Use more idiomatic clargs

bin/run

@@ -1,21 +1,45 @@
 #!/usr/bin/env bash
 
+show_help() {
+    echo "usage: $0 --lang=lang --year=year --day=day"
+}
+
+language=''
+year='0'
+day='0'
+
 #
 # check args
 #
+while :; do
+    case $1 in
+	-h|-\?|--help)
+	    show_help    # Display a usage synopsis.
+	    exit
+	    ;;
+	--lang=?*)
+	    language=${1#*=}
+	    ;;
+	--year=?*)
+	    year=${1#*=}
+	    ;;
+	--day=?*)
+	    day=${1#*=}
+	    ;;
+	-?*)
+	    printf 'WARN: Unknown option (ignored): %s\n' "$1" >&2
+	    ;;
+	*)
+	    break
+    esac
 
-if [[ $# -ne 3 ]]
+    shift
-then
+done
-   echo "usage: $0 year day"
-   exit 1
-fi
 
 #
 # check year and day
 #
 
-year=$(($2))
-
 if [[ $year -lt 2015 ]]
 then
     echo "invalid year: $2"
@@ -23,8 +47,6 @@ then
     exit 2
 fi
 
-day=$(($3))
-
 if [[ $day -lt 1 ]] || [[ $day -gt 25 ]]
 then
     echo "invalid day: $3"
@@ -55,7 +77,6 @@ then
     curl -s -b "$(cat ../cookie)" $input_url > $input_path
 fi
 
-language=$1
 valid_languages=""
 valid_language="false"