Question

Using Ruby I’m trying to split the following text with a Regex

~foo\~\=bar =cheese~monkey 

Where ~ or = denotes the beginning of match unless it is escaped with \

So it should match

~foo\~\=bar 

then

=cheese 

then

~monkey 

I thought the following would work, but it doesn’t.

([~=]([^~=]|\\=|\\~)+)(.*) 

What is a better regex expression to use?

edit To be more specific, the above regex matches all occurrences of = and ~

edit Working solution. Here is what I came up with to solve the issue. I found that Ruby 1.8 has look ahead, but doesn’t have lookbehind functionality. So after looking around a bit, I came across this post in comp.lang.ruby and completed it with the following:

# Iterates through the answer clauses def split_apart clauses   reg = Regexp.new('.*?(?:[~=])(?!\\\\)', Regexp::MULTILINE)    # need to use reverse since Ruby 1.8 has look ahead, but not look behind   matches =  clauses.reverse.scan(reg).reverse.map {|clause| clause.strip.reverse}    matches.each do |match|     yield match   end end 

Answer 1

What does ‘remove the head’ mean in this context?

If you want to remove everything before a certain char, this will do:

.*?(?<!\\)=      // anything up to the first '=' that is not preceded by '\' .*?(?<!\\)~      // same, but for the squiggly '~' .*?(?<!\\)(?=~)  // same, but excluding the separator itself (if you need that) 

Replace by ”, repeat, done.

If your string has exactly three elements ('1=2~3') and you want to match all of them at once, you can use:

^(.*?(?<!\\)(?:=))(.*?(?<!\\)(?:~))(.*)$  matches:  \~foo\~\=bar =cheese~monkey          |      1      |   2  |  3   | 

Alternatively, you split the string using this regex:

(?<!\\)[=~]  returns: ['\~foo\~\=bar ', 'cheese', 'monkey']   for '\~foo\~\=bar =cheese~monkey' returns: ['', 'foo\~\=bar ', 'cheese', 'monkey'] for '~foo\~\=bar =cheese~monkey'