Bug #11793: puts 'ab'.gsub('a', '\\+') - unexpected output

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: ruby 2.2.3p173 (2015-08-18 revision 51636) [x86_64-darwin15]
• Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN

[burnson (William Burnson)]

Test case:

puts 'ab'.gsub('a', '\\+')

Expected output:

\+b

Actual output:

b

The way I understand gsub(pattern, replacement) when used with two string arguments is that it will perform a literal replacement, so it is quite unexpected that substituting with \+ removes the pattern entirely.

Doc: http://ruby-doc.org/core-2.2.3/String.html#method-i-gsub

[burnson (William Burnson)]

• Description updated (diff)

[burnson (William Burnson)]

• Description updated (diff)

[burnson (William Burnson)]

• Description updated (diff)

[burnson (William Burnson)]

• Description updated (diff)

[Hanmac (Hans Mackowiak)]

its because how gsub works you need to escape the \

puts 'ab'.gsub('a', '\\\+') #=> \+b

[usa (Usaku NAKAMURA)]

• Status changed from Open to Rejected

[phluid61 (Matthew Kerwin)]

Substitution parameters work in string-string mode:

irb> puts 'ab'.gsub('a', %q(\`))
b
irb> puts 'ab'.gsub('a', %q(\&))
ab
irb> puts 'ab'.gsub('a', %q(\'))
bb
irb> puts 'ab'.gsub('a', %q(\0))
ab
irb> puts 'ab'.gsub('a', %q(\\0))
ab
irb> puts 'ab'.gsub('a', %q(\\\0))
\0b
irb> puts 'ab'.gsub('a', %q(\\\+))
\+b

I used %q() to make it clear just how many blackslashes are involved.

Note with the \0 examples, either a single or double-backslash invokes the special value replacement.

The plus symbol ($+ or \+) is an alias for the $LAST_PAREN_MATCH special value, which in this case is blank.

[phluid61 (Matthew Kerwin)]

I should have used this example:

puts 'ab'.gsub('a', "\x5C\x5C\x2B")
\+b

[nobu (Nobuyoshi Nakada)]

• Description updated (diff)

The document states "It may contain back-references", \+ is one of them.

Note: preformated text requires a preceding blank line.