M.P. Johnson, DBMS, Stern/NYU, Spring C : Database Management Systems Lecture #20 M.P. Johnson Stern School of Business, NYU Spring, 2005

M.P. Johnson, DBMS, Stern/NYU, Spring 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 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 Goals: after this week Understand dynamic webpages 1. CGI 2. 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 Perl 2. In PHP that 1. That do look-ups with user-entered parameters 2. And display the results 3. Based on examples from class

M.P. Johnson, DBMS, Stern/NYU, Spring 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 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 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 url 2.  webserver runs that url’s program, 3. sends back the program’s output

M.P. Johnson, DBMS, Stern/NYU, Spring On-the-fly content with CGI Program Client Server HTTP Request Data for program Generated HTML HTML Image from

M.P. Johnson, DBMS, Stern/NYU, Spring Using CGI CGI works with any prog./scripting lang. Really? Well, no, not really…

M.P. Johnson, DBMS, Stern/NYU, Spring 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 CGI admin Most webservers: CGI program/script must either 1. End in.cgi and/or 2. 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 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 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 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. perl/lookup.cgi perl/lookup.cgi

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

M.P. Johnson, DBMS, Stern/NYU, Spring hello.pl Hello, World - hello.pl Running at command prompt: #!/usr/bin/perl -w print "Hello World\n"; #!/usr/bin/perl -w print "Hello World\n"; sales% perl hello.pl Hello World sales% sales% perl hello.pl Hello World sales%

M.P. Johnson, DBMS, Stern/NYU, Spring Hello, World - hello.pl Run from browser:  What’s wrong?  What’s wrong?  What’s wrong?

M.P. Johnson, DBMS, Stern/NYU, Spring Troubleshooting hello.cgi 1. 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.cgi sales% chmod +x hello.cgi sales%./hello.cgi sales% chmod +x hello.cgi sales% cp hello.pl hello.cgi

M.P. Johnson, DBMS, Stern/NYU, Spring Troubleshooting hello.cgi 5. Make sure you’re printing the HTML header #! /usr/bin/perl -w print "Content-type: text/html\n\n"; print "Hello World\n"; #! /usr/bin/perl -w print "Content-type: text/html\n\n"; print "Hello World\n";

M.P. Johnson, DBMS, Stern/NYU, Spring Troubleshooting hello.cgi 5.Show errors and warnings:  Is case-sensitive #! /usr/bin/perl -w use CGI qw(:standard); use CGI::Carp qw( fatalsToBrowser warningsToBrowser ); print header(); pr int "Hello World\n"; #! /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 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 Perl, HTML, and CGI.pm CGI.pm offers a “front-end” to HTML  Replaces mark-up language with an API Very simple example:  gipm.pl gipm.pl  gipm.cgi gipm.cgi Somewhat simpler, but another thing to learn Mostly won’t cover Review: Hello, World

M.P. Johnson, DBMS, Stern/NYU, Spring 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 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 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 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"; my $query = "select …"; my $s = "hi"; $s = 10; $s = 3.5; my $s = "hi"; $s = 10; $s = 3.5;

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

M.P. Johnson, DBMS, Stern/NYU, Spring Tutorials on Perl Some material drawn from the following good tutorials: CGI backend programming using perl:  Perl Basics:  CGI Basics:  MySQL/Perl/CGI example: 

M.P. Johnson, DBMS, Stern/NYU, Spring Tutorials on PHP Some material drawn from the following good tutorials: PHP introduction and examples:  Interactive PHP with database access:  Longer PHP/MySQL Tutorial from webmonkey:  Nice insert/update/delete example from webmonkey:  MySQL/Perl/PHP page from U-Wash: 

M.P. Johnson, DBMS, Stern/NYU, Spring For next time… 1. Go through at least one tutorial each on Perl and PHP 2. Try posting a hello-web Perl script in your sales account 3. Run/read these: