Introduce nvm use --print-paths

It will print all paths that have been changed by nvm use. These paths are exported for all later nvm commands and need to be applied to the environment of other shells (in this case fish), therefore they are printed with the option.

nvm.sh

@@ -535,7 +535,7 @@ nvm() {
       echo "    nvm --version                        Print out the latest released version of nvm"
       echo "    nvm install [-s] <version>           Download and install a <version>, [-s] from source. Uses .nvmrc if available"
       echo "    nvm uninstall <version>              Uninstall a version"
-      echo "    nvm use <version>           Modify PATH to use <version>. Uses .nvmrc if available"
+      echo "    nvm [--print-paths] use <version>    Modify PATH (and optionally print it) to use <version>. Uses .nvmrc if available"
       echo "    nvm run <version> [<args>]           Run <version> with <args> as arguments. Uses .nvmrc if available for <version>"
       echo "    nvm current                          Display currently activated version"
       echo "    nvm ls                               List installed versions"
@@ -794,20 +794,35 @@ nvm() {
       fi
     ;;
     "use" )
+      shift # start treating the args given to "use"
+
       if [ $# -eq 0 ]; then
-        nvm help
-        return 127
-      fi
-      if [ $# -eq 1 ]; then
         nvm_rc_version
         if [ -n "$NVM_RC_VERSION" ]; then
           VERSION=`nvm_version $NVM_RC_VERSION`
         fi
-      elif [ "_$2" != '_system' ]; then
-        VERSION="$(nvm_version "$2")"
       else
-        VERSION="$2"
+        # Handle options
+        while [[ $# > 0 ]]; do
+                key="$1"
+                shift
+          case $key in 
+                  --print-paths)
+              PRINT_PATHS=true
+            ;;
+
+                  *)
+              if [ "_$key" != '_system' ]; then
+                      VERSION="$(nvm_version "$key")"
+                    else
+                      VERSION="$key"
                     fi
+              break
+            ;;
+          esac
+        done
+      fi
+
       if [ -z "$VERSION" ]; then
         nvm help
         return 127
@@ -822,7 +837,7 @@ nvm() {
           return 127
         fi
       elif [ "_$VERSION" = "_∞" ]; then
-        echo "The alias \"$2\" leads to an infinite loop. Aborting." >&2
+        echo "The alias \"$1\" leads to an infinite loop. Aborting." >&2
         return 8
       fi
 
@@ -858,6 +873,12 @@ nvm() {
       if [ "$NVM_SYMLINK_CURRENT" = true ]; then
         rm -f "$NVM_DIR/current" && ln -s "$NVM_VERSION_DIR" "$NVM_DIR/current"
       fi
+      if [ $PRINT_PATHS ]; then
+        echo PATH=$PATH
+        echo NODE_PATH=$NODE_PATH
+        echo NVM_PATH=$NVM_PATH
+        echo NVM_BIN=$NVM_BIN
+      fi
       echo "Now using node $VERSION"
     ;;
     "run" )