gistfile1.txt

import org.apache.commons.io.FileUtils

def json = FileUtils.readFileToString(new File("assets.json"))

def matcher = json =~ /\{ ".oid" : ("[0-9a-f]{24}") \}/

def stringBuffer = new StringBuffer();

matcher.reset()

while (matcher.find()) {
    matcher.appendReplacement(stringBuffer, matcher.group(1));
}

matcher.appendTail(stringBuffer);

println stringBuffer.toString()