How to add a single backslash character to a string in Ruby?

Question

I want to insert backslash before apostrophe in "children's world" string. Is there a easy way to do it?

irb(main):035:0> s = "children's world"
=> "children's world"
irb(main):036:0> s.gsub('\'', '\\\'')
=> "childrens worlds world"

Answer 1

from ruby-doc.org about the replacement pattern for gsub :

the sequences \\1, \\2, and so on may be used to interpolate successive groups in the match

This includes the sequence \\' , which means "everything following what I matched".

Either "\\\\'" or '\\\\\\'' will both produce \\' (remember that \\ has to be escaped in both double and single quoted strings, and that ' has to be escaped in single-quoted strings, so using single-quotes in this case actually makes things more verbose). Eg:

puts "before*after".gsub("*", "\\'")
"beforeafterafter"

puts "before*after".gsub("*", '\\\'')
"beforeafterafter"

What you want gsub to see then is actually \\\\' , which can be produced by both "\\\\\\\\'" and '\\\\\\\\\\'' . So:

puts s.gsub("'", "\\\\'")
children\'s world

puts s.gsub("'", '\\\\\'')
children\'s world

or if you have to do a lot with \\ you could take advantage of the fact that when you use /.../ (or %r{...} ) you don't have to double-escape the backslashes:

puts s.gsub("'", /\\'/.source)
children\'s world

Answer 2

>> puts s.gsub("'", "\\\\'")
children\'s world

Answer 3

Your problem is that the string "\\'" is meaningful to gsub in a replacement string. In order to make it work the way you want, you have to use the block form.

s.gsub("'") {"\\'"}