is requested HTTP is stateless (so?) This doesn’t solve our problem

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Dynamic webpages Soln 1: upon url request

1. somehow decide to dynamically generate an html page (from scratch)

2. send back new html page to user

No html file exists on server, just created on demand

CGI/Perl, Java servlets, etc.

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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New topic: CGI First, and still very popular method CGI: Common Gateway Interface

Not a programming language! Just an interface (connection) between the

webserver and an outside program “Webserver” = webserver software, e.g., Apache

Very simple basic idea:1. user chooses an url22 webserver runs that url’s program,3. sends back the program’s output

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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On-the-fly content with CGI

ProgramClient

Server

HTTP Request

Data for program

Generated HTML

HTML

Image from http://www.scit.wlv.ac.uk/~jphb/cp3024/

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Using CGI CGI works with any prog./scripting lang.

Really?

Well, no, not really…

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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CGI works… if the webserver machine can run program

pages/soho, not sales and if the user the webserver is running as

(e.g. nobody) can can run your program and if the necessary jars/libraries are

available and if nobody has permission to use them and if the necessary DB software is installed

Plausible choices: Perl, Python, C, sh

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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CGI admin Most webservers: CGI program/script must

either1. End in .cgi and/or2. Reside in cgi-bin

Ours: needs .cgi extension If an actual program, the cgi file is just the

name of the executable:

gcc -o myprog.cgi myproc.gcc

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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CGI admin In a script, first (“shebang”) line says which

interpreter to use:

Either way, cgi file must be executable:

Make sure your cgi file runs at cmd prompt:

But not a guarantee!

#!/usr/local/bin/perl

sales% chmod +x *.cgi

sales% ./myprog.cgi

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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CGI input CGI programs must respond to input Two mechanisms:

GET: read env. var. QUERY_STRING POST: get length from env. var.

CONTENT_LENGTH; read from STDIN This diff. mostly invis. to Perl, PHP Both send a sequence of name/value pairs,

separated by &s:

name=a&submit=Search

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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CGI input Appearance/security differences GET: string is part of the URL, following a ?:

POST: string can be read by program from an environmental variable Vars not visible to the browser user Not automatically put in server log, etc.

http://pages.stern.nyu.edu/~mjohnson/dbms/perl/lookup.cgi

http://google.com

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Our use of CGI We’ll discuss CGI and Perl

One option for your project Can try C, C++, etc. But not recommended!

For CGI, only Perl will be “supported” Scripting languages v. programming languages Development v. IT Other languages are still not recommended

especially if you don’t know Perl and PHP

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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New topic: Just Enough Perl Very popular, powerful scripting language Very good at “regular expressions”, text manipulation,

but not very relevant to us

Instead: simple text/html production Basic language constructs MySQL connectivity

Perl = Practical Extraction and Report Language= Pathologically Eclectic Rubbish Lister

perl -pi -e 's/tcsh/sh/' $HOME/.login

See http://perl.org.il/pipermail/perl/2003-February/001047.html

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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hello.pl Hello, World - hello.pl

Running at command prompt:

#!/usr/bin/perl -w

print "Hello World\n";

sales% perl hello.plHello Worldsales%

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Hello, World - hello.pl Run from browser:

http://pages.stern.nyu.edu/~mjohnson/dbms/perl/hello.pl

What’s wrong? http://pages.stern.nyu.edu/~mjohnson/dbms/perl/hello.cgi

What’s wrong? http://pages.stern.nyu.edu/~mjohnson/dbms/perl/hello2.cgi

What’s wrong?

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Troubleshooting hello.cgi1. Get the extension right:

2. Try running with perl: Are there Perl errors?

3. Try running as program: Are the execute permissions on?

sales% perl hello.cgi

sales% ./hello.cgisales% chmod +x hello.cgi

sales% cp hello.pl hello.cgi

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Troubleshooting hello.cgi5. Make sure you’re printing the HTML header

#! /usr/bin/perl -w

print "Content-type: text/html\n\n";

print "Hello World\n";

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Troubleshooting hello.cgi5. Show errors and warnings:

http://pages.stern.nyu.edu/~mjohnson/dbms/perl/hello3.cgi Is case-sensitive

#! /usr/bin/perl -w

use CGI qw(:standard);use CGI::Carp qw( fatalsToBrowser

warningsToBrowser );

print header();pr int "Hello World\n";

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Perl and HTML headers Data sent to a browser is prefaced with a

header describe type of data:

Hand-generated html must print this before anything else:

Or: When use-ing CGI

Content-type: text/html\n\n

print "Content-type: text/html\n\n";

print CGI::header();

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Perl, HTML, and CGI.pm CGI.pm offers a “front-end” to HTML

Replaces mark-up language with an API

Very simple example: http://pages.stern.nyu.edu/~mjohnson/dbms/perl/

cgipm.pl http://pages.stern.nyu.edu/~mjohnson/dbms/perl/

cgipm.cgi

Somewhat simpler, but another thing to learn Mostly won’t cover Review: Hello, World

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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More on Perl Perl is mostly “C-like” Perl is case-sensitive Use # for rest-of-line comments Creation of functions is supported but optional

Like PL/SQL Perl has “modules”/“packages” CGI module:

Provides header() function, easy access to CGI params Mysql module:

use CGI qw(:standard);

use Mysql;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Perl and strings Can use “ ” for strings Concatenate with . op:

Print text with print function:

Or, parentheses can be dropped!

“Hi ” . “there\n”

print (“Hi there”);

print “Hi there”;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Perl and strings Can compare numbers (as numbers) with

usual operators < > <=, etc. 3 < 5

These do not apply to strings String ops are based on initials of operations:

eq, ne, lt, gt, le, ge “hi” ne “there” “hi” le “hi there”

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Perl and variables All regular variables begin with $

$input, $query Declare vars with my:

Q: What about var types? A: Perl is loosely typed!

my $s = "hi";my $query = "select …";

my $s = "hi";$s = 10;$s = 3.5;

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Perl, strings, and variables print takes var-many arguments:

Variables are always “escaped”

Vars may appear within strings:

Prints out: Hello Dolly. To prevent escaping, use single quotes '$name‘

$name = "Dolly";

print ("Hello $name.\n");

print ("Hello ", "Dolly", ".\n");

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Perl syntax examples Access member/field of object ::

object::member Access member pointed to by object ->

rowhash->field Can access array members with indices Can access hash members with strings

http://pages.stern.nyu.edu/~mjohnson/dbms/perl/controls.cgi http://pages.stern.nyu.edu/~mjohnson/dbms/perl/controlscgi.txt

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Tutorials on Perl Some material drawn from the following good tutorials: http://perl.com

CGI backend programming using perl: http://www.scit.wlv.ac.uk/~jphb/sst/perl/

Perl Basics: http://www.cs.wcupa.edu/~rkline/Perl/perl-basics-1.html

CGI Basics: http://www.cs.wcupa.edu/~rkline/Perl/cgi-basics-1.html

MySQL/Perl/CGI example: http://www.scit.wlv.ac.uk/~jphb/sst/perl/ex3d.html

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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Tutorials on PHP Some material drawn from the following good tutorials: http://php.net

PHP introduction and examples: http://www.scit.wlv.ac.uk/~jphb/sst/php/

Interactive PHP with database access: http://www.scit.wlv.ac.uk/~jphb/sst/php/gazdb.html

Longer PHP/MySQL Tutorial from webmonkey: http://hotwired.lycos.com/webmonkey/99/21/index2a.html

Nice insert/update/delete example from webmonkey: http://hotwired.lycos.com/webmonkey/99/21/index3a.html

MySQL/Perl/PHP page from U-Wash: http://www.washington.edu/computing/web/publishing/mysql-script.html

M.P. Johnson, DBMS, Stern/NYU, Spring 2005

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For next time…1. Go through at least one tutorial each on Perl and

PHP2. Try posting a hello-web Perl script in your sales

account

3. Run/read these:

http://pages.stern.nyu.edu/~mjohnson/dbms/perl/controls.cgi http://pages.stern.nyu.edu/~mjohnson/dbms/perl/controlscgi.txt

http://pages.stern.nyu.edu/~mjohnson/dbms/perl/lookup.cgi http://pages.stern.nyu.edu/~mjohnson/dbms/perl/lookupcgi.txt