scala regex: extract expression from string

Question

I'd like to extract the expressions ${*} from a String.

val example = "Hello ${foo.bar} World"

But the dollar sign and the curly brackets are part of the expression syntax, so I tried to escape it.

val expr = "\\$\\{[a-zA-Z0-9\\w]*\\}".r

But this won't work and println prints nothing:

for (ex <- expr.findAllMatchIn(example)) println(ex)

Anyone has an idea what's wrong? There exists a more elegant regex?

sshashank124 · Accepted Answer · 2014-04-25 09:35:58Z

2

That is because you are not accounting for the . in foo.bar, do this instead:

\\$\\{[a-zA-Z0-9.\\w]*\\}             // allows for a . to also be in the string

For maximum flexibility, you can do:

\\$\\{[^}]*.

answered Apr 25, 2014 at 9:35

sshashank124

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3 Comments

Themerius Over a year ago

Thank you, """\$\{[^}]*.""".r works very well, it is also possible to extract multiple expressions. val example2 = "hello ${foo.bar} world ${bar.foo}". Therefore I accept this answer. :)

som-snytt Over a year ago

Definitely got to rock the triple quotes, though. It makes it easier to spot mistakes.

Andreas Neumann Over a year ago

You should definitly put more emphasis on the shortcommings of the first solution. It will only work if there are no repetitions of "}" . The second one would be the only safe way to go.

DNA · Accepted Answer · 2014-04-25 09:45:57Z

2

You can use a simpler regex, and you can make it easier to read (avoiding the need for double escaping \\) by using triple-quotes:

val example = "Hello ${foo.bar} World ${bar.foo}"
                                              //> example  : String = Hello ${foo.bar} World ${bar.foo}

val expr = """\$\{.*?\}""".r                    //> expr  : scala.util.matching.Regex = \$\{.*?\}

for (ex <- expr.findAllMatchIn(example)) println(ex)
                                              //> ${foo.bar}
                                              //| ${bar.foo}

edited Apr 25, 2014 at 9:45

answered Apr 25, 2014 at 9:37

DNA

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2 Comments

Themerius Over a year ago

Thank you! """\$\{.*\}""".r works very well, but if multiple expressions occour, it matches to much. For example val example2 = "hello ${foo.bar} world ${bar.foo}".

DNA Over a year ago

Fixed - I have added a non-greedy modifier (?)

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