Table of Contents

• Home
• Introduction
• Introduction
• This tutorial is...
• This tutorial is not...
• How to Use...
• The Table of Contents
• Conventions used in this Tutorial
• What you need to know
• Use of this document
• Personal Printouts
• Intranet usage
• Mirroring
• Translations
• A Short Introduction To Perl
• A Short Introduction To Perl
• What is Perl?
• What is ActivePerl? Are the other Perls inactive?
• Can I run Perl on my computer?
• What can I do with Perl ?
• The Internet
• Systems Administration
• What can't I do with Perl ?
• Support
• Setup
• Setup
• 1. Getting the Software
• 2. Installation
• 3. Testing - Your First Perl Script
• The Tutorial: The Journey Begins
• The Tutorial: The Journey Begins
• Your First Time
• What if it doesn't...?
• Assuming it's now all right...
• Shebang
• Variables
• Scalars
• $ % @ are Good Things
• Typing
• Variable Interpolation
• Changing Variables
• Auto(de|in)crements
• Escaping
• Context: About Perl and @^$%&~`/?
• Strings and Increments
• Print: A List Operator
• Subroutines -- A First Look
• Comments
• Comparisons
• Comparisons
• An iffy start
• The Truth According to Perl
• Equality and Perl
• All Equality is Not Equal: Numeric versus String
• An interlude -- The Perl Motto
• The Comparison Operators Listed
• The Golden Rule of Comparisons
• More About If: Multiples
• elsif
• User Input
• User Input
• STDIN and other filehandles
• Chop
• Safe Chopping with Chomp
• Arrays
• Arrays
• Lists, herds -- what are arrays?
• Basic Array Work
• Elements of Arrays
• How to refer to elements of an array
• More ways to access arrays
• For Loops
• A for Loop demonstrated
• For loops with .. , the range operator
• foreach
• The infamous $_
• A Premature End to your loop
• A little more control over the premature ending: Labels
• Changing the Elements of an Array
• Jiggerypokery with Arrays
• A table of array hacking functions
• Splice
• Deleting Variables
• Deleting Variables
• False values versus Existence: It is, therefore...
• Basic Regular Expressions
• Basic Regular Expressions
• An introduction
• Senstivity -- regexes in touch with their inner child
• Character Classes
• Matching at specific points
• Negating the regex
• Returning the Match
• * + -- regexes become line noise
• The Difference Between + and *
• Re-using the match -- \1, $1...
• How to Avoid Making Mountains while Escaping Special Characters
• Subsitution and Yet More Regex Power
• Subsitution and Yet More Regex Power
• Basic changes
• \w
• Replacing with what was found
• x
• More Matching
• Parentheses Again: OR
• (?: OR Efficiency)
• Matching specific amounts of...
• Pre, Post, and Match
• RHS Expressions
• /e
• /ee
• A Worked Example: Date Change
• Split and Join
• Split and Join
• Splitting
• A very FAQ
• What Humpty Dumpty needs : Join
• A recap, but with some new functions
• A recap, but with some new functions
• Randomness
• Concatenation
• Files
• Files
• Opening
• An unforgivable error
• \\ or / in pathnames -- your choice
• Reading a file
• Writing to a File
• A simple write
• Appending
• @ARGV: Command Line Arguments
• Modifying a File with $^I
• $/ -- Changing what is read into $_
• HERE Docs
• Reading Directories
• Reading Directories
• Globbing
• readdir : How to read from directories
• Associative Arrays
• Associative Arrays
• The Basics
• A Hash in Action
• When you should use hashes
• Hash Hacking Functions
• More Hash Access: Iteration, keys and values
• Sorting
• Sorting
• A Simple Sort
• Numeric Sorting -- How Sort Really Works
• Sorting Multiple Lists
• Grep and Map
• Grep and Map
• Grep
• Map
• Writing your own grep and map functions
• External Commands
• External Commands
• Some ways to...
• Exec
• System
• Backticks
• When to use external calls
• Opening a Process
• Quote execute
• Oneliners
• Oneliners
• A short example
• File access
• Modifying files with a oneliner and $^I
• Subroutines and Parameters
• Subroutines and Parameters
• Parameters
• Namespaces
• Variable Scope
• my Variables
• Multiple Returns
• Local
• Returning arrays
• Modules
• Modules
• An introduction
• File::Find -- using a module
• ChangeNotify
• Your Very Own Module
• Bondage and Discipline
• Bondage and Discipline
• -w
• Shebang
• use strict;
• Debugging
• Logical Operators
• Logical Operators
• or
• Precedence: What comes First
• And
• Other Logical Operators
• Last words
• Thanks to...

Variable Interpolation

We still haven't finished learning from that humble bit of code. To refresh your memory, here it is again:

$string="perl";
$num1=20;
$num2=10.75;
print "The string is $string, number 1 is $num1 and number 2 is $num2\n";

Notice the way the variables are used in the string. Sticking     variables inside of strings has a technical term - "variable     interpolation". Now, if we didn't have the handy $ prefix for we'd have to do something like     the example below, which is pseudocode. Pseudocode is code to demonstrate a    concept, not designed to be run. Like certain Microsoft software.   

print "The string is ".string." and the number is ".num."\n";

which is much more work. Convinced about those prefixes yet ?

Try running the following code:

$string="perl";
$num=20;
print "Doubles: The string is $string and the number is $num\n";
print 'Singles: The string is $string and the number is $num\n';
   

Double quotes allow the aforementioned variable interpolation. Single quotes do not. Both have their uses as you will see later, depending on whether you wish to interpolate anything.