Brace expansion with $@ arguments

You can use:

command "${@/#/foo}" "${@/#/bar}"

This uses the substitute variant of shell parameter expansion. The # anchors the match to the start of the parameter.

$ set -- a abc xyz$ echo command "${@/#/foo}" "${@/#/bar}"command fooa fooabc fooxyz bara barabc barxyz$

Is there a way to scale this for larger {foo,bar,baz,...}$@ or {foo,bar}{123,456}$@?

Yes, but you would end up using arrays:

$ set -- a abc xyz$ args=( "$@" )$ for prefix in foo bar baz who why; do prefixed1+=( "${args[@]/#/$prefix}" ); done$ echo command "${prefixed1[@]}"command fooa fooabc fooxyz bara barabc barxyz baza bazabc bazxyz whoa whoabc whoxyz whya whyabc whyxyz$

Or (noting that you have to get the sequencing correct):

$ for prefix in 123 456; do prefixed1+=( "${args[@]/#/$prefix}" ); done$ for prefix in foo bar; do prefixed2+=( "${prefixed1[@]/#/$prefix}" ); done$ echo command "${prefixed2[@]}"command foo123a foo123abc foo123xyz foo456a foo456abc foo456xyz bar123a bar123abc bar123xyz bar456a bar456abc bar456xyz$

Note that this preserves spaces in arguments:

$ unset prefixed1 prefixed2$ set -- 'a b' 'x y z'$ args=( "$@" )$ for prefix in 'p p-' '123 456 '; do prefixed1+=( "${args[@]/#/$prefix}" ); done$ echo command "${prefixed1[@]}"command p p-a b p p-x y z 123 456 a b 123 456 x y z$ for prefix in 'foo 1-' 'bar 2-'; do prefixed2+=( "${prefixed1[@]/#/$prefix}" ); done$ echo command "${prefixed2[@]}"command foo 1-p p-a b foo 1-p p-x y z foo 1-123 456 a b foo 1-123 456 x y z bar 2-p p-a b bar 2-p p-x y z bar 2-123 456 a b bar 2-123 456 x y z$ printf "[%s]\n" "${prefixed2[@]}"[foo 1-p p-a b][foo 1-p p-x y z][foo 1-123 456 a b][foo 1-123 456 x y z][bar 2-p p-a b][bar 2-p p-x y z][bar 2-123 456 a b][bar 2-123 456 x y z]$

And the first loop could be:

for prefix in 'p p-' '123 456 '; do prefixed1+=( "${@/#/$prefix}" ); done

without using the ${args[@]} array.