diff --git a/R/Utils.R b/R/Utils.R
index 699468a059247a6a9f2b0c11e5d75ccaddcedf7a..8626b2a015b3e5fe90fb9c3af697b7ed7595c5b0 100644
--- a/R/Utils.R
+++ b/R/Utils.R
@@ -277,6 +277,9 @@ chunk <- function(chunk, n_chunks, selectors) {
 }
 
 .FindTagValue <- function(path_with_globs_and_tag, actual_path, tag) {
+
+  addition_warning = FALSE
+
   if (!all(sapply(c(path_with_globs_and_tag, actual_path, tag), is.character))) {
     stop("All 'path_with_globs_and_tag', 'actual_path' and 'tag' must be character strings.")
   }
@@ -308,34 +311,90 @@ chunk <- function(chunk, n_chunks, selectors) {
   clp <- chosen_left_part <- which.min(group_len_diffs)[1]
 
   left_expr <- paste(parts[1:clp], collapse = full_tag)
+
+  #because ? means sth, use . (any char) to substitute ?
   left_expr <- gsub('?', '.', left_expr, fixed = TRUE)
-  # The .*? will force lazy evaluation (find the shortest match from the 
-  # beginning of the actual_path).
+  test_left_expr <- left_expr
+
+  # because * means zero or more char, use . to substitute *. 
+  # And the * behind . means zero or more char. '?' for lazy evaluation.
   left_expr <- gsub('*', '.*?', left_expr, fixed = TRUE)
   left_expr <- gsub(full_tag, '.*?', left_expr, fixed = TRUE)
+
+  # To test if the pattern matches only one... dont use lazy evaluation
+  test_left_expr <- gsub('*', '.*', test_left_expr, fixed = TRUE)
+  test_left_expr <- gsub(full_tag, '.*', test_left_expr, fixed = TRUE)
+
+  # Find the match chars from left
   left_match <- regexec(left_expr, actual_path)[[1]]
+  test_left_match <- regexec(test_left_expr, actual_path)[[1]]
+
   if (left_match < 0) {
     stop("Unexpected error in .FindTagValue.")
   }
 
+  if (attr(test_left_match, "match.length") != attr(left_match, "match.length")) {
+    addition_warning = TRUE
+    warning("Detect more than one possibility derived from the global expression of path.")
+  }
+
+  #Cut down the left match part
+  actual_path_sub <- substr(actual_path, 
+                            attr(left_match, 'match.length') + 1, 
+                            nchar(actual_path))
+
+  #----------Search match chars from right
   right_expr <- paste(parts[(clp + 1):(length(parts))], collapse = full_tag)
   right_expr <- gsub('?', '.', right_expr, fixed = TRUE)
+
+  test_right_expr <- right_expr
   # For lazy evaulation to work, pattern and string have to be reversed.
   right_expr <- gsub('*', '.*?', right_expr, fixed = TRUE)
   right_expr <- gsub(full_tag, '.*?', right_expr, fixed = TRUE)
   right_expr <- gsub('$', '^', right_expr, fixed = TRUE)
+
+  # To test if the pattern matches only one... dont use lazy evaluation
+  test_right_expr <- gsub('*', '.*', test_right_expr, fixed = TRUE)
+  test_right_expr <- gsub(full_tag, '.*', test_right_expr, fixed = TRUE)
+  test_right_expr <- gsub('$', '^', test_right_expr, fixed = TRUE)
+
   rev_str <- function(s) {
     paste(rev(strsplit(s, NULL)[[1]]), collapse = '')
   }
+
   right_expr <- rev_str(right_expr)
+  test_right_expr <- rev_str(test_right_expr)
+
   right_expr <- gsub('?*.', '.*?', right_expr, fixed = TRUE)
   right_match <- regexec(right_expr, rev_str(actual_path))[[1]]
+
+  test_right_expr <- gsub('*.', '.*', test_right_expr, fixed = TRUE)
+  test_right_match <- regexec(test_right_expr, rev_str(actual_path_sub))[[1]]
+
   if (right_match < 0) {
     stop("Unexpected error in .FindTagValue.")
   }
+
+  if (attr(test_right_match, "match.length") != attr(right_match, "match.length")) {
+    addition_warning = TRUE
+    warning(paste0("Detect more than one possibility derived from the global ",
+                   "expression of path."))
+  }
+
+  #-------------get tag value
   right_match[] <- nchar(actual_path) - 
                    (right_match[] + attr(right_match, 'match.length') - 1) + 1
 
+  if (addition_warning) {
+    warning(paste0("The extracted parameter ", full_tag, " is ",
+                   substr(actual_path, left_match + attr(left_match, 'match.length'), 
+                   right_match - 1),
+                   ". Check if all the desired files were read in. ",
+                   "If not, specify parameter '", tag, 
+                   "' by values instead of indices, or set parameter ",
+                   "'path_glob_permissive' as TRUE"))
+  }
+
   if ((left_match + attr(left_match, 'match.length')) > 
       (right_match - 1)) {
     NULL