feat: improve sshrm argument handling and help output

.continue/rules/project.md

@@ -0,0 +1,20 @@
+---
+description: SSHRM project conventions
+---
+
+# Project conventions
+- Use English throughout the project.
+- Keep shell scripts Bash-based when Bash is already used by the project.
+- Preserve the current behavior of the main scripts:
+  - `sshrm`: remove an entry from `~/.ssh/known_hosts` by host name or by line number.
+  - `git-release`: handle releases from `dev` to `main`, create an annotated tag, and push commits and tags.
+- Keep user-facing messages short, clear, and in English.
+- Prefer minimal, focused changes that do not alter the intent of the existing scripts.
+- 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.
+
+# Project identity
+- Main script: `sshrm`
+- Release helper: `git-release`
+- License: GNU GPL v3

sshrm

@@ -1,15 +1,60 @@
 #!/bin/bash
 
-declare -r FILENAME="${HOME}/.ssh/known_hosts"
-declare HOST=""
+set -u
 
-if [ ! "${1}" == "" ]; then
-	case "${1}" in
-		*[!0-9]*) HOST=${1} ;;
-		*) HOST=$(sed -n -e ${1}p "${FILENAME}" | awk '{print $1}') ;;
-	esac
-	ssh-keygen -R "${HOST}"
-else
-	echo "Error: No host or line number provided !"
-	echo "sshrm host|line_number"
+readonly FILENAME="${HOME}/.ssh/known_hosts"
+
+check_known_hosts() {
+	if [ ! -f "${FILENAME}" ]; then
+		error "known_hosts not found."
+		exit 1
 	fi
+}
+
+usage() {
+	echo "Usage: sshrm [-h|--help] host|line_number"
+}
+
+error() {
+	echo "Error: $1"
+}
+
+is_number() {
+	case "$1" in
+		''|*[!0-9]*) return 1 ;;
+		*) return 0 ;;
+	esac
+}
+
+get_host_from_line() {
+	awk -v line="$1" 'NR == line {print $1; exit}' "${FILENAME}"
+}
+
+remove_host() {
+	ssh-keygen -R "$1"
+}
+
+if [ "${1-}" = "" ]; then
+	error "missing argument."
+	usage
+	exit 1
+fi
+
+if [ "$1" = "-h" ] || [ "$1" = "--help" ]; then
+	usage
+	exit 0
+fi
+
+check_known_hosts
+
+if is_number "$1"; then
+	HOST="$(get_host_from_line "$1")"
+	if [ "${HOST}" = "" ]; then
+		error "invalid line number."
+		exit 1
+	fi
+else
+	HOST="$1"
+fi
+
+remove_host "$HOST"