RegEx基于组的不同替换？

Question

So I'm relatively n00bish at regular expressions, and doing a little practicing.

I'm playing with a dog-simple "deobfucator" that just looks for [dot] or (dot) or [at] or (at) . Case-insensitive, and with or w/out any number of spaces before or after the match(s).

This is for the usual: someemail [AT] domain (dot) com type of thing. I want to obviously turn it into someemail@domain.com .

The RegEx I've come up with does the matching fine, but now I want to replace with either a . or a @ depending on the match.

ie I want the group matching the "dot" group to replace it with the literal . , and the group matching the "at" group with the literal @ .

I know I could just write 2 different (almost identical) RegEx's and run it through both, but for the sake of education, I'm trying to see if I can do it all in one RegEx?

Here's the RegEx I came up with (probably not the smallest possible, which I'd also be interested in seeing):

+(\\[|\\()(dot)(\\)|\\]) +| +(\\[|\\()(at)(\\)|\\]) +

NOTE: before each + there's an empty space, for matching spaces.

What I'm looking for is what I would use to do the replacement(s) properly?

Update: Sorry all, forgot to add which language I was working with for this. In this case, I'm using a clipboard utility that can run RegEx's on it's input (whatever gets copied to the clipboard), and the engine it uses is C#/VB.NET . Ultimate goal for this little project is to just be able to copy an "obfuscated" email address or URL, and run the RegEx on it so that it's set on the clipboard in it's "unobfuscated" state.

That said, I do tend to use RegEx's on many different languages, so converting them between languages generally isn't an issue.

Answer 1

.NET regex does not support conditional replacement patterns.

for the sake of education, I'm trying to see if I can do it all in one RegEx?

There are other regex engines that allow conditional replacement logic in a single regex replacement operation with conditional replacement patterns .

There are 3 engines that support this type of replacements: JGsoft V2, Boost, and PCRE2.

For conditionals to work in Boost, you need to pass regex_constants::format_all to regex_replace . For them to work in PCRE2, you need to pass PCRE2_SUBSTITUTE_EXTENDED to pcre2_substitute .

In PCRE2:

${1:+matched:unmatched} where 1 is a number between 1 and 99 referencing a numbered capturing group. If your regex contains named capturing groups then you can reference them in a conditional by their name: ${name:+matched:unmatched} .

If you want a literal colon in the matched part, then you need to escape it with a backslash. If you want a literal closing curly brace anywhere in the conditional, then you need to escape that with a backslash too. Plus signs have no special meaning beyond the :+ that starts the conditional, so they don't need to be escaped.

Also, see The Boost-Specific Format Sequences :

When specifying the format_all flag to regex_replace() , the escape sequences recognized are the same as those above for format_perl . In addition, conditional expressions of the following form are recognized:

?Ntrue-expression:false-expression

where N is a decimal digit representing a sub-match. If the corresponding sub-match participated in the full match, then the substitution is true-expression. Otherwise, it is false-expression. In this mode, you can use parens () for grouping. If you want a literal paren, you must escape it as \\( .

In Boost replacement patterns, literal ( and ) must be escaped.

The syntax for JGsoft V2 replacement string conditionals is the same as that in the C++ Boost library.

So, your regex can be contracted to ( +)[[(](?:(dot)|(at))[])]( +) :

• ( +) - Group 1: one or more spaces
• [[(] - a [ or (
• (?:(dot)|(at)) - Either (Group 2) a dot substring or (Group 3) an at substring
• [])] - a ) or ]
• ( +) - Group 4: one or more spaces

And replace with $1(?{3}.:@)$4 :

• $1 - Group 1 value,
• (?{3}.:@) - if Group 3 matched, replace with . , else with @
• $4 - Group 4 value.

This is available in Notepad++:

Answer 2

If you are using Java, try replaceAll method from String class.

And finally you need to normalize it with white spaces:
- Pure Java - String after = before.trim().replaceAll("\\\\s+", " ");
- Pure Java - String after = before.replaceAll("\\\\s{2,}", " ").trim();
- Apache commons lang3 - String after = StringUtils.normalizeSpace(String str);
- ...