Question

I’m trying to escape a RegExp metacharacter in Java. Below is what I want:

INPUT STRING: "This is $ test"
OUTPUT STRING: "This is \$ test"

This is what I’m currently doing but it’s not working:

String inputStr= "This is $ test";
inputStr = inputStr.replaceAll("$","\\$");

But I’m getting wrong output:

"This is $ test$"

Answer 1

You’ll need:

inputStr.replaceAll("\\$", "\\\\\\$");

The String to be replaced needs 2 backslashes because $ has a special meaning in the regexp. So $ must be escaped, to get: \$, and that backslash must itself be escaped within the java String: "\\$".

The replacement string needs 6 backslashes because both \ and $ have special meaning in the replacement strings:

• \ can be used to escape characters in the replacement string.
• $ can be used to make back-references in the replacement string.

So if your intended replacement string is “\$”, you need to escape each of those two characters to get: \\\$, and then each backslash you need to use – 3 of them, 1 literal and 2 for escapes – must also be escaped within the java String: "\\\\\\$".

See: Matcher.replaceAll