Intro to Perl
- 1. Perl A STEP UP FROM BASH
- 2. Perl’s Creator: Larry Wall • LarryWall, programmer, linguist, author, born March 10, 1949 in Duncan, British Columbia, Canada. Perl computer language creation in 1987. • Quotes: • The three chief virtues of a programmer are: Laziness, Impatience and Hubris • There's MoreThan OneWay to Do It • Add your first bullet point here • Add your second bullet point here • Add your third bullet point here
- 3. What is Perl Practical Extraction and Reporting Language Pathologically Eclectic Rubbish Lister “Perl” is the language “perl” is the compiler Never “PERL” • Perl is a general-purpose programming language originally developed for text manipulation and now used for a wide range of tasks including web development, system administration, network programming, code generation and more. • It's intended to be practical rather than beautiful. • Supports both procedural and OO programming. • It has one of the world's most impressive collections of third-party modules (http://www.cpan.org).
- 4. The Perl philosophy • There’s more than one way to do it. • Share and Enjoy! • General Purpose Programming Language • Open Source • Fast • Flexible • Secure • Fun • Cross Plaform • Large active user base • Can look complicated, initially, particularly if you're not familiar with regular expressions
- 5. Interpreting Perl • In a File • print “This is AWESOMMMMMEEEEEEEE!n”; • On command line: perl script.pl • #!/usr/bin/perl • print “This is AWESOMMMMMEEEEEEEE!n”; • On Command line ./script.pl • On the shell • perl –e ‘print “This is AWWEESSSOOMMEEEEEn” ’
- 6. Perl Syntax Overview • White space is ignored • Perl statements end with a semi- colon. print ("Hello, world!"); • Comments start with a # and run to the end of the line. # This is a comment • Double quotes or single quotes may be used around literal strings: print("Hello, world!"); print ('Hello, world!'); • However, only double quotes interpolate variables and special characters such as newlines (n): • Scalar variables start with a $ • Question: What is a scalar value? • “ ” • ‘ ’ • 42 • .0001 • 3.27e17 • Perl will automatically convert between types as required. • print('3' + 4.5); # prints 7.5 • Concatenation:Arithmetic operators Vs. .
- 7. Time Out to Code
- 8. Unique to Perl PRAGMAS • Perl is a permissive language • A way to impose discipline is with pragmas. • A pragma is a directive to the interpreter informing it about some form of I/O with the code. • use warnings; # display warnings • use strict; #more restrictive to assist in identification of mistakes SPECIAL VARIABLES • There are some ‘magic’ variables. These special variables are used for all kinds of purposes. • $_: is the ‘default variable’. • @ARGV: the command line arguments to your script. • $ARGV: contains the name of the current file when reading from <> or readline(). • @_: the arguments passed to a subroutine. • $a, $b: Special package variables when using sort(). • $/:The input record separator, newline by default.
- 9. Conditional Constructs • The COND shall be conditional statement surround by ( and ), and BLOCK shall be one ore more statements surround by { and }. • if ( is_valid( $value ) ) { … } elsif (cond) { ...} else { ...} • Ex. if ($zippy) { print("Yow!"); }
- 10. Arithmetic and String Operators ARITHMETIC OPERATORS Standard arithmetic operations Less standard operations modulus (%), exponentiation (**) $area = $pi * ($radius ** 2); Often need to do things like $total = $total + $amount; Can be abbreviated to $total += $amount; Even shorter $x++; $y--; Question:What is the subtle difference between $x++ and ++$x? STRING OPERATORS Concaternation (.) $name = $firstname . ' ' . $surname; Repetition (x) $line = '-' x 80; $police = 'hello ' x 3; Shortcut versions available $page .= $line; # $page = $page . $line $thing x= $i; # $thing = $thing x $i
Editor's Notes
- #9: Strict enforces that variables begin with a my so it can identify when variables have not been declared. Variables can be created whenever in a script and sometimes by accident, like with files in Linux, so to enforce a stricter policy use the strict pragma and now you have to declare variables with a my or it will notify you that a variable has not been declared.