When running a shell script, is it possible to pass specific positional parameters without having to enter them all in order?

Another way to do this thing is to name the parameter you want to declare and then do so:

{   cat >./foo 
    chmod +x ./foo
    eight=declared ./foo
    eight=declared_and_preferred \
        ./foo 1 2 3 4 5 6 7 8
    ./foo 1 2 3 4 5 6 7 8
    ./foo
} <<\SCRIPT
#!/usr/bin/sh
: ${eight:=${8:-some_default}}
printf '$eight = %s\n' "$eight"
#END
SCRIPT

OUTPUT

$eight = declared
$eight = declared_and_preferred
$eight = 8
$eight = some_default

In the above example the explicitly declared environment variable is preferred to the command-line argument, but the command-line argument is used when the environment variable is either empty or unset. When both the 8th positional and the environment variable $eight are empty or unset the default value some_default is assigned to $eight. In either case the : can be removed from the :- or := statements if empty should be an acceptable value.

The variable $eight could as well have been set like:

printf '$eight = %s\n' "${eight:=${8:-some_default}}"

... and the previous line omitted entirely but I wanted to demonstrate that declaring a variable in that way does result in a persistent value, and so I did it in two commands. Either way $eight is set to the final value of that compound parameter expansion.

getopts - for robust scripts - often is the best way to handle command options. Positional parameters, on the other hand, are almost always the most simple means of robustly handling operands in a script.

For example:

touch file$(seq -ws\ file 100)
./foo *

OUTPUT

$eight = file008

There we only see the eighth operand, but there are 101 of them globbed from my test directory.