feat: Update optval()

src/boring-backup

@@ -63,21 +63,25 @@ EOF
 optval() {
     # GNU-style CLI options parser.
     #
-    # Parse --opt VAL and --opt=VAL options.
-    # Requires 2 arguments: $1, $2.
-    # Set variables:
-    #   opt     option name.
-    #   val     option value.
-    #   sft     value for shift.
+    # Parse `--opt VAL` and `--opt=VAL` options.
+    # Usage: optval "$1" "$2"
+    # Sets variables:
+    #   opt - option name
+    #   val - option's value
+    #   sft - value for shift
 
-    if [[ "$1" =~ .+=.+ ]]; then
-        opt="${1%%=*}"; val="${1#*=}"; sft=1
-    elif [[ ! "$1" =~ .+=$ ]] && [ "$2" ] && [ "${2:0:1}" != "-" ]; then
-        opt="$1"; val="$2"; sft=2
-    else
-        opt="$1"
-        if [[ "$1" =~ .+=$ ]]; then opt="${1:0: -1}"; fi
-        echo "Error: Missing argument for $opt" >&2; exit 1
+    opt="${1%%=*}"; val="${1##*=}"; sft=1
+
+    if [ "$opt" == "$val" ]; then
+        if [ -n "$2" ] && [ "${2:0:1}" != "-" ]; then
+            val="$2"; sft=2
+        else
+            unset val
+        fi
+    fi
+
+    if [ -z "$val" ]; then
+        echo "Missing argument for option $opt" >&2; exit 1
     fi
 }