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Let's say I have the line below:
one two three
Is it possible to write a regex that would return below?
one three
I can of course get each part in a separate group but is it possible to capture that in a single match?
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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" .
A Match is an object that indicates a particular regular expression matched (a portion of) the target text. A Group indicates a portion of a match, if the original regular expression contained group markers (basically a pattern in parentheses).
Parentheses group the regex between them. They capture the text matched by the regex inside them into a numbered group that can be reused with a numbered backreference. They allow you to apply regex operators to the entire grouped regex. (abc){3} matches abcabcabc.
To match a character having special meaning in regex, you need to use a escape sequence prefix with a backslash ( \ ). E.g., \. matches "." ; regex \+ matches "+" ; and regex \( matches "(" . You also need to use regex \\ to match "\" (back-slash).
To put it simply: no, it can't be done (as discussed in comments on your original question).
To find out why, let's look at it a bit more generally. A regular expression can be modelled as a (often complex) deterministic finite automaton, also known as a DFA, and your average regex engine is implemented as one. What this means is that the regex will slurp zero or one character at a time, and see if it matches the current token. If not, it will backtrack and attempt to match any possible token at the current stage (done with the alternation operation |). If unable, it halts and reports it cannot match. Since a DFA operates on the input in sequential order, what you're asking for is basically impossible by definition.
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