CGI Programming

1
CGI Programming
2
Forms

• Forms enable two-way flow of information
• Three important parts
• The FORM tag includes the URL of the scripts
  that processes the data submitted via the form
• The Form Elements like the fields and the menus.
• Submit button Sends the data to the CGI script
  on the server.
• Example
• lt FORM ACTION-http///www.allScripts.com/cgi-bin/s
  cript1.cgi METHOD POST gt
• ltHRgt Please share your comments on the form
  layout
• ltTEXTAREA NAMEcomments ROWS3 COLS65 WRAPgt
  COMMETSlt/TEXTAREAgt
• lt/HRgt
• ltINPUT TYPEsubmit VALUEPRESS TO SUBMITgt
• lt/FORMgt

3

• a) Layout b) script
• data can be gathered by a CGI script and saved
  ltform methodpost actionhttp//www.allscripts
  .com/cgi-bin/script1gtform text lt/formgt
• ltform methodget actionURLofSCRIPTgt form
  text lt/formgt
• single line input (text, checkbox,radio,etc)
• multi line input (text)
• drop-down menus
• HTML Tutorial
• Go to the "NCSA--Beginner's Guide to HTML"
  tutorial located at
• http//www.ncsa.uiuc.edu/General/Internet/WWW/HTML
  PrimerAll.html
• Quick tutorial http//www.jmarshall.com/easy/cgi/
  

4
CGI

• CGI Common Gateway Interface
• A simple protocol to communicate between web
  forms and your program.
• Quick tutorial http//www.jmarshall.com/easy/cgi/
  
• CGI program can be written in any language that
  can read from STDIN, write to STDOUT, and access
  environment variables. e.g., C, Perl, Java,
  Shell.

5
CGI Programming

• 1. Browser requests a URL
• From the Server.
• 2. The requested URL is a script.
• Server executes the script.
• 3. The CGI script may call other programs.
• 4. CGI script passes output back to the server.
• 5. Server passes information back to the browser.
• 6. Browser formats and displays the information
  it receives.

Browser
Server
1
2
5
3
4
CGI-Script
Other Programs
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6

• Typical programming pattern1. Read input data
  from STDIN2. Processing the data3. Write the
  HTML response to STDOUT.
• When a user submit a form, the sequence of
  variables are sent to the server in the following
  format "name1value1name2value2name3value3"
• Standard CGI script input processing1. Split
  the string by "" and "2. Convert all ""
  characters to spaces, and
• You can find input processing funcs in C, Perl,
  etc on the web.

• When the http server receives a submission,
  depending on the submission method of the form,
  the server construct environment variables and
  call the CGI program specified by the form.
• For POST method, the long string can be obtained
  by reading from STDIN. String length is in
  environment variable CONTENT_LENGTH.
• For GET method, the string is in QUERY_STRING
• GET has length limit. POST is more popular.

7

• Sending HTML response back to user just write
  to STDOUTThe first line should be
  Content-Type text/htmlThen write the rest of
  the HTML contents.
• You can send other type of data back to use, such
  as "Content-type image/gif" followed by binary
  gif file data. Not all browsers support all data
  types.
• Sending an existing file to the user as
  response. Write the following to STDOUT
  Location response.html -- followed by a blank
  line.

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Example 1

• A page on the Client Side
• ltA HREFhttp//www.somesite.com/cgi-bin/getDategt
  Display Todays Datelt/Agt

• The script, getDate on the Server Side
• !/bin/sh
• echo Content-type text/plain
• echo
• echo "ltHTMLgtltHEADgt"
• echo "ltTITLEgtgetDate lt/TITLEgt"
• echo "lt/HEADgtltBODYgt"
• today/bin/date
• echo ltPgtTodays Date todaylt/Pgt
• echo "lt/BODYgtlt/HTMLgt"

9
Example 2

• Server side
• cat isOn.cgi
• !/usr/bin/sh
• echo "Content-type text/html"
• echo
• echo "ltHTMLgtltHEADgt"
• echo "ltTITLEgtIs On? lt/TITLEgt"
• echo "lt/HEADgtltBODYgt"
• isonwho grep mjones
• if ! -z "ison"
• then
• echo "ltPgtmjones is logged on.lt/Pgt"
• else
• echo "ltPgtmjones NOT logged onlt/Pgt"
• fi
• echo "lt/BODYgtlt/HTMLgt"

• The Client Side
• ltHTMLgt
• ltHEADERgt ltTITLEgt Is On lt/TITLEgt
• lt/HEADERgt
• ltBODYgt
• ltA HREF"http//www. scu.edu/cgi-bin/isOn.cgi" Is
  Mary Jones Logged Ongt lt/Agt
• lt/BODYgt
• lt/HTMLgt

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A simple perl script to show the input method used

• !/usr/local/bin/perl
• if (ENVREQUEST_METHOD eq GET)
• print ltPgt The request method was ENVREQUEST_M
  ETHOD

• print ltPgtThe data from GET was
• ENVQUERY_STRING
• elsif (
• ENVREQUEST_METHOD eq POST)
• read (STDIN,buffer,ENVCONTENT_LENGTH)

11
Parsing Form Input

• High-lights of parsing a form input.
• The input string should be separated into
  individual fields (separated by a ).
• Field names and values are separated by a .
• Blank spaces encoded as should be converted
  back to spaces.
• Convert special characters encoded as (x
  represents a xx hexadecimal digit) back to their
  character representation.

12
Using C For CGI Programs

• Assume the form consists of the following fields
  and the user has input Mary and chosen Two Years
• ltPgtEnter Your name ltINPUT TYPE"text"
  NAME"theName"gtlt/Pgt
• ltULgt
• ltLIgt ltINPUT TYPE"radio" NAME"years" VALUE"1"
  gt One Year
• ltLIgt ltINPUT TYPE"radio" NAME"years"
  VALUE"5"gt Two Years
• ...
• The string variable, buffer in the program on the
  left side contains the string
• theNameMaryyears5
• the string value in buffer should be parsed to
  separate the fields (and field names and values).

• int length
• char contentLen, buffer
• char method getenv ("REQUEST_METHOD")
• printf("Content-type text/html\n\n")
• printf("lthtmlgt\n")
• if (strcmp(method,"POST") 0)
• printf("ltPgt POST lt/Pgt\n")
• contentLen getenv ("CONTENT_LENGTH")
• if (contentLen ! NULL)
• length atoi(contentLen)
• buffer (char ) malloc (length
  1)
• if (buffer)
• if (fread(buffer,1,length,
  stdin) ! length)
• return
• printf("ltPgt Length d content
  slt/Pgt\n",length,buffer)
• printf("lt/htmlgt\n")

13
PERL

• Perl is an interpreted language for scanning
  files, extracting information from those text
  files, and printing reports based on that
  information.
• Perl is mainly used to handle text files, but can
  be used for binary files (databases), process
  manipulation, network tasks.
• Runs on DOS and UNIX

• Information source http//www.perl.com/perl/
• A Simple Perl program
• !/usr/bin/perl
• This is a comment line
• print Hello\n

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Data Types

• Scalar Values
• days 7
• Arrays
• Indexed by numbers
• _at_days ("Mon", "Tues", "Wed" )
• Hashes
• Indexed by key values
• days ("M" gt "Monday", "T" gt "Tuesday")
• overtime (days"M","5", days"T","10")
• print days"M", "\n"
• print "The number of over time hours on ",
  overtime"Monday"

• _at_daysWorked _at_days
• daysWorked _at_days
• print "Days Worked ", daysWorked, " They are
  "
• print daysWorked0, daysWorked1,
  daysWorked2
• print "\n"

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Data Types

• Examples_at_days (31,28,31,30,31,30,31,31,30,31,30
  ,31) A list with 12 elements.days
  Last index of _at_days 11 for above listdays
  7 shortens or lengthens list _at_days to 8
  elements_at_days3,4,5 (30,31,30)_at_days'a','
  c' same as (days'a',days'c')
• Case is significant--"FOO", "Foo" and "foo"
  are all different variables. If a letter or
  underscore is the first character after the , _at_,
  or , the rest of the name may also contain
  digits and underscores. If this character is a
  digit, the rest must be digits.

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Processing Arrays

• Individual elements in the array can be accessed
  using the index
• Print Today days5
• Print days-1 The last item in the array is
  retrieved
• (day1) _at_days first item
• (day1, day2) _at_days first two items
• noOfDays _at_days length of the array
• Print days prints the last index of the array
• Splitting a scalar into an array
• _at_allnames split (/,/,nameString) splits the
  values in nameString, using the delimiter (comma)
  and loads the values into the array, allNames

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Processing Arrays

• _at_workdays _at_days copies the days array into
  the array, workDays.
• Retrieving the elements from an array
• _at_result _at_workdays 1,2
• _at_myChoices (3,4)
• _at_workDays _at_myChoices
• unshift (_at_workdays, oneMoreDay) adds
  oneMoreDay to the beginning of the array
• push (_at_workdays, oneMoreDay) adds oneMoreDay
  to the end of the array
• _at_totaldays (_at_days,_at_workDays) combines two
  arrays
• _at_days 1,2 _at_twoDays replaces two elements in
  the arrays days.

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Processing Hashes

• A hash (also called associative arrays) contains
  pairs of associated elements the key (first)
  and the value (Second) pairs.
• Example
• days ("M" gt "Monday", "T" gt "Tuesday")
• overtime (daysM,"5", daysT,"10")
• Values in a hash are identified by a key (not by
  an index value).
• Are important in writing CGI scripts using PERL
  since the form parsing routines
• The data gathered from a form is stored in a
  hash.
• The key in each pair is the NAME attribute the
  field name
• The value in the pair is the data that the form
  user has typed in.

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Processing Hashes

• oneday days M Retrieves the value
  associated with the key M.
• _at_holidays days M,T retrieves multiple
  values
• _at_allValues values (days) Retrieves all the
  values
• _at_allKeys keys (days) retrieves all keys
• (key, value) each (days) retrieves each
  pair of key, values
• Exists holidays M returns a true if the
  key exists in the hash

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PERL - Some Examples

• Running a PERL command from the command line.
• perl -e print Hello, World!
• A simple PERL program
• !/usr/bin/perl
• print Enter a line to be displayed on the
  screen
• input ltSTDINgt
• print input
• print Enter first number
• num1 ltSTDINgt
• print Enter second number
• num2 ltSTDINgt
• if (num1 gt num2) print true
• else print false
• using a built-in function
• strLen length(What is the length)
• print strLen

• Creating your own functions
• sub total
• total 0
• foreach num (_at___
• total num
• return total
• Calling the function total
• print total (3,3)

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PERL

• File Processing
• The following program reads two lines of data
  from
• the file, companyData, prints the total stock
  value of
• each company and the total stock value of all
  the
• companies.
• grandTotal 0
• open (STOCKDATA, companyData.txt)
• while (line ltSTOCKDATAgt)
• chomp (line)
• (compName,price,shares) split (/,/,line)
• totVal price shares
• grandTotal totVal
• print Total value of compName holdings
  totval\n
• print The total value of all stock holdings
  grandTotal\n
• close (STOCKDATA)

• companyData.txt
• AlphaBeta,75.0,1032
• EastWest,132.00,500

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Example 3 Calculates the total and average grade
for each student.The file grades contains more
than one score for each student.
!/usr/bin/perl open (GRADES, grades) or die
Cant open grades !\n while (line
ltGRADESgt) (student, grade) split ( ,
line) gradesstudent . grade .
foreach student (sort keys grades) scores
0 total 0 _at_grades split ( ,
gradesstudent) foreach grade (_at_grades)
total grade scores average
total / scores print student grades
student \t Average average\n
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Conditional Statements

• If statement
• (Sky, Space) ("Blue","Colorless")
• if (Sky eq "Colorless" )
• print " Not so\n"
• elsif (sky eq "Blue")
• print "Blue Sky \n"
• print Sky if Sky if statement - a short
  form
• Unless
• unless (destination eq "New York" or
  destination eq Chicago")
• print "Destination destination\n"
• print "No heavy winter clothing may be
  necessary \n"

24
Loops

• last - breaks out of the loop
• next is like continue in C
• count 0
• LINE while (ltSTDINgt) LINE is a label for the
  loop
• last LINE if // Stop on first blank line.
• The continue block is not executed because of
  last
• next LINE if // skip comment lines
• print _
• continue count
• print count, "\n"

25
Loops

• Iterates over a list value and sets the control
  variable to each element of the list.
• Examples
• _at_elements ("Earth", "Sky", "Water", "Space")
• planet ("Mars","Jupiter","Saturn")1
• print planet, "\n"
• foreach element (_at_elements)
• print element
• print "\n"
• days ("M" gt "Monday", "T" gt
  "Tuesday")create a hash
• foreach keyVal (keys days)
• print keyVal
• print "\n" prints T M
• foreach val (values days)
• print val
• print "\n" prints Tuesday Moday