Fix hang if non-existing label is searched.

README

@@ -24,6 +24,8 @@ The solution is to allow the web server user to execute a single command as anot
 * the command-line interface, that is run on the server by a user with read access to the documents;
 * the web interface, that is run on the web server, with no access to the documents save through the CLI interface.
 
+Finally, all the input (search terms, etc.) is verified by the CLI script, so that any number of frontends can be written and benefit from the same strict controls.
+
 = INSTALLATION AND DEPENDENCIES =
 
 The script may be copied anywhere. Its dependencies are standard, although I only tested on Debian: bash, find, gawk, sed, grep, file, ls.

cli/paperfind.sh

@@ -102,7 +102,7 @@ Q)
   if [ ${#labels[*]} -gt 0 ]; then
     # This is an AND
     for l in "${labels[@]}"; do
-      found="$(
+      [ -n "$found" ] && found="$(
         eval grep -lF${q_ci:+i}e "$l" ${found//|/labels} 2>/dev/null \
         | sed 's#labels$#|#')"
     done
@@ -111,7 +111,7 @@ Q)
     #  eval grep -lF${q_ci:+i}f <(printf '%s\n' "${labels[@]}") ${found//|/labels} 2>/dev/null \
     #  | sed 's#labels$#|#')"
   fi
-  if [ ${#words[*]} -gt 0 ]; then
+  if [ ${#words[*]} -gt 0 ] && [ -n "$found" ]; then
     # This is an AND
     tmpf="$(
       eval grep -Ho "'>[^<>]*</span'" ${found//|/paper.*.words} 2>/dev/null \