CS 105 Perl:
Course Introduction
Nathan Clement
13 May 2014
Agenda
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Course overview
Review syllabus
Informal survey
Next class: paper survey
Perl introduction
Perl origins
Larry Wall
• Graduate study in linguistics
• System administrator at NASA
• Perl 1.0 in 1987
Perl 1.000
NAME
perl | Practical Extraction and Report Language
SYNOPSIS
perl [options] filename args
DESCRIPTION
Perl is a interpreted language optimized for scanning arbitrary text files, extracting information from those text
files, and printing reports based on that information. It's
also a good language for many system management tasks. The
language is intended to be practical (easy to use, efficient, complete) rather than beautiful (tiny, elegant,
minimal). It combines (in the author's opinion, anyway)
some of the best features of C, sed, awk, and sh, so people
familiar with those languages should have little difficulty
with it. (Language historians will also note some vestiges
of csh, Pascal, and even BASIC|PLUS.)
Expression syntax
corresponds quite closely to C expression syntax. If you
have a problem that would ordinarily use sed or awk or sh,
but it exceeds their capabilities or must run a little faster, and you don't want to write the silly thing in C, then
perl may be for you. There are also translators to turn
your sed and awk scripts into perl scripts.
OK, enough
hype.
Perl over time
Path to Maturity
• Perl 1.000 – December 18, 1987
• Perl 2.000 – June 5, 1988
• Perl 3.000 – October 18, 1989
• Perl 4.000 – March 21, 1991
• Perl 5.000 – October 18, 1994
– “Complete rewrite”
• Perl 6.000 - ???
– Project announced on July 19, 2000
– “eventually evolved into a separate language”
Perl over time
Path to Maturity
• Perl 1.000 – December 18, 1987
• Perl 2.000 – June 5, 1988
• Perl 3.000 – October 18, 1989
• Perl 4.000 – March 21, 1991
• Perl 5.000 – October 18, 1994
– “Complete rewrite”
– “Perl” means Perl5
Getting the name right
• Perl
– Not PERL
– The language is Perl
– The interpreter is perl
– Originally named Pearl
– Some “backronyms” are in common use
• Practical Extraction and Report Language
• Pathologically Eclectic Rubbish Lister
More Perl culture
• There’s more than one way to do it
(TMTOWTDI)
– Golfing
– Conciseness
– Terseness
– Obfuscation
Do What I Mean
Do What I Mean (DWIM)
The evolution of DWIM:
DWIM → DWIMmy → dwimmy
“perl dwimmy” on Google:
• “So non-dwimmy open variants are a good idea to
keep around”
• “Non-dwimmy hyperoperator”
• “I don’t think this is DWIMMY at all.”
• “that seems to be pretty dwimmy”
Programming Taxonomy:
Where Perl Fits In
Perl…
• is interpreted
– Compiled at runtime into bytecode
– Bytecode is interpreted
• is dynamically typed
– Variables don’t have types
– Values have types
• has automatic memory management
– Memory is not allocated by the programmer
– No malloc/free, new/delete analogue
These features are typical of “scripting languages”
Programming Taxonomy:
Perl’s Relatives
Just a few similar languages:
• Python
• PHP
• Ruby
So Why Perl?
Perl
PHP
Python
What is Perl good for?
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Text processing
Data manipulation (“munging”)
Quick development of tools
One-offs
System integration
“Glue” code
Databases, Web, etc.
“Real” systems
What is good about Perl?
• Very quick development
– Once you learn it
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Easy things are easy, and typically short
Great documentation
Lots of books
Installed out of the box on many Unix platforms
– or easily available as a package
• Typically comes “batteries included”
– Especially since Perl 5.8 (2002)
• Huge collection of free modules (CPAN)
Your first Perl program
• Create a file
– Open your editor
– Save an empty file
• In another terminal, type perl that-file
– This is one way to run your program
Your second Perl program
Type the following:
print "Some boring text\n";
Save your file and run it.
Running Your Program Directly (1)
We don’t want to type
perl your-program
We’d rather type
./your-program
Running Your Program Directly (2)
Very first line
At the top of your program, type the following:
#!/usr/bin/perl
“Hash-bang” line
This tells the program loader how to run your program.
From a terminal (outside your editor), type
chmod +x your-program
This marks the file as executable so Unix will allow it to execute.
Homework
Write your own Hello, World program that I can run like
./foo.
I don’t care what you print out, as long as it prints
something.
This will require:
• getting a Unix account
• learning the rudimentary features of an editor
• writing one correct Perl statement
• learning how to use turnin
Homework Due Date
• Assignment 1 is due Wednesday, January 22,
but I recommend completing it ASAP.