Groovy regex PatternSyntaxException when parsing GString-style variables -

groovy here. i'm being given string gstring-style variables in like:

string target = 'how brown ${animal}. ${role} has oddly-shaped ${bodypart}.' 

keep in mind, not intended used actual gstring!!! is, i'm not going have 3 string variables (animal, role , bodypart, respectively) groovy resolving @ runtime. instead, i'm looking 2 distinct things these "target" strings:

• i want able find instances of these variables refs ("${*}") in target string, , replace ?; and
• i need find instances of these variables refs , obtain list (allowing dupes) names (which in above example, [animal,role,bodypart])

my best attempt far:

class targetstringutils {     private static final string variable_pattern = "\${*}"      // example input: 'how brown ${animal}. ${role} has oddly-shaped ${bodypart}.'     // example desired output: 'how brown ?. ? has oddly-shaped ?.'     static string replacevarswithquestionmarks(string target) {         target.replaceall(variable_pattern, '?')     }      // example input: 'how brown ${animal}. ${role} has oddly-shaped ${bodypart}.'     // example desired output: [animal,role,bodypart]    } list of strings       static list<string> collectvariablerefs(string target) {         target.findall(variable_pattern)     } } 

...produces patternsytaxexception anytime go run either method:

exception in thread "main" java.util.regex.patternsyntaxexception: illegal repetition near index 0 ${*} ^ 

any ideas i'm going awry?

the issue have not escaped pattern properly, , findall collect matches, while need capture subpattern inside {}.

use

def target = 'how brown ${animal}. ${role} has oddly-shaped ${bodypart}.' println target.replaceall(/\$\{([^{}]*)\}/, '?') // => how brown ?. ? has oddly-shaped ?.  def lst = new arraylist<>(); def m = target =~ /\$\{([^{}]*)\}/ (0..<m.count).each { lst.add(m[it][1]) } println lst   // => [animal, role, bodypart] 

see this groovy demo

inside /\$\{([^{}]*)\}/ slashy string, can use single backslashes escape special regex metacharacters, , whole regex pattern looks cleaner.

• \$ - match literal $
• \{ - match literal {
• ([^{}]*) - group 1 capturing characters other { , }, 0 or more times
• \} - literal }.