bin/assert-arg: Add helper utility

1 files changed, 78 insertions, 0 deletions

diff --git a/bin/assert-arg b/bin/assert-arg
new file mode 100755
index 0000000..d7bc8f4
--- /dev/null
+++ b/bin/assert-arg
@@ -0,0 +1,78 @@
+#!/bin/sh
+set -eu
+
+usage() {
+	cat <<-'EOF'
+		Usage:
+		  assert-arg STRING MESSAGE
+		  assert-arg -h
+	EOF
+}
+
+help() {
+	cat <<-'EOF'
+
+		Options:
+		  -h, --help    show this message
+
+		  STRING        the string to check if is empty
+		  MESSAGE       the message to print when STRING is empty
+
+
+		Examples:
+
+		  Assert that $1 contains an argument, named FILENAME:
+
+		    $ eval "$(assert-arg "${1:-}" 'FILENAME')"
+	EOF
+}
+
+
+for flag in "$@"; do
+	case "$flag" in
+		--)
+			break
+			;;
+		--help)
+			usage
+			help
+			exit
+			;;
+		*)
+			;;
+	esac
+done
+
+while getopts 'h' flag; do
+	case "$flag" in
+		h)
+			usage
+			help
+			exit
+			;;
+		*)
+			usage >&2
+			exit 2
+			;;
+	esac
+done
+shift $((OPTIND - 1))
+
+
+STRING="${1:-}"
+MESSAGE="${2:-}"
+
+if [ -z "$MESSAGE" ]; then
+	printf 'Missing MESSAGE, an argument to assert-arg.\n\n' >&2
+	usage >&2
+	exit 2
+fi
+
+
+if [ -z "$STRING" ]; then
+	printf 'Missing %s.\n\n' "$MESSAGE" >&2
+	cat <<-'EOF'
+		usage >&2
+		exit 2
+	EOF
+fi