Backslashes in single quoted strings vs. double quoted strings

Question

If I add a backslash+space to the start of double and single quoted strings, I get different results:

"\ text" '\ text'  

In the output for the double quoted string I see only a space.
In the output for the single quoted string I see backslash+space.

What's happening there? Is this because '\ ' is interpreted as a special character in the double quote string but in the single quoted string the characters are preserved as is?

If I change the strings to this, I see the same output, namely a single slash followed by a space and then the text:

"\\ text" '\\ text'  

In both cases the backslash is escaped. I'm confused why they work the same way in this situation.

Is there some rule that would help to explain the fundamental difference between how single quoted strings and double quoted strings handle backslashes in Ruby?

Answer 1

Double-quoted strings support the full range of escape sequences, as shown below:

• \a Bell/alert (0x07)
• \b Backspace (0x08)
• \e Escape (0x1b)
• \f Formford (0x0c)
• \n Newline (0x0a)
• \r Return (0x0d)
• \s Space (0x20)
• \t Tab (0x09)
• \v Vertical tab (0x0b)

For single-quoted strings, two consecutive backslashes are replaced by a single backslash, and a backslash followed by a single quote becomes a single quote:

'escape using "\\"' -> escape using "\" 'That\'s right'     -> That's right 

Answer 2

Ruby only interprets escape sequences in double quoted strings. In a single quoted string, only \\ (backslash backslash) and \' (backslash quote) are taken as special characters. You should use double quoted strings only when you need more interpretation. Otherwise, single quotes provide a performance boost.

When you mentioned including the name of a variable, Ruby never does that. Just the variable name is treated as more of the string literal. To include the value of a variable (or any expression) put the expression in like this:

"#{variable}" 

Note that this only works in double quoted strings. To add a variable to a single quoted one, you need to do this:

'The value of X is: '+X 

If you need serious formatting, look into Ruby's version of sprintf and printf. They are pretty much wrappers around the C functions, and are quite powerful, but a bit cumbersome to use.