add argument presence check for functions in dirs plugin to bad usage

plugins/available/dirs.plugin.bash

@@ -67,7 +67,8 @@ fi
 
 alias L='cat ~/.dirs'
 
-G () {				# goes to distination dir otherwise , stay in the dir
+# goes to distination dir otherwise, stay in the dir
+G () {
     about 'goes to destination dir'
     param '1: directory'
     example '$ G ..'
@@ -76,20 +77,28 @@ G () {				# goes to distination dir otherwise , stay in the dir
     cd "${1:-$(pwd)}" ;
 }
 
-S () {				# SAVE a BOOKMARK
+S () {
     about 'save a bookmark'
+    param '1: bookmark name'
+    example '$ S mybkmrk'
     group 'dirs'
 
+    [[ $# -eq 1 ]] || { echo "${FUNCNAME[0]} function requires 1 argument"; return 1; }
+
     sed "/$@/d" ~/.dirs > ~/.dirs1;
     \mv ~/.dirs1 ~/.dirs;
     echo "$@"=\"`pwd`\" >> ~/.dirs;
     source ~/.dirs ;
 }
 
-R () {				# remove a BOOKMARK
+R () {
     about 'remove a bookmark'
+    param '1: bookmark name'
+    example '$ R mybkmrk'
     group 'dirs'
 
+    [[ $# -eq 1 ]] || { echo "${FUNCNAME[0]} function requires 1 argument"; return 1; }
+
     sed "/$@/d" ~/.dirs > ~/.dirs1;
     \mv ~/.dirs1 ~/.dirs;
 }