Introduction to Programming the WWW I CMSC Summer 2004 Lecture 13

2 Today’s Topics CGI module Patterns and regular expression

3 Perl Modules A Perl module is a self-contained piece of Perl code that can be used by a Perl program or by other Perl modules  Conceptually similar to a C link library, or a C++ class  Perl 5 module list Perl 5 module list Each Perl module has a unique name  Perl provides a hierarchal name space for modules  Components of a module name are separated by double colons (::)  Example: CGI Math::Complex

4 Perl Modules (cont’d) Each module is contained in a single file  Module files are stored in a subdirectory hierarchy that parallels the module name hierarchy  All module files have an extension of.pm  Example: Math::Complex is stored in Math/Complex.pm Finding module libraries  The Perl interpreter has a list of directories in which it searches for modules. This list is available in the global  Use perl –V to see the initial contents Local modules vs. modules coming from standard distribution CGI stored in /opt/perl/perl /lib/ /CGI.pm Math::Complex is actually stored in /opt/perl/perl /lib/ /Math/Complex.pm

5 Using Perl Modules Modules must be imported in order to be accessible to a script  This is done with the use function  use statements are commonly made at the beginning of a program or subroutine This makes it easier to understand the program and see which modules are loaded.  Example: use Math::Complex; use CGI “:standard”; A modifier to a module

6 Using CGI.pm to generate HTML The CGI.pm module provides several functions that can be used to concisely output HTML tags For example, $mypage=‘It is a New Day’; print “ $mypage ”; can also be written as: $mypage=’It is a New Day’; print start_html(‘$mypage’);

7 3 Basic CGI.pm Modules header  creates the MIME Content-type line start_html  creates starting HTML tags end_html  creates ending HTML tags 1. #!/usr/local/bin/perl 2. use CGI ‘:standard’; 3. print header; 4. print start_html; 5. print ' '; 6. print 'Welcome humans to my site '; 7. print end_html;

8 CGI.pm Basic Functions The various CGI/PM function accept 3 basic syntactic formats:  No argument format functions that can be used without any arguments  Positional argument format functions that can accept comma-separated arguments within parentheses  Name-value argument format functions that accept parameters submitted as name- and-value pairs

9 No Argument Format The Previous Example shows the start_html, header, end_html functions You can place the 1 or more functions directly within a print statement  Would output

10 Some Single Argument Functions CGI.pm Function Example of UseExample Output header - the MIME Content-type line print header;Content- type:text/html\n\n start_html — Tags to start an HTML document print start_html; br —output tag print br; hr —generate horizontal rule print hr; end_html —end an HTML document print end_html;

11 Positional Argument Format Specify multiple arguments based on the position of the argument For example would output Hello World

12 Some Positional Functions CGI.pm Functions Example of UseExample Output start_html() — tags needed to start an HTML document. start_html(‘My Page’); My Page h1() —header level 1 tags. (also h2(), …, h6() ) print h1(‘Hello There’); Hello There strong() – output argument in strong. print strong('Now'); Now p() —creates a paragraph. print p(‘Time to move’); Time to move b() —prints the argument in bold. print b('Exit'); Exit i() —prints the argument in italics. Print i('Quick'); Quick

13 Operating on Variables Can concisely use functions with a single print statement:  print i('Please '),'come when I call you ', strong('immediately.'); This code would output the following:  Please come when I call you immediately.

14 Consider the following example: 1. # !/usr/local/bin/perl 2. use CGI ':standard'; 3. print header, start_html(‘Positional Example’), h1('Simple Math'); 4. print b('two times two='), 2*2; 5. print br, 'but ', b('four times four='), 4*4; 6. print br, 'Finally, ', b('eight times eight='), 8*8; 7. print end_html;

15 Name-Value Argument Format Can specify names and values as follows: Would output the following: My Title

16 Some name/value functions CGI.pm Function Example UsageExample Output start_html start HTML document print start_html({ -title=>‘my title’, –bgcolor=>’red’ }); my title img —inserts an image print img({- src=>'myfile.gif', -alt=>’picture’}); a —establishes links print a({ -href =>' 'Click Here'); Click Here font() — creates … tags print font( { -color=>‘BLUE’, –size=> ’4’}, ‘Lean, and mean.’); Lean, and mean.

17 Example Name/Value Program 1. #!/usr/local/bin/perl 2. use CGI ':standard'; 3. print header; 4. print start_html({-title=>'New Day ', -bgcolor=>'yellow'}); 5. print 'Welcome One And ', i('All'); 6. print end_html;

18 Using CGI.pm with HTML forms CGI.pm Function Example UsageExample Output start_form start HTML form element print start_form({ -method=>‘post’, –action=> ‘ freis/cgi-bin/reflector.pl’}); textfield, password_field —inserts a text field or password field print textfield(- name=>'textfield1', -size=>'50', -maxlength=>'50'); scrolling_list —insert a multiple list print scrolling_list(-name=>'list1', -values=> ['eenie', 'minie', 'moe'], -default=> ['eenie','moe'], -size=>5, -multiple=>'true'); eenie minie moe textarea — inserts a text area print textarea(-name=> 'large_field_name', -rows=> 10, -columns=>50);

19 Using CGI.pm with HTML forms (cont’d) CGI.pm Function Example UsageExample Output checkbox_group – insert checkbox print checkbox_group(-name=> 'color', -values=>['red ','orange ','yellow '], -default=>['red ']); red orange yellow raidio-group — inserts a text field print radio_group(-name=>'color blind', -values=>['Yes','No'], - default=>'No'); Yes No submit,reset —insert a submit or reset button print submit('submit', 'Submit'); Print reset; endform — print end form tag print endform(); Perl CGI Reference

20 A CGI Form Example

21 Receiving HTML Form Arguments Within the CGI program call param() function  Input variables into CGI/Perl programs are called CGI variables Values received through your Web server as input from a Web browser, usually filled in a form  To use param():

22 Receiving HTML Form Arguments

23 Sending Arguments You can send arguments to your CGI program directly from the URL address of a browser _checker.cgi?color=red

24 Sending Multiple Arguments Precede first argument with ? Precede next argument with &

25 Debug CGI Program in Command Line To start and send an argument to the password program can execute the following: perl cgiform1_checker.cgi color=red Enclose blank spaces or multiple arguments in quotation marks: perl cgiform1_checker.cgi ‘color=rose red’ perl cgiform1_checker.cgi 'color=red&secret=none'

26 Check CGI Variables Values Perl provides a simple method to test if any parameters were received or null: $var = param(‘some_cgi_variable’) ; if ($var) { statement(s) to execute when $var has a value } else { statement(s) to execute when $var has no value }

27 Combining Program Files Applications so far have required two separate files; one file for to generate the form, and the other to process the form  Example: cgiform1.cgi and cgiform1_checker.cgi  Can test return value on param() to combine these At least two advantages  With one file, it is easier to change arguments  It is easier to maintain one file

28 Combining Program Files

29 CGI Module: Advanced Topic* Functional(procedural) Orientation  use CGI ‘:standard’; Object Orientation  use CGI;  Call new() operator to create a CGI object and stores in a variable. The functions of CGI.pm are accessed through the -> operator with the object variable at the left side $q = new CGI; print $q->header();  004/winter/ /02/perl/perl_index.html 004/winter/ /02/perl/perl_index.html

30 Several Resources URL  /2004/winter/ /02/perl/perl_index.html /2004/winter/ /02/perl/perl_index.html Topics  How to write your first CGI script How to write your first CGI script  Checking CGI Parameters on the Command Line Checking CGI Parameters on the Command Line  Server-side Validation Server-side Validation  Hidden HTML Form Fields Hidden HTML Form Fields  Sorting with Perl Sorting with Perl

31 Patterns in String Variables Many programming problems require matching, changing, or manipulating patterns in string variables.  An important use is verifying input fields of a form helps provide security against accidental or malicious attacks. For example, if expecting a form field to provide a telephone number as input, your program needs a way to verify that the input comprises a string of seven digits.

32 Four Different Constructs Will look at 4 different Perl String manipulation constructs:  The match operator enables your program to look for patterns in strings.  The substitute operator enables your program to change patterns in strings.  The split function enables your program to split strings into separate variables based on a pattern. (already covered)  Regular expressions provide a pattern matching language that can work with these operators and functions to work on string variables.

33 The Match Operator The match operator is used to test if a pattern appears in a string.  It is used with the binding operator (“ =~ ”) to see whether a variable contains a particular pattern.

34 Possible Values of $name

35 Using Character Class Matching any one in a set of characters enclosed within square brackets  foo[bc]ar will match foobar and foocar Ranges can be expressed inside of a character class by using a dash between two characters  [a-g] is equal to [abcdefg]  [0-9] is equal to any digit  [a-zA-Z] Negative character class: use the caret (^) symbol as the first thing in the character class  a[^bc]d, [^0-9]

36 Other Delimiters? Slash (“/”) is most common match pattern  Others are possible, For example, both use valid match operator syntax:  if ( $name =~ m!Dave! ) {  if ( $name =~ m ) { The reverse binding operator test if pattern is NOT found: if ( $color !~ m/blue/ ) { Demo

37 The Substitution Operator Similar to the match operator but also enables you to change the matched string.  Use with the binding operator (“ =~ ”) to test whether a variable contains a pattern

38 How It Works Substitutes the first occurrence of the search pattern for the change pattern in the string variable. For example, the following changes the first occurrence of t to T : $name = “tom turtle”; $name =~ s/t/T/; print “Name=$name”; The output of this code would be Name=Tom turtle

39 Changing All Occurrences You can place a g (for global substitution) at the end of the substitution expression to change all occurrences of the target pattern string in the search string. For example,  $name = “tom turtle”;  $name =~ s/t/T/g;  print “Name=$name”; The output of this code would be  Name= Tom TurTle Demo

40 Using Translate A similar function is called tr (for “translate”). Useful for translating characters from uppercase to lowercase, and vice versa.  The tr function allows you to specify a range of characters to translate from and a range of characters to translate to. : $name="smokeY"; $name =~ tr/[a-z]/[A-Z]/; print "name=$name"; Would output the following Name=SMOKEY

41 A Full Pattern Matching Example 1. #!/usr/local/bin/perl 2. use CGI ':standard'; 3. print header, start_html('Command Search'); 'XX1234', 'XX1892', 'XX9510'); 5. $com=param('command'); 6. $prod=param('uprod'); 7. if ($com eq "ORDER" || $com eq "RETURN") { 8. $prod =~ s/xx/XX/g; # switch xx to XX 9. if ($prod =~ /XX/ ) { 10. foreach $item ) { 11. if ( $item eq $prod ) { 12. print "VALIDATED command=$com prodnum=$prod"; 13. $found = 1; 14. } 15. } 16. if ( $found != 1 ) { 17. print br,"Sorry Prod Num=$prod NOT FOUND"; 18. } 19. } else { 20. print br, "Sorry that prod num prodnum=$prod looks wrong"; 21. } 22. } else { 23. print br, "Invalid command=$com did not receive ORDER or RETURN"; 24. } 25. print end_html;

42 Would Output The Following...

43 Using Regular Expressions regular expressions to enable programs to match patterns more completely.  They actually make up a small language of special matching operators that can be employed to enhance the Perl string pattern matching.

44 The Alternation Operator Alternation operator looks for alternative strings for matching within a pattern.  (That is, you use it to indicate that the program should match one pattern OR the other). The following shows a match statement using the alternation operator (left) and some possible matches based on the contents of $address (right); this pattern matches either com or edu.

45 Example Alternation Operator

46 Parenthesis For Groupings You use parentheses within regular expressions to specify groupings. For example, the following matches a $name value of Dave or David.

47 Special Character Classes Perl has a special set of character classes for short hand pattern matching For example consider these two statements if ( $name =~ m/ / ) { will match $name with embedded space char if ($name =~ m/\s/ ) { will match $name with embedded space, tab, newline

48 Special Character Classes

49 Special Character Classes - II

50 Special Character Classes - III

51 Setting Specific Patterns w/ Quantifiers Character quantifiers let you look for very specific patterns For example, use the dollar sign (“ $ ”) to to match if a string ends with a specified pattern. if ($ Name =~ /Jones$/ ) { Matches “John Jones” but not “Jones is here” would not. Also, “The guilty party is Jones” would matches.

52 Selected Perl Character Quantifiers I

53 Selected Perl Character Quantifiers II

54 Selected Perl Character Quantifiers III

55 Match the Special Characters Themselves Use a back slash before the special character  \^, \$, \., \?, \(, \), \+, \*,\\,\/ etc  Examples Will a\??bc matches abc, a?bc Will a\++bc matches a+bc, a++bc

56 Building Regular Expressions That Work Regular expressions are very powerful— but they can also be virtually unreadable.  When building one, tart with a simple regular expression and then refine it incrementally. Build a piece and then test  The following example will build a regular expression for a date checker dd/mm/yyyy format (for example, 05/05/2002 but not 5/12/01 ).

57 1. Determine the precise field rules. - What is valid input and what is not valid input?  E.g., For a date field, think through the valid and invalid rules for the field.  You might allow 09/09/2002 but not 9/9/2002 or Sep/9/2002.  Work through several examples as follows: Building Regular Expressions That Work

58 Work through several examples

59 Building Regular Expressions that Work 2. Get form and form-handling programs working  Build a sending form the input field  Build the receiving program that accepts the field.  For example, a first cut receiving program: $date = param(‘udate’); if ( $date =~ m/.+/ ) { print ‘Valid date=’, $date; } else { print ‘Invalid date=’, $date; } Any Sequence of characters

60 Building Regular Expressions that Work 3. Start with the most specific term possible.  For example, slashes must always separate two characters (for the month), followed by two more characters (for the day), followed by four characters (for the year). if ( $date =~ m{../../....} ) { Any 2 characters Any 2 characters Any 4 characters

61 Building Regular Expressions that Work 4. Anchor and refine. (Use ^ and $ when possible)  if ( $date =~ m{^\d\d/\d\d/\d\d\d\d$} ) { Starts with 2 digits in middle Ends with 4 digits

62 Building Regular Expressions that Work 5. Get more specific if possible.  The first digit of the month can be only 0, 1, 2 or 3. For example, 05/55/2002 is clearly an illegal date.  Only years from this century are allowed. Because we don’t care about dates like 05/05/1999 or 05/05/3003.

63 Add these rules below if ( $date =~ m{^\d\d/[0-3]\d/2\d\d\d$} ) {  Now the regular expression recognizes input like 09/99/2001 and 05/05/4000 as illegal. Year starts with a “2” Month starts with a “0-3” Building Regular Expressions that Work

64 Tip: Regular Expression Special Variables Perl regexs set several special scalar variables:  $& will be equal to the first matching text  $` will be the text before the match, and  $’ will be the text after the first match. $name='*****Marty'; if ( $name =~ m/\w/ ) { print "got match at=$& "; print "B4=$` after=$'"; } else { print "Not match"; } would output: got match at=M B4=***** after=arty

65 Full Example Program 1. #!/usr/local/bin/perl 2. use CGI ':standard'; 3. print header, start_html('Date Check'); 4. $date=param('udate'); 5. if ($date =~ m{^\d\d/[0-3]\d/2\d\d\d$}){ 6. print 'Valid date=', $date; 7. } else { 8. print 'Invalid date=', $date; 9. } 10. print end_html;

66 Would Output The Following...