Introduction to Programming the WWW I

1
Introduction to Programming the WWW I

• CMSC 10100-1
• Winter 2004
• Lecture 12

2
Todays Topics

• CGI module (contd)
• Matching patterns
• Regular expressions

3
Midterm Results

• Total points of the paper 50
• Highest grade 47.5
• Avg. grade 42.6
• 10 submitted papers
• 9 papers with grade gt 40

4
Review Using CGI.pm to generate HTML

• The CGI.pm module provides several functions
  that can be used to concisely output HTML tags
• For example,
• mypageIt is a New Day
• print ltHTMLgtltHEADgtltTITLEgt mypage
  lt/TITLEgtlt/HEADgtltBODYgt
• can also be written as
• mypageIt is a New Day
• print start_html(mypage)

5
Review Three Basic CGI.pm Modules

• start_html
• creates starting HTML tags
• Header
• creates the MIME Content-type line
• end_html
• creates ending HTML tags

1.     !/usr/local/bin/perl 2.     use CGI
standard 3.     print header 4.     print
start_html 5.     print 'ltFONT size4
color"blue"gt' 6.     print 'Welcome
ltIgthumanslt/Igt to my sitelt/FONTgt' 7. print
end_html
6
Review 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

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Review Some Single Argument Functions
8
Review Some Positional Functions
9
Review Some name/value functions
 
10
Review How Web Applications Work with CGI
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Review HTLM Forms

• HTML Forms are used to select different kinds of
  user input, defined with ltformgt tag
• Form contains form elements to allow the user to
  enter information
• text fields
• textarea fields
• drop-down menus
• radio buttons
• checkboxes, etc

12
Review ltformgt Tag Attributes

• action attribute
• Gives the URL of the program(CGI) to receive and
  process the forms data
• method attribute
• Sets the HTTP method by which the browser sends
  the form data to the program, value can be GET or
  POST
• Avoid GET method in favor of POST for security
  reasons

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Review ltinputgt Tag

• To define any one of a number of common form
  controls
• Text fields (including password, hidden fields)
• multiple-choice lists
• Clickable images
• Submission buttons
• Only type and name attribute required
• No ending tag (no lt/inputgt)

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Review Text Fields

• single line of text
• ltinput typetext nameXXXgt
• Set type to password to mask text like a password
• Set type to hidden to create a hidden field
• size and maxlength attributes
• value attributes to give default text

15
Review Multi-line Text Area

• The lttextareagt tag
• Attributes
• cols
• rows
• wrap
• Values Off,virtual(default),physical

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Review Check Boxes

• Check boxes for check all that apply questions
• ltinput typecheckbox nameXXX valueXXXgt
• Make sure name identical among a group of
  checkboxes
• checked attribute
• When form is submitted, names and values of those
  checked boxes are sent

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Review Radio Buttons

• Similar as checkboxes, but only one in the group
  may be selected
• ltinput typeradio nameXXX valueXXXgt

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Review Multiple Choice Elements

• The ltselectgt tag creates either pull-down menus
  or scrolling lists
• The ltoptiongt tag defines each item within a
  ltselectgt tag
• ltselectgt tag attributes
• size attribute
• Number of rows visible at the same time
• multiple attribute
• If set, allow multiple selections
• name attribute

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Review Action Buttons

• What are they?
• Submit buttons
• ltinput typesubmit nameXXX valueXXXgt
• Reset buttons
• ltinput typereset nameXXX valueXXXgt
• Regular buttons
• ltinput typebutton nameXXX valueXXXgt
• image buttons (will send form content as submit
  button)
• ltinput typeimage nameXXX srcXXXgt
• File buttons (need to deal with enctyple
  attribute)
• ltinput typefile nameXXX accepttext/gt

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Using CGI.pm with HTML forms
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Using CGI.pm with HTML forms (contd)

Perl CGI Reference
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A CGI Form Example
http//people.cs.uchicago.edu/hai/hw4/cgiform1.cg
i
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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()

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Receiving HTML Form Arguments
http//people.cs.uchicago.edu/hai/hw4/cgiform1.cg
i
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Sending Arguments

• You can send arguments to your CGI program
  directly from the URL address of a browser

http//people.cs.uchicago.edu/hai/hw4/cgiform1_ch
ecker.cgi?colorred
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Sending Multiple Arguments
http//people.cs.uchicago.edu/hai/hw4/cgiform1_ch
ecker.cgi?colorredsecretnothing
Precede first argument with ?
Precede next argument with
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Debug CGI Program in Command Line

• To start and send an argument to the password
  program can execute the following
• perl cgiform1_checker.cgi colorred
• Enclose blank spaces or multiple arguments in
  quotation marks
• perl cgiform1_checker.cgi colorrose red
• perl cgiform1_checker.cgi 'colorredsecretnone'

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Check CGI VariablesValues

• 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

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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.

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Combining Program Files
http//people.cs.uchicago.edu/hai/hw4/cgiform2.cg
i
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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.

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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.

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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.

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Possible Values of name
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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 mltDavegt )
• The reverse binding operator test if pattern is
  NOT found
• if ( color ! m/blue/ )

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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

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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 Namename
• The output of this code would be
• NameTom turtle

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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 Namename
• The output of this code would be
• Name Tom TurTle

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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 "namename"
• Would output the following
• NameSMOKEY

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A Full Pattern Matching Example

• 1. !/usr/local/bin/perl
• 2. use CGI 'standard'
• 3. print header, start_html('Command Search')
• 4. _at_PartNums( 'XX1234', 'XX1892', 'XX9510')
• 5. comparam('command')
• 6. prodparam('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 ( _at_PartNums )
• 11. if ( item eq prod )
• 12. print "VALIDATED commandcom
  prodnumprod"
• 13. found 1
• 14.
• 15.
• 16. if ( found ! 1 )
• 17. print br,"Sorry Prod Numprod
  NOT FOUND"
• 18.
• 19. else

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Would Output The Following ...
42
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.

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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.

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Example Alternation Operator
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Parenthesis For Groupings

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

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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

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Special Character Classes
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Special Character Classes - II
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Special Character Classes - III
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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.

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Selected Perl Character Quantifiers I
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Selected Perl Character Quantifiers II
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Selected Perl Character Quantifiers III
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Building Regular Expressions That Work

• Regular expressions are very powerfulbut 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).

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Building Regular Expressions That Work

• 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

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Work through several examples
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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
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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 4 characters
Any 2 characters
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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
2 digits in middle
Ends with 4 digits
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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 dont care about dates like 05/05/1999 or
  05/05/3003.

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Building Regular Expressions that Work

• 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.

Month starts with a 0-3
Year starts with a 2
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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 atM B4 afterarty

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Full Example Program

• 1. !/usr/local/bin/perl
• 2. use CGI 'standard'
• 3. print header, start_html('Date Check')
• 4. dateparam('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

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Would Output The Following ...