Join Bill Weinman for an in-depth discussion in this video Negative conditionals with unless, part of Perl 5 Essential Training.
- [Voiceover] Perl also provides a negative version…of the if statement called unless.…Here's a working copy of conditional.pl from Chapter…five of the exercise files.…And I'm just going to change this here to say…unless, with the unless here, and when…I run this, you notice the condition is true…and so unless is not run and if I change this one…to a seven, and run now, you see unless is…displayed so the condition is false and so unless,…the unless clause is run.…
And likewise, we can have an else here, and if I…change this back to a one, you see the else is run…instead of the unless.…This is not very common.…It's usually clearer to use something like, if x is…not equal to one, what's more common is to…use this in the post fix notation, so we could…do something like, say, these are the same…unless $x is equal…to $y and if…I save and run this, we'll make this not…equal to rather, and then it says these are the same…unless x is not equal to y.…
So the unless statement is simply the inverse of if.…It works just like if except the…
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
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