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Character classes

Character classes are groups of characters to test for. By enclosing characters inside of square brackets,

you are effectively telling the regular expression to match the first character, the second character, the

third character, or so on. For example, to match the characters a, b, and c, the character class is

[abc]

This is called a

simple class

, because it specifies the exact characters to look for.

Simple classes

Suppose you want to match

“bat”

“cat”

, and

“fat”

. It is very easy to use a simple character class for

this purpose:

var sToMatch = “a bat, a Cat, a fAt baT, a faT cat”;

var reBatCatRat = /[bcf]at/gi;

var arrMatches = sToMatch.match(reBatCatRat);

The

arrMatches

array is now be filled with these values:

“bat”

“Cat”

“fAt”

“baT”

“faT”

, and

“cat”.

You can also include special characters inside simple classes (and any other type of character

class as well). Suppose you replace the

character with its Unicode equivalent:

var sToMatch = “a bat, a Cat, a fAt baT, a faT cat”;

var reBatCatRat = /[\u0062cf]at/gi;

var arrMatches = sToMatch.match(reBatCatRat);

This code behaves the same as it did in the previous example.

Negation classes

At times you may want to match all characters except for a select few. In this case, you can use a

negation

class

, which specifies characters to exclude. For example, to match all characters except

and

, the charac-

ter class is

[^ab]

. The caret (

) tells the regular expression that the character must not match the characters

to follow.

Going back to the previous example, what if you only wanted to get words containing

but not begin-

ning with

var sToMatch = “a bat, a Cat, a fAt baT, a faT cat”;

var reBatCatRat = /[^bc]at/gi;

var arrMatches = sToMatch.match(reBatCatRat);

In this case,

arrMatches

contains

“fAt”

and

“faT”

, because these strings match the pattern of a

sequence ending with

but not beginning with

Range classes

Up until this point, the character classes required you to type all the characters to include or exclude.

Suppose that you want to match any alphabet character, but you really don’t want to type every letter

in the alphabet. Instead, you can use a

range class

to specify a range between

and

[a-z]

. The key

here is the dash (

), which should be read as

through

instead of

minus

(so the class is read as

a through z

not

a minus z

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Regular Expressions

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