Check getopt(1) version, fix usage note on misuse

Check whether the version of getopt(1) is the GNU one that supports
preserving whitespace and special characters and long options, or the
BSD one that doesn't support either (as is the default on OS X, for
example). Fall back to short options only and print a warning if the old
version is detected.

Additionally, since set -e is used, deal with getopt(1) errors in a way
that actually prints the usage information as originally intended rather
than exiting right away after getopt's message.

Closes: #1

Author: neverpanic

README.md

@@ -12,7 +12,7 @@ To run this script, you will need:
 
  - Bash (>= 4.x)
  - curl
- - getopt
+ - getopt, preferrably a version that preserves quoted whitespace and long options
  - tput
  - fmt
  - sed, in a version that has extended regex support using either `-E` (BSD) or `-r` (GNU)

google-font-download

@@ -117,14 +117,46 @@ misuse_exit() {
 	usage
 }
 
+# Check for modern getopt(1) that quotes correctly; see #1 for rationale
+ret=0
+modern_getopt=1
+getopt -T >/dev/null || ret=$?
+if [ $ret -ne 4 ]; then
+	modern_getopt=0
+fi
+
 # Parse options
-temp=$(getopt -o f:hl:o: --long format:,help,languages:,output -n "${0:-google-font-download}" -- "$@")
-if [ $? != 0 ]; then
-	echo >&2
-	usage
+if [ $modern_getopt -eq 1 ]; then
+	ret=0
+	temp=$(getopt -o f:hl:o: --long format:,help,languages:,output -n "${0:-google-font-download}" -- "$@") || ret=$?
+	if [ $ret -ne 0 ]; then
+		echo >&2
+		usage
+	fi
+else
+	cols=$(tput cols) || cols=80
+	fmt $(( cols - 8 )) $cols >&2 <<-EOF
+		Warning: Old getopt(1) detected.
+
+		Your version of getopt(1) does not correctly deal with whitespace and does not support long options. You may
+		have to quote any special character arguments twice. For example, to download the 'Open Sans' font, use $0
+		"'Open Sans'". See https://github.com/neverpanic/google-font-download/issues/1 for more information.
+
+		You should consider upgrading to a more modern version of getopt(1).
+
+	EOF
+
+	ret=0
+	temp=$(getopt f:hl:o: $*) || ret=$?
+	if [ $ret -ne 0 ]; then
+		echo >&2
+		usage
+	fi
 fi
 
 # Process arguments
+# For the non-modern getopt(1), the eval and quoting is a hack to allow users to manually specify values that have been
+# quoted twice.
 eval set -- "$temp"
 while true; do
 	case "$1" in