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Metacharacters

From: Using Regular Expressions

Video: Metacharacters

In the last movie we learned about literal characters, the fact that an A matches an A and a B matches a B and so on. Now, we're going to talk about metacharacters, and that's really the alternative. If it's not a literal character, it's a metacharacter--a character that has special meaning. Sometimes they work a little bit like mathematical operators. What they do is they transform literal characters into powerful expressions. There are only a few metacharacters to learn. We're going to be working with these throughout the rest of the tutorial. Basically everything else that you need to know about regular expressions besides literal characters is how do these metacharacters all work, what do they do? And it's complicated, only slightly, because they can have more than one meaning.

Metacharacters

In the last movie we learned about literal characters, the fact that an A matches an A and a B matches a B and so on. Now, we're going to talk about metacharacters, and that's really the alternative. If it's not a literal character, it's a metacharacter--a character that has special meaning. Sometimes they work a little bit like mathematical operators. What they do is they transform literal characters into powerful expressions. There are only a few metacharacters to learn. We're going to be working with these throughout the rest of the tutorial. Basically everything else that you need to know about regular expressions besides literal characters is how do these metacharacters all work, what do they do? And it's complicated, only slightly, because they can have more than one meaning.

It's really dependent on how we use the symbol in context, so we'll be taking a look at that. It's also these metacharacters that have variation between the different regex engines. Now as far as metacharacters go, one thing I want to point out to is that unlike where we just had C-A-R, if we have a metacharacter in there, it also highlights that for us in regexPal. So that's very helpful. It helps us to really see, ah! Here is a bracketed expression, here's the one in parentheses, this is a metacharacter, and it really differentiates them from the literal characters, which don't get colored at all.

That's actually an option here. You can turn off highlighting regex syntax if you don't want it, but I find this pretty helpful, so I usually leave that option on here for Highlight regex syntax. Now one thing I want to notice that I have found when I'm working with regexPal getting ready for this course that sometimes when you paste code into the window, the highlighting isn't quite right right away. And if that happens to you and for some reason the highlighting is not right, all you need to do is hit a space and then erase it again, and it will sort it out. That's all it takes just to make sure that it recovers from that paste.

Let's just put in a new keystroke and take it away again and then the highlighting should come back to the way it ought to be. All right! Now that we know what metacharacters are. We've seen how the highlighting works. Let's dive into learning our first metacharacter, probably the most important one, the wildcard metacharacter.

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This video is part of

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Using Regular Expressions

59 video lessons · 12514 viewers

Kevin Skoglund
Author

 
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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 26s
    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 30s
    6. POSIX bracket expressions
      4m 13s
  5. 36m 38s
    1. Repetition metacharacters
      7m 17s
    2. Quantified repetition
      6m 59s
    3. Greedy expressions
      6m 27s
    4. Lazy expressions
      6m 46s
    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 31s
    1. Positive lookahead assertions
      6m 39s
    2. Double-testing with lookahead assertions
      7m 16s
    3. Negative lookahead assertions
      6m 10s
    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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