A Guide to Unix Using Linux Fourth Edition

1. A Guide to Unix Using Linux Fourth Edition Chapter 9 Perl and CGI Programming

2. Objectives • Understand the basics of the Perl language • Identify and use data types in Perl scripts • Understand differences between the Awk program and Perl programming • Access disk files in Perl A Guide to Unix Using Linux, Fourth Edition

3. Objectives (continued) • Use Perl to sort information • Set up a simple HTML Web page • Understand how Perl and CGI are used for creating Web pages A Guide to Unix Using Linux, Fourth Edition

4. Introduction to Perl • Perl: Practical Extraction and Report Language • Free script language • Runs on many operating systems • Examples: UNIX, Linux, Windows, Mac OS X • Manipulates text, displays output, handles mathematical processes, and works with files • Generating reports • Used for Web programming • Released by Larry Wall in 1987 • Interpreted language • Interpreter: /usr/bin/perl A Guide to Unix Using Linux, Fourth Edition

5. Introduction to Perl (continued) #!/usr/bin/perl # Program name: example1.pl print("This is a simple\n"); print("Perl program.\n"); A Guide to Unix Using Linux, Fourth Edition

6. Introduction to Perl (continued) • The following script uses a variable: • Output: #!/usr/bin/perl # Program name: example2.pl $name = "Charlie"; print ("Greetings $name\n"); [ellen@localhost ~]$ ./example2.pl Greetings Charlie A Guide to Unix Using Linux, Fourth Edition

7. Introduction to Perl (continued) #!/usr/bin/perl # Program name: example3.pl print ("Enter a number: "); $number = <STDIN>; print ("You entered $number\n"); A Guide to Unix Using Linux, Fourth Edition

8. Introduction to Perl (continued) #!/usr/bin/perl # Program name: example4.pl print ("Enter a number: "); $number = <STDIN>; if ($number == 10) { print ("That is the number I was thinking of.\n"); } else { print ("You entered $number\n"); } A Guide to Unix Using Linux, Fourth Edition

9. Introduction to Perl (continued) A Guide to Unix Using Linux, Fourth Edition

10. Introduction to Perl (continued) A Guide to Unix Using Linux, Fourth Edition

11. Introduction to Perl (continued) • Perl offers the if-else statement: • Output: #!/usr/bin/perl # Program name: example5.pl $my_name = "Ellen"; $your_name = "Charlie"; if ($my_name eq $your_name) { print ("Your name is the same as mine.\n"); } else { print ("Hello. My name is $my_name\n"); } [ellen@localhost ~]$ ./example5.pl Hello. My name is Ellen A Guide to Unix Using Linux, Fourth Edition

12. Introduction to Perl (continued) • Perl provides standard arithmetic operators: • Output: #!/usr/bin/perl # Program name: example6.pl $num1 = 10; $num2 = 50; $num3 = 12; $average = ($num1 + $num2 + $num3) / 3; print ("The average is $average\n"); [ellen@localhost ~]$ ./example6.pl The average is 24 A Guide to Unix Using Linux, Fourth Edition

13. Identifying Data Types • In Perl, data can be represented in a variety of ways • Variables and constants • Scalars • Numbers • Strings • Arrays • Hashes A Guide to Unix Using Linux, Fourth Edition

14. Variables and Constants • Variables: symbolic names that represent values stored in memory • Examples: • $x might hold the value 100 • $name might hold the sequence of characters Charlie • Value can change while program runs • Constants do not change value as the program runs • Written into the program code itself • Example: $num = 127.89 A Guide to Unix Using Linux, Fourth Edition

15. Scalars • Scalar: simple variable that holds a number or string • Name begins with a $ • Examples: • $x = 12; • $name = "Jill"; • $pay = 12456.89; A Guide to Unix Using Linux, Fourth Edition

16. Numbers • Numbers are stored inside the computer as: • Signed integers (e.g., 14321) • Double-precision, floating-point values (e.g., 56.85) • Numeric literals are integers or floating-point values • Perl uses underscore (_) to improve legibility: • Example: 5_456_678_901 • Only works within literal numbers specified in a program • 0x used to express hexadecimal constants A Guide to Unix Using Linux, Fourth Edition

17. Strings • Strings are sequences of any types of characters • Delimited by ‘’ or “” • Single-quoted strings are not subject to interpolation • Except for \' and \\ • In double-quoted strings, variables are interpolated • Backslash (\) used to ensure variable or control character is not interpolated A Guide to Unix Using Linux, Fourth Edition

18. Strings (continued) A Guide to Unix Using Linux, Fourth Edition

19. #!/usr/bin/perl # Program name: example7.pl print ("\\words\\separated\\by\\slashes\n"); print ("This is a \"quote\"\n"); print ("\Uupper case\n"); print ("\LLOWER CASE\n"); A Guide to Unix Using Linux, Fourth Edition

20. Arrays • Arrays are variables that store an ordered list of scalar values • Elements are accessed with numeric subscripts • Starting at zero • Elements are usually of the same data type • An “at” sign (@) precedes the name of an array when assigning it values • $ character used when processing the individual elements A Guide to Unix Using Linux, Fourth Edition

21. #!/usr/bin/perl # Program name: example8.pl @pets = ("dog", "cat", "parrot", "hamster" ); print ("My pets are:\n"); print ("$pets[0]\n"); print ("$pets[1]\n"); print ("$pets[2]\n"); print ("$pets[3]\n"); A Guide to Unix Using Linux, Fourth Edition

22. Hashes • Hash: variable that represents a set of key/value pairs • Hash variables are preceded by % when they are assigned values %animals = (’Tigers’, 10, ’Lions’, 20, ’Bears’, 30); %animals = (Tigers ==> 10, Lions ==> 20, Bears ==> 30); • To refer to an element, use $ before the variable name followed by the key in {} $animals{’Bears’} A Guide to Unix Using Linux, Fourth Edition

23. Hashes (continued) • Example: • Output: #!/usr/bin/perl # Program name: example9.pl %animals = (’Tigers’, 10, ’Lions’, 20, ’Bears’, 30); print ("The animal values are:\n"); print ("$animals{’Tigers’}\n"); print ("$animals{’Lions’}\n"); print ("$animals{’Bears’}\n"); [ellen@localhost ~]$ ./example9.pl The animal values are: 10 20 30 A Guide to Unix Using Linux, Fourth Edition

24. Perl Versus the Awk Program • Unlike Perl, Awk does not require programmer to explicitly set up looping structures • Uses fewer lines of code to resolve pattern-matching extractions than Perl • Similarities: • Perl and Awk use # to specify a comment line • Pattern-matching code is the same in both programs • Both are portable across many UNIX/Linux systems A Guide to Unix Using Linux, Fourth Edition

25. #!/usr/bin/awk -f # Program name: awkcom.a # Purpose: Count the comment lines in a file. # Enter the file name on the command line. END { print "The file has ", line_count, " comment lines." } /^#/ && !/^#!/ { ++line_count } # This occurs for every line. A Guide to Unix Using Linux, Fourth Edition

26. #!/usr/bin/perl # Program name: perlcom.pl # Purpose: Count the source file’s comment lines # ============================================== $filein = $ARGV[0]; while (<>) { if (/^#/ && !/^#!/) { ++$line_count } } print ("File \"$filein\" has $line_count comment lines. \n"); <> is the diamond operator A Guide to Unix Using Linux, Fourth Edition

27. How Perl Accesses Disk Files • Perl uses filehandles to reference files • Filehandle: name for an I/O connection between Perl program and OS • Used to open, read, write, and close the file • Convention: use all uppercase letters for filehandles • Must issue an open before you can access file • Exception: when file name passed through ARGV[0] • Three standard filehandles in Perl: • STDIN, STDOUT, and STDERR A Guide to Unix Using Linux, Fourth Edition

28. #!/usr/bin/perl # Program name: perlread1.pl # Purpose: Display records in a file and count lines $filein = $ARGV[0]; while (<>) { print "$_"; ++$line_count; } print ("File \"$filein\" has $line_count lines. \n"); #!/usr/bin/perl # Program name: perlread2.pl # Purpose: Open disk file. Read and display the records # in the file. Count the number of records in # the file. open (FILEIN, "students") || warn "Could not open students file\n"; while (<FILEIN>) { print "$_"; ++$line_count; } print ("File \"students\" has $line_count lines. \n"); close (FILEIN); A Guide to Unix Using Linux, Fourth Edition

29. Using Perl to Sort • Perl provides a powerful and flexible sort operator • Can sort string or numeric data • In ascending or descending order • Allows advanced sorting • Define your own sorting routine A Guide to Unix Using Linux, Fourth Edition

30. Using Perl to Sort Alphanumeric Fields • Perl can be used to sort information • Example: #!/usr/bin/perl # Program name: perlsort1.pl # Purpose: Sort a list of names contained inside an array # Syntax: perlsort1.pl <Enter> #======================================================== @somelist = ("Oranges", "Apples", "Tangerines", "Pears", "Bananas", "Pineapples"); @sortedlist = sort @somelist; print "@sortedlist"; print"\n"; A Guide to Unix Using Linux, Fourth Edition

31. Using Perl to Sort Alphanumeric Fields (continued) • Another example: #!/usr/bin/perl # Program name: perlsort2.pl # Purpose: Sorts a text file alphabetically. File name is # entered on the command line. # Syntax: perlsort2.pl file name <Enter> #======================================================== $x = 0; while (<>) { $somelist[$x] = $_; $x++; } A Guide to Unix Using Linux, Fourth Edition

32. Using Perl to Sort Numeric Fields • For numeric fields, you can define a subroutine with the comparison conditions sub numbers { if ($a < $b) { -1; } elsif ($a == $b) { 0; } else { +1; } } $sortednumbers = sort numbers 101, 87, 34, 12, 1, 76; A Guide to Unix Using Linux, Fourth Edition

33. Using Perl to Sort Numeric Fields (continued) • Perl has a special operator for numeric sorts: <=> • Spaceship operator • The inline sort blockis even more compact sub numbers { $a <=> $b; } $sortednumbers = sort numbers 101, 87, 34, 12, 1, 76; @sortednumbers = sort { $a <=> $b; } @numberlist; A Guide to Unix Using Linux, Fourth Edition

34. #!/usr/bin/perl # Program name: perlsort3.pl # Purpose: Sorts numerically using a subroutine. File name # is entered on the command line. # Syntax: perlsort3.pl file name <Enter> #======================================================== $x = 0; while (<>) { $somelist[$x] = $_; $x++; } @sortedlist = sort numbers @somelist; print @sortedlist; sub numbers { if ($a < $b) { -1; } elsif ($a == $b) { 0; } else { +1; } } A Guide to Unix Using Linux, Fourth Edition

35. Using Perl to Sort Numeric Fields (continued) A Guide to Unix Using Linux, Fourth Edition

36. Using Perl to Sort Numeric Fields (continued) #!/usr/bin/perl # Program name: perlsort4.pl # Purpose: Sort numerically using the spaceship operator # (<=>) # syntax: perlsort4.pl file name <Enter> #======================================================== $x = 0; while (<>) { $somelist[$x] = $_; $x++; } @sortedlist = sort numbers @somelist; print @sortedlist; sub numbers { $a <=> $b; } A Guide to Unix Using Linux, Fourth Edition

37. Setting Up a Web Page • Create a Web page using HTML • HTML: Hypertext Markup Language • Format for creating documents with embedded tags • Tags give the document special properties and let you place hyperlinks in a document • Publish a Web page on a Web server • Experiment with and test HTML documents using your system’s loopback address • 127.0.0.1 or localhost A Guide to Unix Using Linux, Fourth Edition

38. Creating a Simple Web Page • To create Web pages: • Use a visual HTML editor • Examples: Adobe Dreamweaver, Microsoft Expression Web • “What you see is what you get” • Use a text editor • Examples: vi, Emacs • Just type text and the desired embedded tags A Guide to Unix Using Linux, Fourth Edition

39. <HTML> <HEAD><TITLE>My Simple Web Page</TITLE></HEAD> <BODY> <H1>Just a Simple Web Page</H1> This is a Web page with no frills! </BODY> </HTML> A Guide to Unix Using Linux, Fourth Edition

40. Creating a Simple Web Page (continued) <HTML> <HEAD><TITLE>UNIX/Linux Programming Tools</TITLE></HEAD> <BODY> <H1><CENTER>My UNIX/Linux Programming Tools</CENTER></H1> <H2>Languages</H2> <P>Perl</P> <P>Shell Scripts</P> <P>C and C++</P> <H2>Editors</H2> <P>vi</P> <P>Emacs</P> <H2>Other Tools</H2> <P>awk</P> <P>sed</P> </BODY> </HTML> A Guide to Unix Using Linux, Fourth Edition

41. CGI Overview • Perl is the most commonly used language for Common Gateway Interface (CGI) programming • CGI is a protocol governing how browsers and servers communicate • Exchanging and processing a form containing information typically involves: • Using CGI for communication between the client’s Web browser and the Web server • A program that can be executed • Often a Perl script or a program written in C • Often stored in cgi-bin subdirectory on Web server A Guide to Unix Using Linux, Fourth Edition

42. CGI Overview (continued) • Programs in cgi-bin are set up to have executable permissions • Also typically have r permissions so client can view associated Web page • To allow HTML document to accept input, precede input area with a description: Total Cost? <INPUT TYPE=text NAME=cost SIZE=10> • Some links of interest: • www.scriptarchive.com • www.perl.com • www.perlaccess.com A Guide to Unix Using Linux, Fourth Edition

43. Summary • Perl is a scripting language • Data types: variables, constants, scalars, strings, arrays, and hashes • Perl and Awk are both powerful processing languages that function in different ways • Perl uses filehandles for the I/O connection between a file and Perl • In Perl, use <=> operator for numeric sorts • HTML is used to format text in a Web page • CGI is a protocol that governs how browsers and servers communicate A Guide to Unix Using Linux, Fourth Edition

44. Command Summary A Guide to Unix Using Linux, Fourth Edition