To understand the bug, try this:
There is no bug.
irb(main):009:0> "matt's test".sub(/(')/, '\1')
=> "matt's test"
The 'single ticks' interpret \1 as a literal \ and a 1, not an escape. Then
.sub sees the \1, and replaces it with the 1nth (grouping) from the Regexp -
which is a literal tick '.
Now try it with "double quotes":
irb(main):005:0> "matt's test".sub(/(')/, "\\1")
=> "matt's test"
The " forces us to escape the \ as \\ to get a literal \.
And a literal \ in a replacement string is a meta character. To get a
literal in a replacement, you need \\ in the string and consequently
\\\\ in a double quoted string.
So your \\' indeed goes in as a literal \'. But the group replacer still
sees a \, and snarfs it, expecting a number after it. I would call that a
bug (essentially because I might personally be capable of correctly parsing
a \1!)
No, this is not a bug and it is not the "group replacer". The
replacement string is parsed by the regexp engine and since the
backslash does not escape a character that has meta capabilities (such
as & and 1..9) it is silently discarded.
Untill someone dissects the source and finds (or adds) a better fix, here's
a workaround:
irb(main):012:0> "matt's test".sub(/'/){"\\'"}
=> "matt\\'s test"
No, the proper way to do it is this:
irb(main):002:0> "matt's test".sub(/'/, "\\\\'")
=> "matt\\'s test"
irb(main):003:0> puts "matt's test".sub(/'/, "\\\\'")
matt\'s test
=> nil
irb(main):006:0> "matt's test".sub(/'/, '\\\\\'')
=> "matt\\'s test"
irb(main):007:0> puts "matt's test".sub(/'/, '\\\\\'')
matt\'s test
=> nil
Blocks are only needed if you need to do some calculations based on the
match, e.g.
irb(main):008:0> "There is 1 number in this string".gsub(/\d+/) {|m|
m.to_i * 34}
=> "There is 34 number in this string"
That surprised me too, because I thought that sub's block form also
interpolated \n group inserters, but I suppose that blocks have room for
true $1 match references.
Yes.
\1 is often available in some regular expressions
that cram all the searchers and replacers into one huge line, so a $1 is
naturally not available inside its own source expression. (I also don't
happen to know if Ruby supports such super-regices!)
I am not sure what you mean here. The reason $1 cannot be used in
regular expressions and replacement strings is that it is a variable
that gets its value before the regexp is created (of course you can use
it but it cannot refer to matching of the regexp you put it into).
You can use groups inside the regular expression as well as in the
replacement string if this is what you mean.
irb(main):017:0> "aba abc".gsub(/(.)(b)\1/, "[\\1]<\\2>[\\1]")
=> "[a]<b>[a] abc"
Kind regards
robert
