Create run-hooks function and switch pre-start hook to that

- This is initial prototype of a more flexible hooks system.
- Add /usr/local/bin/before-notebook.d hooks which is run right before
  the notebook runs.

base-notebook/start.sh

@@ -11,22 +11,33 @@ else
     cmd=$*
 fi
 
-for f in /usr/local/bin/start-notebook.d/*; do
+run-hooks () {
+    # Source scripts or run executable files in a directory
+    if [[ ! -d "$1" ]] ; then
+	return
+    fi
+    echo "$0: running hooks in $1"
+    for f in "$1"/*; do
 	case "$f" in
 	    *.sh)
-      echo "$0: running $f"; . "$f"
+		echo "$0: running $f"
+		source "$f"
 		;;
 	    *)
-      if [ -x $f ]; then
+		if [[ -x "$f" ]] ; then
 		    echo "$0: running $f"
-        $f
+		    "$f"
 		else
 		    echo "$0: ignoring $f"
 		fi
 		;;
 	esac
-  echo
-done
+    echo "$0: done running hooks in $1"
+    done
+}
+
+run-hooks /usr/local/bin/start-notebook.d
+
 # Handle special flags if we're root
 if [ $(id -u) == 0 ] ; then
 
@@ -89,7 +100,7 @@ if [ $(id -u) == 0 ] ; then
 
     # Exec the command as NB_USER with the PATH and the rest of
     # the environment preserved
-    eval "$NB_PRE_START_HOOK"
+    run-hooks /usr/local/bin/before-notebook.d
     echo "Executing the command: $cmd"
     exec sudo -E -H -u $NB_USER PATH=$PATH XDG_CACHE_HOME=/home/$NB_USER/.cache PYTHONPATH=$PYTHONPATH $cmd
 else
@@ -133,7 +144,7 @@ else
     fi
 
     # Execute the command
+    run-hooks /usr/local/bin/before-notebook.d
     echo "Executing the command: $cmd"
-    eval "$NB_PRE_START_HOOK"
     exec $cmd
 fi