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Installing an engine


From:

Using Regular Expressions

with Kevin Skoglund

Video: Installing an engine

In the last movie, we took a look at a number of different regex engines. Now we need to install an engine of our own that we can use as we explore the regular expression syntax. There are a number of different tools that we could choose. Let's take a look at some of them. First, there is grep and egrep. You remember that those are UNIX tools, offered some of the earliest support for regular expressions. And if you have UNIX, Linux, or Mac OS X, then you already have those tools installed. The problem with them is because they were some of the earliest implementations of regular expressions, they don't have a lot of the advances that Perl brought.
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  1. 2m 18s
    1. Welcome
      56s
    2. Using the exercise files
      1m 22s
  2. 19m 55s
    1. What are regular expressions?
      3m 20s
    2. The history of regular expressions
      6m 40s
    3. Regular expression engines
      2m 44s
    4. Installing an engine
      4m 5s
    5. Notation conventions and modes
      3m 6s
  3. 21m 23s
    1. Literal characters
      6m 39s
    2. Metacharacters
      2m 1s
    3. The wildcard metacharacter
      4m 31s
    4. Escaping metacharacters
      4m 53s
    5. Other special characters
      3m 19s
  4. 31m 27s
    1. Defining a character set
      5m 49s
    2. Character ranges
      4m 49s
    3. Negative character sets
      4m 53s
    4. Metacharacters inside character sets
      5m 12s
    5. Shorthand character sets
      6m 31s
    6. POSIX bracket expressions
      4m 13s
  5. 36m 39s
    1. Repetition metacharacters
      7m 17s
    2. Quantified repetition
      6m 59s
    3. Greedy expressions
      6m 27s
    4. Lazy expressions
      6m 47s
    5. Using repetition efficiently
      9m 9s
  6. 20m 24s
    1. Grouping metacharacters
      4m 14s
    2. Alternation metacharacter
      4m 54s
    3. Writing logical and efficient alternations
      7m 33s
    4. Repeating and nesting alternations
      3m 43s
  7. 19m 19s
    1. Start and end anchors
      7m 21s
    2. Line breaks and Multiline mode
      4m 41s
    3. Word boundaries
      7m 17s
  8. 23m 33s
    1. Backreferences
      8m 57s
    2. Backreferences to optional expressions
      3m 51s
    3. Finding and replacing using backreferences
      7m 16s
    4. Non-capturing group expressions
      3m 29s
  9. 32m 32s
    1. Positive lookahead assertions
      6m 39s
    2. Double-testing with lookahead assertions
      7m 16s
    3. Negative lookahead assertions
      6m 11s
    4. Lookbehind assertions
      6m 26s
    5. The power of positions
      6m 0s
  10. 13m 13s
    1. About Unicode
      4m 19s
    2. Unicode in regular expressions
      4m 41s
    3. Unicode wildcards and properties
      4m 13s
  11. 1h 55m
    1. How to use this chapter
      5m 38s
    2. Matching names
      6m 33s
    3. Matching postal codes
      8m 54s
    4. Matching email addresses
      5m 0s
    5. Matching URLs
      8m 1s
    6. Matching decimal numbers and currency
      6m 45s
    7. Matching IP addresses
      7m 10s
    8. Matching dates
      7m 49s
    9. Matching times
      8m 59s
    10. Matching HTML tags
      8m 34s
    11. Matching passwords
      6m 49s
    12. Matching credit card numbers
      9m 36s
    13. Finding words near other words
      6m 38s
    14. Formatting with Search and Replace, pt. 1
      7m 22s
    15. Formatting with Search and Replace, pt. 2
      4m 15s
    16. Formatting with Search and Replace, pt. 3
      7m 10s
  12. 47s
    1. Goodbye
      47s

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Watch the Online Video Course Using Regular Expressions
5h 36m Intermediate Nov 21, 2011

Viewers: in countries Watching now:

Learn how to find and manipulate text quickly and easily using regular expressions. Author Kevin Skoglund covers the basic syntax of regular expressions, shows how to create flexible matching patterns, and demonstrates how the regular expression engine parses text to find matches. The course also covers referring back to previous matches with backreferences and creating complex matching patterns with lookaround assertions, and explores the most common applications of regular expressions.

Topics include:
  • Creating flexible patterns using character sets
  • Achieving efficiency when using repetition
  • Understanding different types of search strategies
  • Writing logical and efficient alternations
  • Capturing groups and reusing them with backreferences
  • Developing complex patterns with lookaround assertions
  • Working with Unicode and multibyte characters
  • Matching email addresses, URLs, dates, HTML tags, and credit card numbers
  • Using search and replace to format a document
Subject:
Developer
Software:
Regular Expressions
Author:
Kevin Skoglund

Installing an engine

In the last movie, we took a look at a number of different regex engines. Now we need to install an engine of our own that we can use as we explore the regular expression syntax. There are a number of different tools that we could choose. Let's take a look at some of them. First, there is grep and egrep. You remember that those are UNIX tools, offered some of the earliest support for regular expressions. And if you have UNIX, Linux, or Mac OS X, then you already have those tools installed. The problem with them is because they were some of the earliest implementations of regular expressions, they don't have a lot of the advances that Perl brought.

So with Perl-compatible regular expressions, we're going to get a few extra features, but I would say grep and egrep are probably the biggest category of exceptions to some of the syntax that we're going to learn. So they aren't a great tool to use. There's a number of text editors that you could use: TextMate for Mac, E-TextEditor for Windows, BBEdit, EditPad Pro. There are many more text editors out there and IDEs--you certainly can use those. Most text editors have regular expression support, so you can just search a page of text and find out whether it has a match or not.

Now take note that these are text editors, not word processors. Something like Microsoft Word is a bad choice for working with regular expressions. It doesn't offer regular expression support. These are really designed to be code editors used by programmers who usually know about regular expressions, not consumers who usually don't know about regular expression, so make note of that difference. There's also a number of tools that are designed to help you write regular expressions and really show you more about what's going on. PowerGREP, regexBuddy, and regexMagic, these are all excellent tools.

The problem with them is that they're not cross platform. They either work on Mac or Windows, but not on both. As we saw in the last movie, there's also a number of programming languages that use regular expressions, and if you're an expert in one of those, you certainly could use each one of those to test out regular expressions. But I do want to require students of this course to learn one of those languages just to learn regular expressions. There's no need to do that. And some of you may be coming here with a .NET background, while someone else is coming here with a Ruby background. There are a number of different mobile applications that you could use for designing your regular expressions. For example, there are iPhone apps that will help you to craft them.

But for this course, what we wanted everyone to work with was something that was easy to install and cross platform, so that everyone would have a similar experience. So what we've decided on was JavaScript, and there is actually a really great online JavaScript version for working with regexes, and it's called regexPal. So regexpal.com will take you there--that's the online version. And because the creator of the site was kind enough to provide it as open source code, we've included a copy with the files for this course as well. Let's take a look at both.

So here I am, at regexPal. This is the online version. You can see that here's the space where you would enter your regular expression, and here is the space where you would enter the data that you want to test to see if it matches the regular expression or not. I want you to notice just a couple more things about it. Notice there's these three boxes up here, checkboxes, that change things about the way the search works. We'll talk about those later, but just notice that there's three boxes at the top. And then over here is Quick Reference, which will give you some of the syntax that we're learning, in case you forget them, so those are both really helpful.

Now let's take a look at the offline version in the free exercise files. Now, this folder, regexpal, you could just drop the folder into your website's directory and turn on your local web sharing and bring it up that way inside a browser, but there's no need to. This is just basic HTML and JavaScript, so you should be able to just drag index.html or open it up with your browser and then just open it right up and bring everything up. Now mine is mostly the same as what you saw online. There are a couple of differences. I've made the font bigger so it's easier for you to read, and you'll see that now I have four checkboxes up here.

This checkbox here wasn't exposed in his version. It's actually there, but hidden. I've exposed it so that we can actually work with that, and that's the global, whether we want to search globally or not; but other than that, it's basically the same thing. So I'm going to encourage everyone to use the free exercise file version so we have the same thing in front of us, but you'll have the online version as a fallback.

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