Question

I want to create a regular expression for strings which uses special characters [ and ].

Value is "[action]".

Expression I am using is "[\[[\x00-\x7F]+\]]".

I tried doing it by adding \ before [ and ].

But it doesn t work.

Can any one help me with this.

Answer 1

You probably want to remove the enclosing brackets "[]". In regexps they mean a choice of one of the enclosed characters

Answer 2

Two backslashes before the open and close brackets: \[ and \]

The double backslash evaluates a single backslash in the string. The single backslash escapes the brackets so that they are not interpreted as surrounding a character class.

No backslashes for the brackets that do declare the character class: [a-z] (you can you any range you like, not just a to z)

The Kleene star operator matches any number of characters in the range.

public class Regexp {
    public static void main(final String... args) {
        System.out.println("[action]".matches("\[[a-z]*\]"));
    }
}

On my system:

$ javac Regexp.java && java Regexp
true

Answer 3

Just stick one backslash before the square bracket.

Two backslashes escapes itself, so the regex engine sees [, where [ is a special char.

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