.vim/hooks/pre-session-save: Delete older than 30 days

.vim/hooks/pre-session-save

@@ -1,3 +1,4 @@
-#!/bin/sh
-
-cp $HOME/.vim/sessions/session.vim $HOME/.vim/sessions/session-$(date +%d-%b-%Y-%H:%M:%S).vim
+#!/bin/sh -eu
+cd "$HOME/.vim/sessions" || exit 1
+cp session.vim "session-$(date +%d-%b-%Y-%H:%M:%S).vim"
+find ./*.vim -type f -mtime +31 -delete