Question

This works for ${VAR}:

Pattern.compile("\\$\\{(.+?)\\}"); 

But I am struggling to format it so that it also accepts $VAR to the next word boundry (\b). Because the text can be

$FIRSTVAR.${SECONDVAR}LITERAL

and then I want to detect both $FIRSTVAR and ${SECONDVAR} and if the first is “X” and the second if “Y”, I want to replace it to X.YLITERAL. The template uses both $VAR and ${VAR} styles, prefers the former if the var is followed with a non-word character but uses the latter if it is (just like in the example I gave above).

I tried

Pattern.compile("\\$(\\{|)(.+?)(\\}|\b})");

But that matches FIRSTVAR.${SECONDVAR as group(2). So it’s not good.
Thanks in advance

Answer 1

I would write:

Pattern.compile("\\$(?:(\\w+)|\\{(\\w+)\\})")

Naturally, this means that either matcher.group(1) or matcher.group(2) will be the variable-name — the other will be null — so you’ll have to check both.

Another, less-robust option is to write:

Pattern.compile("\\$\\{?(\\w+))\\}?")

but then it would replace e.g. $SECONDVAR} with Y rather than with Y}.

---

Edited to add: If you’re using Java 7, I think you should be able to write

Pattern.compile("\\$(?:(?<varname>\\w+)|\\{(?<varname>\\w+)\\})")

and then retrieve the variable-name using matcher.group("varname"). (I haven’t tested that in Java, because I only have Java 6 handy, and Java 6 doesn’t support named capture-groups. But it does work in Perl.) See “Group name” in the java.util.regex.Pattern javadoc and the javadoc for java.util.regex.Matcher.group(java.lang.String).