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Table of Contents

14.2. REGEX Special characters in Regex

There are various special characters in regex which are listed as follows:

Special Characters

SN symbol Description
1 . Matches any character except newline character
2 ^ Matches starting of the string
3 $ Matches end of the string
4 * Matches 0 or more occurrences
5 + Matches 1 or more occurrences
6 ? Matches 0 ir 1 occurrences
7 {m} Matches exactly m number of occurrences
8 {m,n} Matches m to n occurrences
9 {m,n}? Tries to match as few occurrences as possible but with in range {m,n}
10 *?, +?, ?? Tries to match as few occurrences qualified by *, +, and ?
11 \ Escapes the regular character or special character
12 [] Matches any character that is written within the brackets
13 A|B Matches A or B
14 (...) Matches whatever regular expression is inside parenthesis

Escape Sequences in a regular expression

Regular expression escape sequences not only escapes regular characters but special characters too. for example if we want to include a character * in regular expression, it has it's own meaning which means it needs to be escaped. by writing \*

SN Symbol Description
1 \A Matches only at the start of the string
2 \b Matches the empty string but only ar the beginning or the end of the string.
3 B Matches the empty string but only when it is not at the beginning or the end of a word
4 \d Matches a number from 0-9
5 \D Matches a character except a number from 0-9
6 \s Matches white space character such as space or tab
7 \S Matches a character except white space characters
8 \w Matches a character that contains alphanumeric character or _ character
9 \W Matches any character except alphanumeric or _ character
10 \Z Matches only at the end of the string

Set of characters in regex

A set of characters in regex are denoted inside a pair of square brackets []. Unlike special characters in regular regex, special characters (such as *, +, etc) inside large brackets has no meaning.

some of the regex set matches are as follows:

SN Symbol Description
1 [abc] matches either of a, b or c.
2 [a-m] matches either of character from a to m
3 [a-m0-5] matches either of character from a to m followed by number from 0 to 5
4 [0-9A-Fa-f] matches any hexadecimal character from 0-9 and a-f or A-F
5 [^abc] matches either of character except abc
6 [0123] matches either of 0, 1, 2, or 3
7 [ab][12] matches either of a1, a2, b1, or b2
8 [+*] matches either of + or * characters (but no matches for number of occurrences)

We can also find the number of occurrences of set of characters by specifying *, + or ? after brackets.

For Example:

  • [0-9A-Fa-f]+ matches any number of occurrences that matches [0-9A-Fa-f]. Example: 0, 1, 1A, ff0c, etc.
  • [\d]{4} matches exactly 4 numeric characters from the string.