amend! first steps with command line args

first steps with command line args

shopts.sh

@@ -0,0 +1,63 @@
+#!/bin/bash
+# ex33.sh: Exercising getopts and OPTIND
+#          Script modified 10/09/03 at the suggestion of Bill Gradwohl.
+
+
+# Here we observe how 'getopts' processes command-line arguments to script.
+# The arguments are parsed as "options" (flags) and associated arguments.
+
+# Try invoking this script with:
+#   'scriptname -mn'
+#   'scriptname -oq qOption' (qOption can be some arbitrary string.)
+#   'scriptname -qXXX -r'
+#
+#   'scriptname -qr'
+#+      - Unexpected result, takes "r" as the argument to option "q"
+#   'scriptname -q -r' 
+#+      - Unexpected result, same as above
+#   'scriptname -mnop -mnop'  - Unexpected result
+#   (OPTIND is unreliable at stating where an option came from.)
+#
+#  If an option expects an argument ("flag:"), then it will grab
+#+ whatever is next on the command-line.
+
+NO_ARGS=0 
+E_OPTERROR=85
+
+if [ $# -eq "$NO_ARGS" ]    # Script invoked with no command-line args?
+then
+  echo "Usage: `basename $0` options (-mnopqrs)"
+  exit $E_OPTERROR          # Exit and explain usage.
+                            # Usage: scriptname -options
+                            # Note: dash (-) necessary
+fi  
+
+
+while getopts ":mnopq:rs" Option
+do
+  case $Option in
+    m     ) echo "$OPTIND -$Option ($OPTARG)";;
+    n | o ) echo "$OPTIND -$Option ($OPTARG)";;
+    p     ) echo "$OPTIND -$Option ($OPTARG)";;
+    q     ) echo "$OPTIND -$Option ($OPTARG)";;
+    #  Note that option 'q' must have an associated argument,
+    #+ otherwise it falls through to the default.
+    r | s ) echo "$OPTIND -$Option ($OPTARG)";;
+    *     ) echo "Unimplemented option chosen.";;   # Default.
+  esac
+done
+
+shift $(($OPTIND - 1))
+echo "Rest $@"
+
+#  Decrements the argument pointer so it points to next argument.
+#  $1 now references the first non-option item supplied on the command-line
+#+ if one exists.
+
+exit $?
+
+#   As Bill Gradwohl states,
+#  "The getopts mechanism allows one to specify:  scriptname -mnop -mnop
+#+  but there is no reliable way to differentiate what came
+#+ from where by using OPTIND."
+#  There are, however, workarounds.