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Add alternation

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Zeeshan Ahmed 2017-07-24 09:12:30 +01:00
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@ -29,6 +29,7 @@ contains uppercase letter and also it is too short.
- [The Plus]()
- [The Question Mark]()
- [Character Group]()
- [Alternation]()
- [Quantifiers]()
- [OR operator]()
- [Character Sets]()
@ -184,9 +185,21 @@ the comma the regular expression `[0-9]{2}` means: Match exactly 2 digits.
Character group is a group of sub-pattern that is written inside Parentheses `(...)`. As we discussed before that in regular expression
if we put quantifier after character than it will repeats the preceding character. But if we put quantifier after a character group than
it repeats the whole character group. For example the regular expression `(ab)*` matches zero or more repetitions of the character "ab".
We can also use the alternation inside character group. For example the regular expression `(c|g|p)ar` means: lowercase character `c`,
We can also use the alternation `|` meta character inside character 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`.
<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>
## 2.5 Alternation
In regular expression Vertical bar `|` is used to define alternation. Alternation is like a condition between multiple expressions. Now,
you maybe thinking that character set and alternation works the same way. But the big difference between character set and alternation
is that character set works on character level but alternation works on expression level. For example the regular expression
`[T|t]he|car` means: uppercase character `T` or lowercase `t`, followed by lowercase character `h`, followed by lowercase character `e`
or lowercase character `c`, followed by lowercase character `a`, followed by lowercase character `r`.
<pre>
"[T|t]he|car" => <a href="#learn-regex"><strong>The</strong></a> <a href="#learn-regex"><strong>car</strong></a> is parked in <a href="#learn-regex"><strong>the</strong></a> garage.
</pre>