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Character ranges

From: Using Regular Expressions

Video: Character ranges

In the last movie we talked about character sets and we saw how if you were writing a character set that was for let's say all capital letters, you would have to type out A, B, C, D, and so on, all the way till you got the Z. It's a lot of typing. Character ranges are going to help us solve that problem, by giving us a convenient shortcut by using the dash metacharacter to indicate a range of characters. So it's basically just a shorthand to keep you from having to do all of that typing. So it represents all characters that are between a starting character and an ending character. Now the dash is only a metacharacter when it's inside a character set; outside the character set it's just a literal dash.

Character ranges

In the last movie we talked about character sets and we saw how if you were writing a character set that was for let's say all capital letters, you would have to type out A, B, C, D, and so on, all the way till you got the Z. It's a lot of typing. Character ranges are going to help us solve that problem, by giving us a convenient shortcut by using the dash metacharacter to indicate a range of characters. So it's basically just a shorthand to keep you from having to do all of that typing. So it represents all characters that are between a starting character and an ending character. Now the dash is only a metacharacter when it's inside a character set; outside the character set it's just a literal dash.

Okay, so this really is just about character sets. So for example, instead of writing out all the numbers 0 to 9, we can just abbreviate that by saying 0-9. Now obviously the position is important because what we're saying is starting with 0m go up to 9. We could also have 5-9 or 3-7, but it tells us it's a range from the starting character till we get to the ending character. We can do the same thing with the alphabet. We can A-Z and then we can have immediately after it a-z lowercase, It's still telling us, look, all the characters A- Z capitalized, all the characters a-z lowercase are inside this character set. And of course, we could even break it up, a-e, k-o, and u-y.

So in the end that will have fifteen characters represented inside our character set, exactly as if we type them all out. Now one word of caution though is when you're working with numbers, 50-99 is not all numbers from 50 to 99. We're looking at text here, not numbers; this is just text. It doesn't have its same meaning. If we say 50-99, that's the same thing as saying 0 to 9, because what we're saying is this set includes the number 5, then it includes all numbers 0-9, and it also includes the number 9. That's our character set.

We've just repeated ourselves with the 5 and the 9 on either end, so be careful about that. Integers do not increment the way that you normally think that they would in math, right. This is not computer programming; we're just representing the actual characters that are there on the screen. This is one single character made up with this character set. Now it might be possible to do a range of characters with things like punctuation, but since the order of those really isn't that obvious, you probably would get unexpected results, and so you really shouldn't do it. Really what you're going to use it for are these that have an obvious progression--the numbers and the letters. Let's try a few.

So first in the example before, remember we typed out all of this? Well, instead we can just shorten all that down to just saying, well, everything from A-Z. That gives us our same match; it's the exact same thing, completely equivalent. Much easier. If we wanted to match all lowercase letters too--let's take away that ello there and just do a-z-- now see, it matches every letter, whether it's uppercase or lowercase. We've defined a character set that's case insensitive. As another example, let's say that we had a phone number here. Let's say we have 555-666-7890. Okay, so it's a phone number in America that has that format.

So if we wanted to write a regular expression that would match that--let's erase this--we want to have a character set, and inside that character set we want to match all digits 0-9. That's what's allowed to be in our character set. Now if we want to match the exact set, not just a single character, we would do, paste it in again and again--that matches the first three numbers--followed by a dash. You can see where it match those followed by three more numbers, followed by a dash, followed by four more numbers. Now we're going to see some even better ways to do this in the future, this really raw simplistic version now, before we start learning how to do things like repetition.

Let's say that we had a ZIP code, 90210, that's a very famous Beverly Hills zip code. Same thing, we just take out the dashes here and make it just five characters long and now it matches the zip code. In other countries, you are allowed to have things besides just numbers; in the US we only have numbers, but in other countries you might have something like WC2H 9AW in London. To match something like that, think for a second about how we'd match it. Let's back up. Let's simplify it. That matches the 2 and the 9, but it doesn't matches the letters.

Let's assume it's all uppercase, so A-Z will now match all those letters. Now we can just copy that, and let's assume for a moment that it has four characters, a space, and three characters, so we would have four of those, a space, and then three more of those, and now it matches. So you see it's much simpler than having to type that out. Imagine if I try to type 0-9 and A-Z all of those times for each one of those, so it does save you a lot of typing, and that's really the real purpose of ranges.

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This video is part of

Image for Using Regular Expressions
Using Regular Expressions

59 video lessons · 11676 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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