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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 S. Tanimoto Perl Introduction
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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 S. Tanimoto Perl Introduction
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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 S. Tanimoto Perl Introduction
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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 S. Tanimoto Perl Introduction
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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 S. Tanimoto Perl Introduction
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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 S. Tanimoto Perl Introduction
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Comments on the Book by Sebesta
A Little Book on Perl, by Robert W. Sebesta is a recent book (2000). It covers Perl (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 S. Tanimoto Perl Introduction
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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 S. Tanimoto Perl Introduction
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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 S. Tanimoto Perl Introduction
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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 S. Tanimoto Perl Introduction
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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 S. Tanimoto Perl Introduction
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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 S. Tanimoto Perl Introduction
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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 S. Tanimoto Perl Introduction
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Choice of Interpolating or Not
$dollars = 64000; print <<”EOT”; The $dollars question. Are $dollars printed out here? EOT CSE S. Tanimoto Perl Introduction
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Choice of Interpolating or Not
$dollars = 64000; print <<’EOT’; The $64000 question. Are $dollars printed out here? EOT CSE S. Tanimoto Perl Introduction
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CSE 341 -- S. Tanimoto Perl Introduction
Interpolation -- Not The $64000 question. Are $dollars printed out here? CSE S. Tanimoto Perl Introduction
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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 S. Tanimoto Perl Introduction
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Hashes (Associative Arrays)
$foodtype{"Spaghetti"} = "Italian"; $thetype = $foodtype{"Spaghetti"}; foreach $food (keys %foodtype) { $thetype = $foodtype{$food}; print "Food $food is $thetype\n"; } CSE S. Tanimoto Perl Introduction
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Quick Example of CGI Processing: The HTML Form
<html><body> <form method=post action=" Type your user name: <input type=text name=username size=20> <input type=submit value="Click here"> </form> </body></html> CSE S. Tanimoto Perl Introduction
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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 S. Tanimoto Perl Introduction
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