Replacing `\` with `\\` in ruby

Question

I'm trying to replace all occurrences of \ with \\. Here was my first try:

> puts '\\'.gsub('\\', '\\\\')
\

I was pretty surprised when I saw the output. After some experimenting I was finally able to do what I wanted this this code:

> puts '\\'.gsub('\\', '\\\\\\')
\\

Why isn't the first piece of code working? Why do I need six backslashes?

Answer 1

'\\'.gsub('\\', '\\\\')

When the substitution occurs, the substitution string '\\\\' is passed by the Regexp engine, and \\ is replaced by \. The substitution string ends up as '\\', a single backslash.

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The idomatic way to replace any single bachslach to double is to use:

str.gsub(/\\/, '\\\\\\\\\')  # 8 backslashes!

Answer 2

A bit shorter

'\\'.gsub(/(\\)/, '\1\1')

Answer 3

You may also use Regexp.escape to escape your \:

puts '\\'.gsub('\\', Regexp.escape('\\\\'))