#Using single-purpose GNU programs

###GNU Expand The expand utility works (only) as a pipeline program:

for f in "${sources[@]}"
do
     cp "$f" "$f.bak" && expand <"$f.bak" >"$f"
done

###GNU Indent The indent utility can completely re-layout your code. The option to expand tabs is -nut:

indent -nut "${sources[@]}"