Extract variables from string with Regex

Question

I'm trying to extract from a string variables with the following format: ${var}

Given this string:

val s = "This is a string with ${var1} and ${var2} and {var3}"

The result should be

List("var1","var2")

This is the attempt, it ends in an exception. What's wrong with this regex?

val pattern = """\${([^\s}]+)(?=})""".r
val s = "This is a string with ${var1} and ${var2} and {var3}"
val vals = pattern.findAllIn(s)

println(vals.toList)

and the exception:

Exception in thread "main" java.util.regex.PatternSyntaxException:

Illegal repetition near index 1 \${([^\s}]+)(?=})

Your code has the regex as \${([^\s}]+)(?=}) but the error shows /${([^/s}]+)(?=}) - both the slashes are different, shows forward / in the error. — aneroid
– aneroid, Commented Jun 26, 2016 at 3:42

rock321987 · Accepted Answer · 2016-06-26 04:02:42Z

5

NOTE :- { in regex have special meaning. It denotes range. e.g. a{2,10} denotes match a in between 2 to 10 times. So you need to escape {.

Solution 1

val pattern = """\$\{([^\s}]+)(?=})""".r

You need to access the first capturing group for finding the result and then change it to list.

Solution 2

You can also use lookbehind like

val pattern = """(?<=\$\{)[^\s}]+(?=})""".r

Ideone Demo

edited Jun 26, 2016 at 4:02

answered Jun 26, 2016 at 3:45

rock321987

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