filterHistory improvements

Add existence check for given file. (How did I forget that?)
Create automatic backup in temporary directory and use it to show
overview of deleted commands.
Make sed expression more readable by using double quotes for the whole
regex and escaping the $ instead of a mix between single and double.

.local/bin/filterHistory

@@ -1,6 +1,7 @@
 #!/bin/bash
 
 [ $# -eq 1 ] || { echo "Specify history file" >&2; exit 1; }
+[ -e "$1" ] || { echo "File does not exist" >&2; exit 1; }
 [ "$(stat -c '%a' "$1")" = "600" ] || { echo "File does not look like a history file" >&2; exit 1; }
 
 declare -a COMMANDS
@@ -30,8 +31,17 @@ echo "Are you a 100% sure you want to delete these commands from $1? (Type out y
 read yn
 [ "$yn" = "yes" ] || exit 1
 
+tempd="$(mktemp -d)"
+cp "$1" "$tempd/$(basename "$1")"
+echo "Backup created at $tempd/$(basename "$1")"
+echo
+
 for c in "${COMMANDS[@]}"; do
 	c="$(echo "$c" | sed 's/\./\\./g; s/\//\\\//g')"
-	sed -Ei '/^: [0-9]+:[0-9]+;'"$c"'$/d' "$1"
+	sed -Ei "/^: [0-9]+:[0-9]+;${c}\$/d" "$1"
 	echo "$c deleted"
 done
+
+echo
+echo "Following commands were deleted:"
+diff "$1" "$tempd/$(basename "$1")" | grep "^>" | cut -d\; -f 2 | sort | uniq -c | sort -nr