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• # Operations of character classes and use with quantifier

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Dear readers in previous blog I have explained about the character classes(basic definition). Now in this tutorial I am going to explain all of you about operations of character classes with Unions, Intersections, Subtractions and how we can use character classes with quantifiers.

Unions of character classes:

Single character class containing 2 or more character classes is called as Union of character classes . For creating a Union, we have to nest one character class inside the other character class.

Eg : [a-f[x-z]]. This union character class matches the letters a,b,c,d,e,f,x,y and z.

Enter the regex: [a-f[x-z]]

Enter input string to search: y

I found the letter "y" starting at index 0 and ending at index 1.

Enter the regex: [a-f[x-z]]

Enter input string to search: k

No match found.

Intersection of character classes:

Single character class containing 2 or more character classes inside one class with the use of && between 2 character classes, hence it is called as intersection of character classes . It will match the characters which are common to all character classes.

Eg: [a-z && [abc]]. This intersection character classes matches the letters only a,b and c.

Enter the regex: [a-z && [abc]]

Enter input string to search: c

I found the letter "c" starting at index 0 and ending at index 1.

Enter the regex: [a-z && [abc]]

Enter input string to search: f

No match found.

Enter the regex: [0-9 && [3-8]]

Enter input string to search: 5

I found the digit "5" starting at index 0 and ending at index 1.

Enter the regex:  [0-9 && [3-8]]

Enter input string to search: 2

No match found.

Subtraction of character classes:

Single character class containing 2 or more character classes inside one class with the use of && between 2 character classes and use of ^ in other nested character class, it is called as subtraction of character classes . It will match the characters except that characters which are available in other character class.

Eg: [a-z && [^abc]]. This subtraction character classes matches the letters except abc.

Enter the regex: [a-z && [^abc]]

Enter input string to search: t

I found the letter "t" starting at index 0 and ending at index 1.

Enter the regex: [a-z && [^abc]]

Enter input string to search: b

No match found.

Use of character classes and capturing groups with quantifier:

If regular expression is ‘xyz+’ means it will match x followed by y followed by z one or more times means we can attach a quantifier not only on a single character also attach on a character classes and capturing group such as [xyz]+ , it will match x or y or z one or more times and if regular expression is (xyz)+ , it will match the group (x followed by y followed by z) one or more times.

Eg:  Enter the regex: (sri){3}

Enter input string to search: srisrisrisrisrisri

I found the text “srisrisri” starting at index 0 and ending at index 9.

I found the text “srisrisri” starting at index 9 and ending at index 18.

Enter the regex: sri{3}

Enter input string to search: srisrisrisrisrisri

No match found.

In the first example quantifier applies to the entire capturing group sri means s followed by r followed by i 3 times, it will match to the input string, Hence the result will be true.

In the second example remove the parenthesis then regex will s followed by r followed i, here i is 3 times and it will match to the input string, Hence the result will be false.

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