command "shifts away" one command-line parameter.
You can shift three times if there are three command-line parameters.
Many shells also can take an argument, like shift 3, that tells
how many times to shift; on those shells, you can
to unset all parameters.
The portable way to unset all command-line parameters is probably toa single dummy parameter, then shift it away:
set x shift
Setting the single parameter wipes out whatever other parameters were set before.