Add 'examples/shell/shortcuts/getargs.sh'

examples/shell/shortcuts/getargs.sh

@@ -0,0 +1,56 @@
+#!/bin/sh
+# POSIX
+
+# Reset all variables that might be set
+file=
+verbose=0 # Variables to be evaluated as shell arithmetic should be initialized to a default or validated beforehand.
+
+while :; do
+    case $1 in
+        -h|-\?|--help)   # Call a "show_help" function to display a synopsis, then exit.
+            show_help
+            exit
+            ;;
+        -f|--file)       # Takes an option argument, ensuring it has been specified.
+            if [ -n "$2" ]; then
+                file=$2
+                shift
+            else
+                printf 'ERROR: "--file" requires a non-empty option argument.\n' >&2
+                exit 1
+            fi
+            ;;
+        --file=?*)
+            file=${1#*=} # Delete everything up to "=" and assign the remainder.
+            ;;
+        --file=)         # Handle the case of an empty --file=
+            printf 'ERROR: "--file" requires a non-empty option argument.\n' >&2
+            exit 1
+            ;;
+        -v|--verbose)
+            verbose=$((verbose + 1)) # Each -v argument adds 1 to verbosity.
+            ;;
+        --)              # End of all options.
+            shift
+            break
+            ;;
+        -?*)
+            printf 'WARN: Unknown option (ignored): %s\n' "$1" >&2
+            ;;
+        *)               # Default case: If no more options then break out of the loop.
+            break
+    esac
+
+    shift
+done
+
+# if --file was provided, open it for writing, else duplicate stdout
+if [ -n "$file" ]; then
+    exec 3> "$file"
+else
+    exec 3>&1
+fi
+
+# Rest of the program here.
+# If there are input files (for example) that follow the options, they
+# will remain in the "$@" positional parameters.