Functions to backup a function and remove a backed up function

functions/backup_function.fish

+function backup_function
+    set -l funcname $argv[1]
+
+    if functions -q -- $funcname
+        _create_tmpname
+        functions -- $funcname | sed -e s/^function\ $funcname/function\ old_$funcname/ > $tmpname
+        _source_old_function
+    else
+        _print_function_not_found $argv
+        remove_backup_function $argv
+        return 1
+    end
+end
+
+function _create_tmpname
+    set -l TMPDIR /tmp
+
+    set -g tmpname (printf "$TMPDIR/fish_funced_%d_%d.fish" %self (random))
+    while test -f $tmpname
+        set -g tmpname (printf "$TMPDIR/fish_funced_%d_%d.fish" %self (random))
+    end
+end
+
+function _print_function_not_found
+    set_color red
+    _ "Function '$argv' not found.
+"
+    set_color normal
+end
+
+function _source_old_function
+    . $tmpname
+end

functions/remove_backup_function.fish

+function remove_backup_function
+    functions -e old_$argv[1]
+
+    rm $tmpname >/dev/null ^&1
+    set -e tmpname
+end