$ pm_1196515_option_processing.pl
Option starting values:
Options: x[42] y[fred] z[1.0]

$ export USER_OPTS='-z 1.5'

$ pm_1196515_option_processing.pl
Option starting values:
Options: x[42] y[fred] z[1.0]
After environment variable options processed:
Options: x[42] y[fred] z[1.5]

$ pm_1196515_option_processing.pl -x 21
Option starting values:
Options: x[42] y[fred] z[1.0]
After environment variable options processed:
Options: x[42] y[fred] z[1.5]
After command line options processed:
Options: x[21] y[fred] z[1.5]

$ pm_1196515_option_processing.pl -y wilma -z 3.4
Option starting values:
Options: x[42] y[fred] z[1.0]
After environment variable options processed:
Options: x[42] y[fred] z[1.5]
After command line options processed:
Options: x[42] y[wilma] z[3.4]