Added code to display usage options in bldpkg

bldpkg

@@ -75,23 +75,37 @@ genchecksum() {
   exit 0
 }
 
-# If the first argument is "genchecksum", invoke the genchecksum function. 
-# Else if the first argument is filename, then get the build extension of that file and source it, else throw an error
-# Else if no argument is given, get the basename of the directory and look for a matching package build file name. 
-# If a package build file is found,  source that file and that will initiate the build.
-if [ -n "$1" ] && [ "$1" = "genchecksum" ] ; then
-  genchecksum
-elif [ -n "$1" ] ; then
-  source "$1"
-elif [ -z "$1" ] && [ -f "$srcdirpath.SMBuild" ]; then
-  source "$srcdirpath.SMBuild"
-else
-  echo "[ERROR] Please provide a build file as an argument"
-  exit 1
-fi
+help() {
+cat << EOF
+Bash script for building SMLinux-compatible packages from source.
 
-# Sanitise the build file, get what we need.
-# If any of the following variables are not set in the build file, abort.
+Usage: 
+  -g | g | gen : Generate sha512 checksums of all tarballs and patches and put them into the package build file
+
+  -h | h | help : Show this message
+
+  If no arguments are provided, this script attempts to build a package provided the package build file and the parent directory name matches.
+EOF
+exit 0
+}
+
+case "$1" in
+  -g|g|gen)
+  genchecksum
+  ;;
+  -h|h|help)
+  help
+  ;;
+  *)
+  if [ -f "$srcdirpath.SMBuild" ]; then
+    source "$srcdirpath.SMBuild"
+  else
+    echo "No suitable package build file found to source from. Aborting!"
+    exit 1
+  fi
+esac
+
+# Validate the build file. If any of the following variables are not set in the build file, abort.
 for buildvariables in app version build homepage desc requires ; do
   if [[ ! "${!buildvariables}" ]] ; then
     echo "[ERROR] Required variable \"${buildvariables}\" is not set. Please check your build file. Aborting!"