CSC 3530 Software Technology Tutorial Two PERL Basics

CSC 3530 Software Technology Tutorial Two PERL Basics

PERL Basics Practical Extraction and Report Language It is interpreted (no need to compile) Java is something in between, both compile and interpreted Syntax similar to C language Loosely typed language No type like int, double, char, BOOL Why Perl for CGI? For the same CGI program, Perl is much shorter than C

Simple Example #!usr/bin/perl –w # this is a simple hello program print ‘Hi, I am computer. What’s your name? ’; $name=<STDIN>; chomp $name; print “Hi $name, nice to meet youn”; exit(0); #!usr/bin/perl –w Location of perl interpreter, use whereis perl to get it -w switch to enable warning Place your comment after # All statements end with ;

Cont’d print – function to print strings to standard output (monitor) $name – all scalar variables in perl start with $ <STDIN> - read input from standard input (keyboard) <FILE> - file handle to read input from file, will be described later chomp – function to remove new line character (n) exit – end the program

Properties of Perl Function call may or may not need () No main function Do not need to declare variable at first Strings are enclosed by “” or ‘’ “” will try to evaluate variable inside e. g. “Hi, $name” while ‘Hi, $name’ will not This is call variable interpolation +, -, *, /, % similar to C ** means to the power of, e. g. $eight=2**3; # $eight will be 8

Boolean in Perl Things in Perl that considered as false Number zero Empty string String zero Undefined $false=0; $false=“”; $false=“ 0”; $false; Comparison ==, >, <, >=, <=, !=, eq, gt, lt, ge, le, ne Logical operator &&, ||, !, and, or, not Short circuit open (FH, ”file. txt”) || die “cannot open file” If file open is successful, the later statement will not be executed, otherwise, it will be executed and program terminated

Array in Perl start with @ e. g. @terms=(‘RSA’, ’DES’, ’OLAP’, ’OSI’, ’Middleware’); for ($i=0; $i<=$#terms; $i++) { print “$terms[$i] ”; } Output: > RSA DES OLAP OSI Middleware $terms[$i] – the (i+1)th element, array in perl counts from 0 $#terms returns the index of the last element in the array Can be replace by @terms=qw(RSA DES OLAP OSI Middleware); qw is a function : quote word

Cont’d Another way to do this @terms=qw(RSA DES OLAP OSI Middleware); foreach $item(@terms) { print “$item “; } # more straight forward foreach (@terms) { print “$_ “; } Both are the same, $_ is a special variable, many functions use it as default parameter, we will talk about this later, perhaps

Flow of Control Most are similar to C if (condition) {statement} else {statement} while (continuing condition) {statement} for (A; B; C) {statement} A – initialization B – continuing condition C – statement to be executed every iteration Breaking the loop last – similar to break in C next – similar to continue in C

Cont’d Two examples while ($i<15) { last if ($i==7); $i++; } # $i in here equal 7; for ($i=0; $i<100; $i++) { next if (not $i % 2); print “An odd number =$in”; #only odd number goes here }

FILE I/O Simple file copy program #!/usr/bin/perl –w open(SOURCE, ‘c: \sourcefile. txt’) || die ‘Cannot open source’; open(DEST, ’>c: \destfile. txt’) || die ‘Cannot open dest’; @contents=<SOURCE>; #read all the lines into array print DEST @contents; #print all the lines close(SOURCE); close(DEST); #can be shorter, replace 2 lines by: print DEST <SOURCE>; > sign is to indicate we want to write something to this file @contents=<SOURCE> is a little bit lazy, you may use a for loop instead print DEST @contents is to print all lines to the DEST file handle, if we omit it, the default is STDIN (monitor)

Hash structure Hash is like a table lookup e. g. telephone directory Hash structure begins with % Dickson 26098402 Richard 26098403 Nelson 26098431 %name=(‘ 3530’, ‘software technology’, ‘ 5280’, ‘image processing’, ‘ 5110’, ‘advance software eng. ’); print “ 3530: $name{‘ 3530’}n”; print “ 5280: $name{‘ 5280’}n”; Output: 3530: software technology 5280: image processing {‘ 3530’} Course codes are key, while course names are values Key value pair can be added dynamically $name(‘ 5180’)=‘data mining’; #a key value pair is added

More about hash print “We have these keys in our hash tablen”; foreach $key (keys %name) { print “$keyn”; } print “We have these values in our hash tablen”; foreach $value (values %name) [ print “$valuen”; } If (exists $name{‘ 5120’}) { print “we have key 5120 in the hash tablen”; } else { ` print “we do not have key 5120 in the hash tablen”; } #correct ways to check whether the key, value pair exist

Split, Join Given a query string, How to retrieve the value input by user? ID=LJ 4000&Category=printer&Price=700 $string=$ENV{‘QUERY_STRING’}; #get the query string @pair=split(/&/, $string); for each(@pair) { ($name, $value)=split(/=/, $_); print “$name = $valuen”; } Output: ID = LJ 4000 Category = printer Price = 700 Join will be discussed later in this tutorial

Functions (sub-routine) Perl allow recursion Functions in perl are defined like: sub function_name { statements; } Argument stored in @_ (a special array variable) You do not need to specify the number of argument Handle this carefully, you should know what you are doing Argument are all passed by reference Better use my to declare local variable

More about function sub mean { my (@data)=@_; my $sum; foreach (@data) { $sum+=$_; } return ($sum/@data); } sub compare { my ($a, $b)=@_; if ($a>$b) { return (1); } elseif ($a<$b) { return (-1); } else { return (0); } } # my – indicate a local variable # a way to retrieve parameters

Basic CGI We will introduce a perl CGI example that enable you to get values from a form and manipulate. www 2. cse. cuhk. edu. hk/~csc 3530/student_data. htm, use proxy. cse. cuhk. edu. hk and port 8000 use view source to check HTML code Name: id Name: name Name: major Name: level Name: csc 1500, csc 2510, csc 2520

Simple example #!/usr/local/bin/perl 5 -w use CGI qw(: standard); # use the CGI module use strict; # variable declaration more strict sub no_input { print header(); # Content-type: …. . print start_html('Error'); print qq(<p>No input parameter</p>); print end_html(); } if (!param) { # check input parameter no_input; } else { my $id=param('id'); my $name=param('name');

Cont’d my $major=param('major'); my $level=param('level'); my $csc 1500=param('csc 1500'); my $csc 2510=param('csc 2510'); my $csc 2520=param('csc 2520'); # get values open (STAT, ">>/uac/cprj/csc 3530/www/cgi-bin/stat. txt"); my $data=join (', ', ($id, $name, $major, $level, $csc 1500, $csc 2510, $csc 2520)); print STAT "$datan"; close (STAT); print header(); print start_html('Statistic'); print qq(<p>Thanks for your support!</p>); print end_html(); }

Next Week Issues on making CGI to work Servers in CSE In depth discussion of CGI programming Example similar to project Supplier database SQL – (may be) insert, update, select