1 / 92

Perl/CGI

Perl/CGI. What We Have Learned and Will Learn. HTML/XHTML: contents CSS: display, layout JavaScript: client side programmability Ajax: based on JavaScript, XML, HTML, CSS Server side programmability CGI: C ommand G ateway I nterface PHP: Open source, strong database support

sebastian-moore
Download Presentation

Perl/CGI

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Perl/CGI

  2. What We Have Learned and Will Learn • HTML/XHTML: contents • CSS: display, layout • JavaScript: client side programmability • Ajax: based on JavaScript, XML, HTML, CSS • Server side programmability • CGI: Command Gateway Interface • PHP: Open source, strong database support • ASP: Microsoft product • …

  3. Command Gateway Interface (CGI) • CGI provides a way by which a web server can obtain data from (or send data to) a database, and other programs, and present that data to viewers via the web • A CGI program can be written in any programming language, but Perl is one of the most popular

  4. Specifics About CGI • A CGI program can be written in any language that allows to be executed on the system: • C/C++ • Fortran • Perl • Python • VB • … • CGI programs are executable • Basically equivalent of letting the world run a program on your system • Security precautions: CGI programs need to reside in a special directory

  5. Perl is A Common Choice • Simple, powerful string manipulation • Flexible pattern matching and substitution • Multi-platform deployment • Abstracted database access • Web server integration • Safe garbage collection • Simple integration with C/C++ for speed

  6. Our First CGI Program – hello.cgi #!/usr/local/bin/perl –w print “Content-type: text/html\r\n\r\n”; print “<html>\n”; print “<head><title>Hello World!</title></head>”; print “<body style=\”text-align:center\”>\n”; print “<h1>Hello World!</h1>\n”; print “</body>”; print “</html>\n”; exit(0); http://www.csupomona.edu/~ftang/www/cgi-bin/hello.cgi http://www.csupomona.edu/cgi-user/ftang/www/cgi-bin/hello.cgi

  7. Anatomy of the Program • First line “#!/usr/local/bin/perl –w” is known as the shebang, which informs the OS of the program that can understand this code (perl, in this case) • The MIME type “Content-type: text/html\r\n\r\n” tells the client’s browser how to interpret the information that follows the declaration • HTML document: the meat • Many possibilities • Return Value • exit (0): normal exit • exit (1): something bad happened

  8. What can Perl Do? • What can Perl do? • print out HTML code • read a template and substitute portion of the template document with some dynamic code • connect to a database and dynamically generate HTML from query results • read in form variables and values from an HTTP request and compute the next HTML page using some process • Have Perl initiate an HTTP request to some other web server, mutate the results and pass them back to the client • … • Basically, if you can code it with Perl, then you can make it web-enabled with not much more effort

  9. What is Perl? • Practical Extraction Report Language • Type “which perl” after we login, this will show us the path of the perl command • In our system, it is under “/usr/local/bin/perl” • You can write perl program and name it “filename.pl” • To run this perl program from terminal • try “perl filename.pl”

  10. Basic Perl • Numeric and String Literals • Variables • Operators • Statements • Control Statements • Functions

  11. Literal • A literal is a value that is hard-coded in your source code • Perl uses four types of literals: • Numbers: the most basic data type • Strings: a string is a series of characters that are handled as one unit • Arrays: an array is a series of numbers and strings handled as a unit; a list • Associative arrays: a list in which every value has an associated lookup item

  12. Numeric Literals and String Literals • Numeric literals • integers such as 4, 043(octal format), 0x23(hex) • float such as .000034 or 3.4E-5 (scientific notation) • String literals (unlike C/C++, no ending NULL character) • Single-quoted ‘hello’ • Can add a line break by adding line break to source code • Double-quoted “hello” • Have special escape sequences \n, \% • Back-quoted `ls –l` • To execute system commands

  13. Literals Continue… • Array literals • () an empty array • (“This”, “is”, “an”, “array”, “of”, “strings”) • Nesting arrays: • ((“Good”, “Morning”), (“Good”, “Afternoon”)) • Use a range of values • print (1..15) will print out numbers from 1 to 15 • print (“A”, “B”, “F”..”H”, “Z”) will print out A, B, F, G, H, Z • Will talk about associative array later

  14. Variables (Three Types) • In Perl, you never have to declare, define, or allocate these data types • Scalar: holds one number or one string at a time • Always begin with a $ • $quantity = 5; $price = 10.3; $name = “blah” • Array: holds a list of values • Always begin with a @ • @emptyArr = ();@numArr=(1..10); @alphabet = (“A”..”Z”); • print @numArr; print $alphabet[25]; • using negative subscripts will print each array element in a reverse order • $numItems = @numArr; # assigns the number of elements in numArr to $numItems

  15. Variable Continue… • Array continue: • How to grab a slice (a part) of an Array • @array = (“1”, “2”, “3”, “4”); • ($first, $third) = @array[0, 2]; • @half = @array[2, 3]; • Associative array: uses any value as an index into an array (like a hashtable) • Always begin with a % • %birthdays = (“Jack”, “Dec 2”, “Joe”, “June 2”, “Jane”, “Feb 13”); • print $birthdays{“Jack”}; • undefined key, return null or blank string

  16. Some Array Functions • push() and pop(): • add or remove an item from the right hand side of an array • push(@mystack, $newvalue); • $off_val = pop(@mystack); • shift() and unshift() • like push() and pop(), but on the left hand side • reverse() • reverse the ordering of list • @a = (1, 2, 3}; @b = reverse(@a);

  17. Some Array Functions • sort() • @x = sort (“small”, “medium”, “large”); • @y = sort(1, 32, 16, 4, 2); # gets (1, 16, 2, 32, 4) sorting is done on the string values of each number (alphabetical) • chop() • removes the last element from an array • chop(“small”, “medium”, “large”);

  18. Associative Array Operators • keys(%arrayname) • lists all the key names in a specified associative array • @names = keys (%birthdays); • values(%arrayname); • returns the values of the specified associative array • @dates = values(%birthdays); • delete • deletes an associated key and value by key reference • delete $birthdays(“Joe”);

  19. Operators • Binary arithmetic operators • +, -, *, /, %, ** • Unary arithmetic operators • +op1, -op1, ++op1, --op1, op1++, op1-- • Logical operators • && (and), || (or), ! (not) • Bitwise operators • & (and), | (or), ^ (exclusive-or), ~ (complement), >> (shift right), << (shift left) • Numeric relational operators • ==, !=, <, <=, >, >= • op1 <=> op2 • returns 1: if op1 is greater than op2 • returns 0: if op1 equals op2 • return –1: if op1 is less than op2

  20. Operators, Continue… • String relational operators • op1 eq op2: returns true if equivalent • op1 ne op2: returns true if not equivalent • op1 lt op2: returns true if op1 is less than op2 • op1 le op2: returns true is op1 is less than or equal to op2 • op1 gt op2: returns true if op1 is greater than op2 • op1 ge op2: returns true if op1 is greater than or equal ot op2 • op1 cmp op2 • returns 1 if op1 is greater than op2 • returns 0 if op1 equals op2 • returns –1 if op1 is less than op2 • Ternary operator • condition-part ? true-part : false-part

  21. Operators, Continue • Range operator .. • @array = (1..10); @array=(“aa”..“af”); • @array = (“ay”..“bf”); • String operators • Concatenation . • $first = “tom”; $second = “jerry”; • $name = $first . “ and ” . $second • Repetition x • $str = $str x 2; # print out the string twice • Assignment operators • var += op1; • …

  22. Operators, Continue • Conversion between numbers and Strings • Scalar variables are converted automatically • $x = “40”; $y = “50”; • $z = $x + $y; # answer 90 • $s = $x.$y; # answer “4050” • chop() • takes a single argument and removes the last character from the string • chop(‘sandy’) would give ‘sand’ • most string inputs in Perl end with a \n. chop() can easily remove it for future processing

  23. Operators, Continue • Assigning an array to scalar variables • @array = (“Tom Jones”, “123 Harley LN”, “Birmingham”, “AR”); • ($name, $street, $town, $state) = @array; • For operators, the order of precedence is always important • parentheses are recommended to explicitly tell Perl how and in which order to evaluate operators

  24. So Far, We Have Learned … • Literals • Variables • Operators • Statement/Statement Block • Function • Reference

  25. Statement and Statement Block • Statements are a complete unit of instruction for the computer to process • A statement block is a group of statements surrounded by curly braces • You can use the my() function to create variables whose scope is limited to the statement block $firstvar = 10; { my($firstvar) = “A”; print $firstvar x 5 . “\n”; } print (“firstvar = $firstvar\n”);

  26. if/unless statement if (expression) { true_statement_1; …. true_statement_n; } if () {…} else {…} if () {…} elsif () {…} else {} unless ($age < 18) {print “Go and Vote\n”;} curly braces are required even if there’s only one statement

  27. Loops • For statement • for (initial_expr; test_expr; increment_expr) {…} • while/until statement • while (expr) {…} # while the expr is true • until (expr) {…} # until the expr is false • foreach statement • foreach $i (@some_list) {…} @a = (1..5); foreach $i (reverse @a) { print $i; }

  28. Jump Keywords • Four keywords • last: jumps out of the current statement block • next: skips the rest of the statement block and continues with the next iteration of the loop • redo: restarts the statement block • goto: jumps to a specified label { print(“What’s your name? ”); $name = <STDIN>; chop($name); # also try chomp() here if (!length($name)) { print(“Msg: Zero length input. Please try again\n”); redo; } print(“Thank you, ” . uc($name) . “\n”); # uc() uppercass }

  29. Function • A function definition in Perl is as follows: sub functionName { } • Using parameters • All parameters to a function are stored in an array called @_. • Perl parameters are called by reference. Changing their values in the function also changes their values in the main program.

  30. A Function Example $areaOfFirstCircle = areaOfCircle(5); print("$areaOfFirstCircle\n"); sub areaOfCircle { $radius = $_[0]; return(3.1415 * ($radius ** 2)); }

  31. Using the Parameter Array (@_) • Perl lets you pass any number of parameters to a function. The function decides which parameters to use and in what order. firstSub(1, 2, 3, 4, 5, 6); firstSub(1..3); firstSub("A".."Z"); sub firstSub { $numParameters = @_ ; print("The number of parameters is $numParameters\n"); } areaOfRectangle(2, 3); areaOfRectangle(5, 6); sub areaOfRectangle { ($height, $width) = @_ ; $area = $height * $width; print("The height is $height. The width is $width. The area is $area.\n\n"); }

  32. @array = (0..5); print("Before func call, array = @array\n"); firstSub(@array); print("After func call, array = @array\n"); sub firstSub { $_[0] = "A"; $_[1] = "B"; } @array = (0..5); print("Before func call, array = @array\n"); firstSub(@array); print("After func call, array = @array\n"); sub firstSub{ ($firstVar, $secondVar) = @_ ; $firstVar = "A"; $secondVar = "B"; } Passing Parameters by Reference • Perl parameters are called by reference, changing their values in the function also changes their values in the main program.

  33. Scope of Variables • Scope refers to the visibility of variables. • Normally, every variable has a global scope. • Two Perl’s built-in functions can create variables of limited scope. • my() : visible to the current function only • local() : visible to the current function and any functions that are called by the current function • using my() enforces good programming practices and reduces headaches

  34. Using a List as a Function Parameter • You can pass many scalar values as you want to a function, but only on an array. If you try to pass more than one array, the array elements become joined together and passed as one array to the function. • To pass both scalar and array, put scalar type first, and then array to distinguish them • Nested functions

  35. String Functions • chomp (string or array): remove the trailing newline if it exists from a string or each element of an array • chop(string or array): removes the last character from a string or from every element in an array. The last character chopped is returned • index(string, substring, position): returns the position of the first occurrence of substring in string at or after position • rindex(string, substring, position) : returns the position of the last occurrence of substring in string at or after position • join(string, array): returns a string that consists of all the elements of array joined together by string

  36. More String Functions • split(pattern, string, limit) • breaks up a string using pattern as the delimiter. • The limit parameter indicates how many parts to create from string • substr(string, offset, length) • returns a portion of a string as determined by the offset and length parameters. • lc(string), uc(string): lowercase; uppercase • lcfirst(string), ucfirst(string) • length(string) • Note as a general rule, if Perl sees a number where it expects a string, the number is automatically converted to a string • Note that some of the string functions use the special variable $_ as the default string to work with

  37. Array Functions • defined(variable) • returns true if the variable has a real value and false if the variable has not yet been assigned a value • delete(key) • removes the key-value pair from the given associative array, e.g., delete($arr{“orange”}) • exists(key) • each(assoc_arr) • returns a list that contains key-value pairs from the associative array, so that it’s easy to iterate through • keys(assoc_arr) • returns a list of keys • values(assoc_arr) • returns a list of values

  38. More Array Functions • pop, push, reverse, sort • shift/unshift: • shift(array): returns the first value of an array and reduces the size by one • unshift(arr1, arr2): adds the elements of arr2 to the front of arr1

  39. Reference • A reference is a scalar value that points to a memory location that holds some type of data • All of your variables and functions are located at some memory location • References are used to hold the memory addresses • When a reference is dereferenced, you can retrieve the information referred to by the reference

  40. Common Reference Types • $refScalar = \$scalar; • ${$refScalar} is a scalar value • $refArray = \@array; • @{$refArray} is an array value • $refHash = \%hash; • %{$refHash} is a hash value • $refRef = \$refScalar; • ${${$refRef}} is a scalar value • $refglob = \*file; • $refFunction = \&function; • &{$refFunction} is a function location

  41. Passing Parameters to Functions @array1 = (1..5); @array2 = ("A".."E"); firstSub( \@array1, \@array2); sub firstSub { my($ref_firstArray, $ref_secondArray) = @_; print("The first array is @{$ref_firstArray}.\n"); print("The second array is @{$ref_secondArray}.\n"); } This program displays: The first array is 1 2 3 4 5. The second array is A B C D E.

  42. The ref() Function • Using references to pass arrays into a function is easy • However, what if you pass a scalar reference to a function instead of an array reference? firstSub( 10, ("A".."E") ); sub firstSub { my($ref_firstArray, $ref_secondArray) = @_ ; print("The first array is @{$ref_firstArray}.\n"); print("The second array is @{$ref_secondArray}.\n"); } This program displays: Not an ARRAY reference at 08lst01.pl line 9.

  43. The ref() Function (Con’t.) • ref() function can help you check the reference type before dereferencing a reference • ref(10); # return value is undefined • ref(\10); # return value is “SCALAR” • ref(\(1..10)); # return value is “ARRAY” • ref(\{1 => “Joe”}); # return value is “HASH” • ref(\&firstSub); # return value is “CODE” • ref(\\10); # return value is “REF” firstSub( 10, ("A".."E") ); sub firstSub { my($ref_firstArray, $ref_secondArray) = @_ ; print("The first array is @{$ref_firstArray}.\n") if (ref($ref_firstArray) eq "ARRAY"); print("The second array is @{$ref_secondArray}.\n" if (ref($ref_secondArray) eq "ARRAY"); }

  44. Creating a Data Record • Associate arrays (hashes) are extremely useful to store information that facilitates easy retrieval %recordOne = ( "Name" => "Jane Hathaway", "Address" => "123 Anylane Rd.", "Town" => "AnyTown", "State" => "AnyState", "Zip" => "12345-1234“ ); %recordTwo = ( "Name" => "Kevin Hughes", "Address" => "123 Allways Dr.", "Town" => "AnyTown", "State" => "AnyState", "Zip" => "12345-1234" ); @database = ( \%recordOne, \%recordTwo ); print( %{$database[0]}->{"Address"} . "\n");

  45. More on Perl Programming • Files (Input/Output) • Regular Expression • Special Variables

  46. Using Files • Four basic operations: open, read, write, close • Three standard file handles: • STDIN: reads program input from the computer’s keyboard • STDOUT: displays program output to the computer’s monitor • STDERR: displays program errors, equivalent to STDOUT most of the time

  47. Read From STDIN • Read a line of input from the standard input, STDIN • This will continue until you press Ctrl+D on Unix systems while (<STDIN>) { # diamond operators, default $_ print(); } # the following program acts the same as the above while ($tmpline = <STDIN>) { print ($tmpline); }

  48. Using the Diamond Operators • If no file handle is used with the <>, Perl will examine the @ARGV special variable. If @ARGV has no elements, then the diamond operator will read from STDIN while (<>) { print(); } >perl file2.pl str1.pl str2.pl Perl will create the @ARGV array from the command line. Each file name on the command line – after the program will be added to the @ARGV array as an element. Normally, using <> to iterate over a list of filenames is handy.

  49. File Functions • Open a file to read: $INPUT_FILE = "fixed.dat"; open(INPUT_FILE); @array = <INPUT_FILE>; close(INPUT_FILE); foreach (@array) { print(); } A file can be opened in many different ways: to read, write, append, etc. • Or: • open(FILE, “<fixed.dat”); • @array = <FILE>; • close(FILE); • foreach (@array) { • print(); • } • Or • open (FILE, “fixed.dat”) • || die “cannot open file”; • while (<FILE>) { • print $_; • } • close (FILE);

  50. Examples • Call the open() function to open “message.log” file for writing with LOGFILE as the file handle if (open(LOGFILE, ">message.log")) { print LOGFILE ("This is message number 1.\n"); print LOGFILE ("This is message number 2.\n"); close(LOGFILE); } • Call the open() function to append to “message.log” if (open(LOGFILE, ">>message.log")) { print LOGFILE ("This is message number 3.\n"); close(LOGFILE); }

More Related