Mangle long-option names to allow dashes

Fixes problem where long options with dashes, like `--no-color` were
 broken. This was due to the fact that bash variable names must match
 `[_a-zA-Z][_0-9a-zA-Z]*` and the usage parsing and option handling was
 trying to create variables with dashes in their names. Short of
 employing Bash4 associative arrays, "name mangling" seemed like the
 best solution to this problem.

Solution: map dashes to underscores when creating bash variables in the
script that correspond to long option flags. The downside of this is
that `--no_color` and `--no-color` will collide, but users expecting to
use options that are identical except one has an underscore and the
other has a dash deserve the ensuing confusion.

main.sh

@@ -56,6 +56,8 @@ read -r -d '' usage <<-'EOF' || true # exits non-zero when EOF encountered
   -v               Enable verbose mode, print script as it is executed
   -d --debug       Enables debug mode
   -h --help        This page
+  -n --no-color    Disable color output
+  -1 --one         Do just one thing
 EOF
 
 # Set magic variables for current file and its directory.
@@ -120,14 +122,15 @@ trap cleanup_before_exit EXIT
 
 # Translate usage string -> getopts arguments, and set $arg_<flag> defaults
 while read line; do
-  # fetch single character version of option sting
+  # fetch single character version of option string
   opt="$(echo "${line}" |awk '{print $1}' |sed -e 's#^-##')"
 
   # fetch long version if present
   long_opt="$(echo "${line}" |awk '/\-\-/ {print $2}' |sed -e 's#^--##')"
+  long_opt_mangled="$(sed 's#-#_#g' <<< $long_opt)"
 
   # map long name back to short name
-  varname="short_opt_${long_opt}"
+  varname="short_opt_${long_opt_mangled}"
   eval "${varname}=\"${opt}\""
 
   # check if option takes an argument
@@ -157,6 +160,9 @@ opts="${opts}-:"
 # Reset in case getopts has been used previously in the shell.
 OPTIND=1
 
+# start parsing command line
+set +o nounset # unexpected arguments will cause unbound variables
+               # to be dereferenced
 # Overwrite $arg_<flag> defaults with the actual CLI options
 while getopts "${opts}" opt; do
   [ "${opt}" = "?" ] && help "Invalid use of script: ${@} "
@@ -166,13 +172,15 @@ while getopts "${opts}" opt; do
     if [[ "${OPTARG}" =~ .*=.* ]]; then
       # --key=value format
       long=${OPTARG/=*/}
+      long_mangled="$(sed 's#-#_#g' <<< $long)"
       # Set opt to the short option corresponding to the long option
-      eval "opt=\"\${short_opt_${long}}\""
+      eval "opt=\"\${short_opt_${long_mangled}}\""
       OPTARG=${OPTARG#*=}
     else
       # --key value format
       # Map long name to short version of option
-      eval "opt=\"\${short_opt_${OPTARG}}\""
+      long_mangled="$(sed 's#-#_#g' <<< $OPTARG)"
+      eval "opt=\"\${short_opt_${long_mangled}}\""
       # Only assign OPTARG if option takes an argument
       eval "OPTARG=\"\${@:OPTIND:\${has_arg_${opt}}}\""
       # shift over the argument if argument is expected
@@ -183,14 +191,15 @@ while getopts "${opts}" opt; do
   varname="arg_${opt:0:1}"
   default="${!varname}"
 
-  value="${OPTARG:-}"
+  value="${OPTARG}"
-  if [ -z "${OPTARG:-}" ] && [ "${default}" = "0" ]; then
+  if [ -z "${OPTARG}" ] && [ "${default}" = "0" ]; then
     value="1"
   fi
 
   eval "${varname}=\"${value}\""
   debug "cli arg ${varname} = ($default) -> ${!varname}"
 done
+set -o nounset # no more unbound variable references expected
 
 shift $((OPTIND-1))