Perl Practical Extraction and Report Language Perl: Developed by Larry Wall in the late 1980s. Builds on... sh awk sed c Perl is a fully general programming language, but it’s particularly well-adapted to processing “text”. CSE 341 -- S. Tanimoto Perl Introduction
CSE 341 -- S. Tanimoto Perl Introduction Scripting Languages Scripting in Drama: programming the sequence of actor’s actions and utterances. A play is represented by a script. Scripting in software systems: programming a sequence of operations to be performed by a software system. Scripting operations are typically higher-level operations than machine instructions, typically application-oriented. Examples: Gnu Emacs is scripted with elisp. The GIMP (Gnu Image Manipulation Program) is scripted with a dialect of Scheme. Shell-level scripting language: Glue that ties together programs written in other languages. CSE 341 -- S. Tanimoto Perl Introduction
Is Scripting a Paradigm? No, not like functional programming or object-oriented programming. Scripting does not seem to require a different model for how computation works. Yet there are noticeable patterns that arise in scripts for particular types of applications. In CGI scripting for the web, many scripts begin by collecting input data, using it to access a database, and then they output a web page. But yes, we can view scripting as a paradigm, in the general sense of the word as a model or example of a way of programming. CSE 341 -- S. Tanimoto Perl Introduction
CSE 341 -- S. Tanimoto Perl Introduction Perl and the Web One-pass compilation means Perl programs can be efficiently compiled on demand. Perl makes it easy to process text (and generate HTML!). With contributed modules in the CPAN library, Perl has become a defacto standard for CGI programming on the Web, esp. on Unix servers. CSE 341 -- S. Tanimoto Perl Introduction
CSE 341 -- S. Tanimoto Perl Introduction Perl vs Java Server vs Client... Input info may be too sensitive to send over the net to an applet. Applet downloading and startup cause high latency. No special browser plugins are needed, since Perl doesn’t run in the browser. CSE 341 -- S. Tanimoto Perl Introduction
Perl has a “Little Language” philosophy Perl programs traditionally have been small. Perl itself, though not small, is to some extent a successor of awk and sed. Small numbers of variables means less concern about name conflicts... declarations not required. Perl grows out of a systems-programming context. Conciseness was valued over transparency. The meanings of language features are often dependent on context (e.g., list context vs scalar context). One system may consist of many Perl scripts. CSE 341 -- S. Tanimoto Perl Introduction
Comments on the Book by Sebesta A Little Book on Perl, by Robert W. Sebesta is a recent book (2000). It covers Perl 5.005. (Perl 5.8 has since come out, but Sebesta's book is generally consistent with it.) The book is clearly written and covers the right stuff. Sebesta is the author of a popular text on programming languages. CSE 341 -- S. Tanimoto Perl Introduction
CSE 341 -- S. Tanimoto Perl Introduction Running a Perl Program Perl was originally intended for use under Unix, but has since been ported to the PC. We’ll assume a Unix (Linux) environment here. #!/usr/bin/perl print("Out of the oyster!\n"); # comment Make sure the file is executable: chmod +x howdy.pl Run the program from the command line: ./howdy.pl CSE 341 -- S. Tanimoto Perl Introduction
A Perl Script for the Web #!/usr/bin/perl print "Content-type: text/html\n\n"; $now = localtime(); print "<html><body>"; print "<h2>The time is $now\n"; print " </h2></body></html>"; CSE 341 -- S. Tanimoto Perl Introduction
CSE 341 -- S. Tanimoto Perl Introduction Online help perldoc perl (overview) perldoc perlfaq (freq. asked questions) perldoc perldata (data structures) perldoc perlsyn (syntax) perldoc perlop (operators and precedence) perldoc perlre (regular expressions) perldoc perlrun (execution and options) perldoc -f split (info on a function) CSE 341 -- S. Tanimoto Perl Introduction
The Fundamental Data Types $n = 25; # a numeric scalar $str = "Here is a string"; print('The value of $n is ' . $n); # Note strings with ' ' do not have # variable "interpolation" performed # But strings with " " DO have it. print("The value is $n."); CSE 341 -- S. Tanimoto Perl Introduction
CSE 341 -- S. Tanimoto Perl Introduction String Operations "string1" . "string2" # concatenation Can also be done using interpolation: $str1 = "abc"; $str2 = "def"; $newstr = "$str1$str2"; CSE 341 -- S. Tanimoto Perl Introduction
Support for processing text: Immediate, embedded (“Here”) Documents print << "END-OF-PRINT"; Hello there. This is a two-line immediate text doc. END-OF-PRINT CSE 341 -- S. Tanimoto Perl Introduction
Choice of Interpolating or Not $dollars = 64000; print <<”EOT”; The $dollars question. Are $dollars printed out here? EOT CSE 341 -- S. Tanimoto Perl Introduction
Choice of Interpolating or Not $dollars = 64000; print <<’EOT’; The $64000 question. Are $dollars printed out here? EOT CSE 341 -- S. Tanimoto Perl Introduction
CSE 341 -- S. Tanimoto Perl Introduction Interpolation -- Not The $64000 question. Are $dollars printed out here? CSE 341 -- S. Tanimoto Perl Introduction
CSE 341 -- S. Tanimoto Perl Introduction Arrays In Perl, arrays are data structures that hold lists. @trees = ("Oak", "Maple", "Madrona"); @moretrees = qw(pine alter hemlock); @ages = (75, 50.5, "twenty"); $mytree = $trees[1]; # "Maple" CSE 341 -- S. Tanimoto Perl Introduction
Hashes (Associative Arrays) $foodtype{"Spaghetti"} = "Italian"; $thetype = $foodtype{"Spaghetti"}; foreach $food (keys %foodtype) { $thetype = $foodtype{$food}; print "Food $food is $thetype\n"; } CSE 341 -- S. Tanimoto Perl Introduction
Quick Example of CGI Processing: The HTML Form <html><body> <form method=post action="http://www.domain.edu/do-something.pl"> Type your user name: <input type=text name=username size=20> <input type=submit value="Click here"> </form> </body></html> CSE 341 -- S. Tanimoto Perl Introduction
CGI Processing: The Perl Script #!/usr/bin/perl use CGI qw/:standard/; $theName = param("username"); print "Content-type: text/html\n\n"; print " <html><body><h2>"; print " Your user name is $theName"; print "</h2></body></html>"; CSE 341 -- S. Tanimoto Perl Introduction