Join Bill Weinman for an in-depth discussion in this video The undef function, part of Perl 5 Essential Training.
- [Voiceover] Sometimes it may be neccessary…to remove the value of a variable without…setting it to zero, or another value.…A lot of languages have a concept of a no value,…or some value that's other than what you might…normally find in a numerical or string context.…In Perl this is called undef,…and you use the undef function…to accomplish this, so,…here's a working copy of undef.pl…from chapter 13 of the exercise files,…and you notice that there's a variable…declared here on line 7, $x,…and no value is assigned to it, and so,…when I run this, you'll notice it says x is not defined.…
That's different than x doesn't exist.…If I remove this entirely, I just get an error…that we haven't even declared x.…And so, x exists,…and it has a value,…and that value is undef.…That's the default value,…it is initialized with undef, otherwise,…it would just have some crazy, random number in it,…and so if I give it a value, and run this,…it says x is 42, so we're checking the defined state…of x there in line 9,…with this defined function,…
Watch to learn the details of the Perl syntax, from variables, conditionals, loops, and data structures to regular expressions, functions, and references. A quick-start guide is included for experienced developers who want to get up and running with Perl 5 fast, and the entire course is recommended for both new and experienced programmers alike. Later chapters cover file handling and reusing code with Perl modules, plus Perl best coding practices.
- Understanding Perl's general syntax and the anatomy of a Perl script
- Writing statements and expressions
- Creating assignments
- Working with variables and strings
- Using data types effectively
- Defining logical flow with conditionals and loops
- Using special variables
- Using Perl operators
- Performing simple Perl programming tasks with expressions
- Matching data
- Defining and calling functions
- Using references
- Handling files in the file I/O
- Using built-in functions
- Reusing code with modules
- Coding with Perl best practices
Skill Level Intermediate
1. Setting Up
About Perl3m 36s
2. Quick Start
3. Basic Syntax
4. Values and Variables
7. Special Variables
9. Regular Expressions
11. References and Structures
12. File I/O
13. Built-In Functions
15. Best Practices
- Mark as unwatched
- Mark all as unwatched
Are you sure you want to mark all the videos in this course as unwatched?
This will not affect your course history, your reports, or your certificates of completion for this course.Cancel
Take notes with your new membership!
Type in the entry box, then click Enter to save your note.
1:30Press on any video thumbnail to jump immediately to the timecode shown.
Notes are saved with you account but can also be exported as plain text, MS Word, PDF, Google Doc, or Evernote.