Java replaceAll

Question

I was using String.replaceAll(String, String) when I noticed that replacing a string with $ symbols around it would not work. Example $REPLACEME$ would not be replaced in a Linux system. Anyone know why this is?

Some code:

String foo = "Some string with $REPLACEME$";
foo = foo.replaceAll("$REPLACEME$", "characters");
System.out.println(foo);

Output:

Some string with $REPLACEME$

• Jon Skeet: Why are you using replaceAll rather than replace? Do you need regular expressions?

Answer 1

$ is a special character that needs to be escaped:

foo = foo.replaceAll("\\$REPLACEME\\$", "characters");

Or more generally use Pattern.quote which will escape all metacharacters (special characters like $ and ?) into string literals:

foo = foo.replaceAll(Pattern.quote("$REPLACEME$"), "characters");

• TameHog: Why does it need to be escaped?
• Maarten Bodewes: It means end of a line in regular expression syntax. So unless you have an end of string at the start of your string...
• Maarten Bodewes: +1 for Pattern.quote, I was already contemplating an answer.
• TameHog: Thanks for the Pattern.quote

Answer 2

replaceAll uses a regular expression as its first argument. $ is an anchor character that matches the end of a matching string in regex so needs to be escaped

foo = foo.replaceAll("\\$REPLACEME\\$", "characters");

• Gary: I would also add that in pure regex, a literal dollar sign has to be escaped \$, but in Java the escape character has to be escaped, hence \\$.

Answer 3

The replaceAll method uses regular expressions, and the $ character is a metacharacter in a regular expression that represents the end of the string. However, the replace method also replaces all instances of the target string with the replacement string, and uses an ordinary string, not a regular expression. This will do what you are expecting:

String foo = "Some string with $REPLACEME$";
foo = foo.replace("$REPLACEME$", "characters");
System.out.println(foo);