add usage() and die()

sxbm

@@ -24,3 +24,24 @@ ENCRYPTION="0"
 
 # Auto fetch title. 1 to enable, 0 to disable
 TITLE_FETCH="1"
+
+die(){
+  [ -z "$1" ] ||
+    printf "$@\n" > /dev/stderr
+  exit 1
+}
+
+usage(){
+  printf "Usage: sxbm <command> [<args>]\n"
+  printf "
+COMMANDS:
+    add           <link> [title] [+tags]
+    ls|list       [-c|--disable-colors] [title] [+tags]
+    open          [-f|--force] <line_num|title|+tags>
+    rm|remove     [-f|--force] <line_num|title|+tags>
+    edit          [line_num|title|+tags]
+    -h|--help     print this text and exit
+    -v|--version  print the version and exit\n\n"
+}
+
+[ -z "$1" ] && usage && die