Add grep method

common/src/main/java/ctbrec/StringUtil.java

@@ -1,6 +1,8 @@
 package ctbrec;
 
 import java.text.DecimalFormat;
+import java.util.StringTokenizer;
+import java.util.regex.Pattern;
 
 public class StringUtil {
     private StringUtil() {}
@@ -70,4 +72,17 @@ public class StringUtil {
                 .replace('\'', '_')
                 .replace('"', '_');
     } // @formatter:on
+
+    public static String grep(String input, String regex) {
+        StringTokenizer st = new StringTokenizer(input, "\n");
+        StringBuilder result = new StringBuilder();
+        Pattern p = Pattern.compile(regex);
+        while (st.hasMoreTokens()) {
+            String line = st.nextToken();
+            if (p.matcher(line).find()) {
+                result.append(line).append('\n');
+            }
+        }
+        return result.deleteCharAt(result.length() - 1).toString();
+    }
 }