Brackets
Brackets ([]) have a special meaning when used in the context of regular expressions. They are used to find a range of characters.
Sr.No
| Expression & Description
|
1
| [0-9]
It matches any decimal digit from 0 through 9.
|
2
| [a-z]
It matches any character from lower-case a through lowercase z.
|
3
| [A-Z]
It matches any character from uppercase A through uppercase Z.
|
4
| [a-Z]
It matches any character from lowercase a through uppercase Z.
|
The ranges shown above are general; you could also use the range [0-3] to match any decimal digit ranging from 0 through 3, or the range [b-v] to match any lowercase character ranging from b through v.
Quantifiers
The frequency or position of bracketed character sequences and single characters can be denoted by a special character. Each special character having a specific connotation. The +, *, ?, {int. range}, and $ flags all follow a character sequence.
Sr.No
| Expression & Description
|
1
| p+
It matches any string containing at least one p.
|
2
| p*
It matches any string containing zero or more p's.
|
3
| p?
It matches any string containing zero or one p's.
|
4
| p{N}
It matches any string containing a sequence of N p's
|
5
| p{2,3}
It matches any string containing a sequence of two or three p's.
|
6
| p{2, }
It matches any string containing a sequence of at least two p's.
|
7
| p$
It matches any string with p at the end of it.
|
8
| ^p
It matches any string with p at the beginning of it.
|
Examples
Following examples will clear your concepts about matching characters.
Sr.No
| Expression & Description
|
1
| [^a-zA-Z]
It matches any string not containing any of the characters ranging from a through z and A through Z.
|
2
| p.p
It matches any string containing p, followed by any character, in turn followed by another p.
|
3
| ^.{2}$
It matches any string containing exactly two characters.
|
4
| <b>(.*)</b>
It matches any string enclosed within <b> and </b>.
|
5
| p(hp)*
It matches any string containing a p followed by zero or more instances of the sequence php.
|
