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is it possible to specify non-capturing groups in sed?
if so, how?
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Grouping can be used in sed like normal regular expression. A group is opened with “\(” and closed with “\)”. Grouping can be used in combination with back-referencing. Back-reference is the re-use of a part of a Regular Expression selected by grouping.
tl;dr non-capturing groups, as the name suggests are the parts of the regex that you do not want to be included in the match and ?: is a way to define a group as being non-capturing. Let's say you have an email address [email protected] . The following regex will create two groups, the id part and @example.com part.
Capturing groups are a way to treat multiple characters as a single unit. They are created by placing the characters to be grouped inside a set of parentheses. For example, the regular expression (dog) creates a single group containing the letters "d" "o" and "g" .
Mixing named and numbered capturing groups is not recommended because flavors are inconsistent in how the groups are numbered. If a group doesn't need to have a name, make it non-capturing using the (?:group) syntax. In . NET you can make all unnamed groups non-capturing by setting RegexOptions.
Parentheses can be used for grouping alternatives. For example:
sed 's/a\(bc\|de\)f/X/' says to replace "abcf" or "adef" with "X", but the parentheses also capture. There is not a facility in sed to do such grouping without also capturing. If you have a complex regex that does both alternative grouping and capturing, you will simply have to be careful in selecting the correct capture group in your replacement.
Perhaps you could say more about what it is you're trying to accomplish (what your need for non-capturing groups is) and why you want to avoid capture groups.
Edit:
There is a type of non-capturing brackets ((?:pattern)) that are part of Perl-Compatible Regular Expressions (PCRE). They are not supported in sed (but are when using grep -P).
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