add a 'Upper' expr helper (#50)

* add a 'Upper' expr helper

* remove redundant startsWith and endsWith

pkg/exprhelpers/exprlib.go

@@ -24,23 +24,18 @@ func Atof(x string) float64 {
 	return ret
 }
 
-func StartsWith(s string, pref string) bool {
-	return strings.HasPrefix(s, pref)
-}
-
-func EndsWith(s string, suff string) bool {
-	return strings.HasSuffix(s, suff)
+func Upper(s string) string {
+	return strings.ToUpper(s)
 }
 
 func GetExprEnv(ctx map[string]interface{}) map[string]interface{} {
 	var ExprLib = map[string]interface{}{
-		"Atof": Atof,
-		"StartsWith": StartsWith,
-		"EndsWith" : EndsWith,
-		"JsonExtract": JsonExtract,
+		"Atof":           Atof,
+		"JsonExtract":    JsonExtract,
 		"JsonExtractLib": JsonExtractLib,
-		"File": File,
-		"RegexpInFile": RegexpInFile,
+		"File":           File,
+		"RegexpInFile":   RegexpInFile,
+		"Upper":          Upper,
 	}
 	for k, v := range ctx {
 		ExprLib[k] = v