Exercise 10: What Was That?

In Exercise 9 I threw you some new stuff, just to keep you on your toes. I showed you two ways to make a string that goes across multiple lines. In the first way, I put the characters \n (backslash n) between the names of the months. These two characters put a new line character into the string at that point.

This \ (backslash) character encodes difficult-to-type characters into a string. There are various "escape sequences" available for different characters you might want to use. We'll try a few of these sequences so you can see what I mean.

An important escape sequence is to escape a single-quote ' or double-quote ". Imagine you have a string that uses double-quotes and you want to put a double-quote inside the string. If you write "I "understand" joe." then Ruby will get confused because it will think the " around "understand" actually ends the string. You need a way to tell Ruby that the " inside the string isn't a real double-quote.

To solve this problem you escape double-quotes and single-quotes so Ruby knows to include them in the string. Here's an example:

"I am 6'2\" tall."  # escape double-quote inside string
'I am 6\'2" tall.'  # escape single-quote inside string

The second way is by using triple-quotes, which is just """ and works like a string, but you also can put as many lines of text as you want until you type """ again. We'll also play with these.

tabby_cat = "\tI'm tabbed in."
persian_cat = "I'm split\non a line."
backslash_cat = "I'm \\ a \\ cat."

fat_cat = """
I'll do a list:
\t* Cat food
\t* Fishies
\t* Catnip\n\t* Grass

puts tabby_cat
puts persian_cat
puts backslash_cat
puts fat_cat

What You Should See

Look for the tab characters that you made. In this exercise the spacing is important to get right.

$ ruby ex10.rb
        I'm tabbed in.
I'm split
on a line.
I'm \ a \ cat.

I'll do a list:
        * Cat food
        * Fishies
        * Catnip
        * Grass

Escape Sequences

This is all of the escape sequences Ruby supports. You may not use many of these, but memorize their format and what they do anyway. Try them out in some strings to see if you can make them work.

Escape What it does.
\\ Backslash ()
\' Single-quote (')
\" Double-quote (")
\a ASCII bell (BEL)
\b ASCII backspace (BS)
\f ASCII formfeed (FF)
\n ASCII linefeed (LF)
\r ASCII Carriage Return (CR)
\t ASCII Horizontal Tab (TAB)
\uxxxx Character with 16-bit hex value xxxx (Unicode only)
\v ASCII vertical tab (VT)
\ooo Character with octal value ooo
\xhh Character with hex value hh

Study Drills

  1. Memorize all the escape sequences by putting them on flash cards.
  2. Use ''' (triple-single-quote) instead. Can you see why you might use that instead of """?
  3. Combine escape sequences and format strings to create a more complex format.

Common Student Questions

I still haven't completely figured out the last exercise. Should I continue?
Yes, keep going. Instead of stopping, take notes listing things you don't understand for each exercise. Periodically go through your notes and see if you can figure these things out after you've completed more exercises. Sometimes, though, you may need to go back a few exercises and do them again.
What makes \\ special compared to the other ones?
It's simply the way you would write out one backslash (\) character. Think about why you would need this.
When I write // or /n it doesn't work.
That's because you are using a forward-slash / and not a backslash \. They are different characters that do very different things.
I don't get Study Drill 3. What do you mean by "combine" escape sequences and formats?
One concept I need you to understand is that each of these exercises can be combined to solve problems. Take what you know about format strings and write some new code that uses format strings and the escape sequences from this exercise.What's better, ''' or """? Use ''' when you need a multi-line string that contains #{} formatting, but you don't want them to be processed yet or at all. Use """ for all other multi-line strings.

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