feat: add optional known_hosts backup control to sshrm

.continue/rules/project.md

@@ -11,7 +11,7 @@ description: SSHRM project conventions
 - Prefer minimal, focused changes that do not alter the intent of the existing scripts, unless the script behavior is intentionally updated.
 - Maintain `.continue/rules/project.md` whenever project conventions or script behavior change.
 - `sshrm` is implemented as a small Bash script with helper functions, while preserving host and line-number removal behavior.
-- `sshrm` should print a short usage line, support `-h`/`--help`, and fail clearly on missing or invalid line-number input.
+- `sshrm` should print a short usage line, support `-h`/`--help`, fail clearly on missing or invalid line-number input, and may support a dedicated `--no-backup` option with a `known_hosts.sshrm.bak` backup file.
 
 # Project identity
 - Main script: `sshrm`

sshrm

@@ -3,6 +3,7 @@
 set -u
 
 readonly FILENAME="${HOME}/.ssh/known_hosts"
+readonly BACKUP_FILE="${FILENAME}.sshrm.bak"
 
 check_known_hosts() {
 	if [ ! -f "${FILENAME}" ]; then
@@ -12,7 +13,7 @@ check_known_hosts() {
 }
 
 usage() {
-	echo "Usage: sshrm [-h|--help] host|line_number"
+	echo "Usage: sshrm [-h|--help] [--no-backup] host|line_number"
 }
 
 error() {
@@ -30,6 +31,10 @@ get_host_from_line() {
 	awk -v line="$1" 'NR == line {print $1; exit}' "${FILENAME}"
 }
 
+create_backup() {
+	cp "${FILENAME}" "${BACKUP_FILE}"
+}
+
 remove_host() {
 	ssh-keygen -R "$1"
 }
@@ -45,6 +50,18 @@ if [ "$1" = "-h" ] || [ "$1" = "--help" ]; then
 	exit 0
 fi
 
+	backup=true
+if [ "$1" = "--no-backup" ]; then
+	backup=false
+	shift
+fi
+
+if [ "${1-}" = "" ]; then
+	error "missing argument."
+	usage
+	exit 1
+fi
+
 check_known_hosts
 
 if is_number "$1"; then
@@ -57,4 +74,8 @@ else
 	HOST="$1"
 fi
 
+if [ "${backup}" = true ]; then
+	create_backup
+fi
+
 remove_host "$HOST"