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Other special characters

From: Using Regular Expressions

Video: Other special characters

In this movie I just want to make mention of some other special characters that we need to be aware of when we're working with text files. These might not be characters that you would normally think about. First, there are spaces. A space is an actual character as far as a regular expression is concerned. We saw that before when we put spaces in the word car, we saw that it no longer matched anymore. So the space is a character and if you want to match a space, well, you just type a literal space. That's all there is to it. For tabs it's not quite that simple. For tabs you use a backslash t. It's that escape character, but notice now, that escape character is giving t a special meaning.

Other special characters

In this movie I just want to make mention of some other special characters that we need to be aware of when we're working with text files. These might not be characters that you would normally think about. First, there are spaces. A space is an actual character as far as a regular expression is concerned. We saw that before when we put spaces in the word car, we saw that it no longer matched anymore. So the space is a character and if you want to match a space, well, you just type a literal space. That's all there is to it. For tabs it's not quite that simple. For tabs you use a backslash t. It's that escape character, but notice now, that escape character is giving t a special meaning.

Now it's saying, we're looking for a tab character. Instead of trying to type a tab, we just put backslash t, and that matches a tab in the document. It's a control character. There're some other control characters. For line returns it's a little tricky because there are actually three possibilities. It could be \r, \n, or \r followed by \n. r is for line return and n is for new line. So you can have different ones in a file, and a lot of times it depends on whether that file is a Windows file, a UNIX file, a Mac file, or from somewhere else.

So be aware that this matches a new line, but that you do have to worry about all three possibilities. There are some other non-printable characters. You won't come across very much, but they could show up in a document: the bell, escape, form feed, vertical tab, and then there is also ASCII or ANSI codes. These are codes that would appear in typically like a UNIX program or something like that that would control the appearance of the text terminal and the way it would look. They typically look like 0xA9-- that's what the code looks like.

The way you would access that inside a regular expression is with \x to let us know that it's a control code, followed by the A9 portion. So the 0 is always the first character of the code; it just gets replaced by that backslash and then it looks pretty similar. You're not going to run across those very often. It's really the spaces, tabs, and line returns that I want you to be aware of, and also just to make the point that putting the backslash in front of a character that's a literal character doesn't do no harm; it actually does make it look for something different.

So backslash t is not the same thing as a t. Don't think you can harmlessly throw that backslash in there. Let's try a couple of these, just with, let's try space first of all. Obviously we have cat. Let's put spaces in here. If we want to match that with cat, we saw it doesn't match, but if we put the spaces in there, the literal spaces, now it does match. It's that easy. Now it's matching that space. If I instead had something here, like an x, now it doesn't match anymore, right; it has to be that same exact character. Let's try a tab.

Let's say that we have a\tb, and then down here let's type a and hit the Tab key, followed by a b. See that it matches? cdef, see? Let's take away our tab, and let's hit a line return after the c, and now let's change this looking from c to d. It's not a tab in there anymore, now it's a new line, so n worked. r or r\n also could have potentially worked, but in this case it's a new line.

The new line character that JavaScript is using is the backslash n. So c to d gets matched across that new line.

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This video is part of

Image for Using Regular Expressions
Using Regular Expressions

59 video lessons · 11712 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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