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Merge pull request #118 from webbertakken/patch-1

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Add more context to (non) capturing groups
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Zeeshan Ahmad 2018-04-16 21:13:10 +04:00 committed by GitHub
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@ -263,14 +263,14 @@ regular expression `[0-9]{3}` means: Match exactly 3 digits.
[Test the regular expression](https://regex101.com/r/Sivu30/1)
## 2.5 Character Group
## 2.5 Capturing Group
Character group is a group of sub-patterns that is written inside Parentheses `(...)`.
As we discussed before that in regular expression if we put a quantifier after a
character then it will repeat the preceding character. But if we put quantifier
after a character group then it repeats the whole character group. For example,
A capturing group is a group of sub-patterns that is written inside Parentheses
`(...)`. Like As we discussed before that in regular expression if we put a quantifier
after a character then it will repeat the preceding character. But if we put quantifier
after a capturing group then it repeats the whole capturing group. For example,
the regular expression `(ab)*` matches zero or more repetitions of the character
"ab". We can also use the alternation `|` meta character inside character group.
"ab". We can also use the alternation `|` meta character inside capturing group.
For example, the regular expression `(c|g|p)ar` means: lowercase character `c`,
`g` or `p`, followed by character `a`, followed by character `r`.
@ -280,6 +280,27 @@ For example, the regular expression `(c|g|p)ar` means: lowercase character `c`,
[Test the regular expression](https://regex101.com/r/tUxrBG/1)
Note that capturing groups do not only match but also capture the characters for use in
the parent language. The parent language could be python or javascript or virtually any
language that implements regular expressions in a function definition.
### 2.5.1 Non-capturing group
A non-capturing group is a capturing group that only matches the characters, but
does not capture the group. A non-capturing group is denoted by a `?` followed by a `:`
within parenthesis `(...)`. For example, the regular expression `(?:c|g|p)ar` is similar to
`(c|g|p)ar` in that it matches the same characters but will not create a capture group.
<pre>
"(?:c|g|p)ar" => The <a href="#learn-regex"><strong>car</strong></a> is <a href="#learn-regex"><strong>par</strong></a>ked in the <a href="#learn-regex"><strong>gar</strong></a>age.
</pre>
[Test the regular expression](https://regex101.com/r/Rm7Me8/1)
Non-capturing groups can come in handy when used in find-and-replace functionality or
when mixed with capturing groups to keep the overview when producing any other kind of output.
See also [4. Lookaround](# 4. Lookaround).
## 2.6 Alternation
In regular expression Vertical bar `|` is used to define alternation.