I have a following loop that works well:

function uppercase_all_letters() {
  for filename in *;
    do echo "${filename^^}";

How do I provide "${filename^^}" as a parameter to the function?

I tried it the usual well (SUBSTITUTION="${filename^^}") but then Bash reports:

./test.sh: line 26: ${filename^^}: bad substitution
  • You are obviously not running the code with bash, but possibly with dash (/bin/sh on some Linuxes) or zsh, although dash would have said Bad substitution (upper case B) and would also have complained about the non-standard function definition.
    – Kusalananda
    Jul 17, 2019 at 6:48
  • @Kusalananda Only bash is using that error format; eg. echo '${foo&&}' | bash => bash: line 1: ${foo&&}: bad substitution. The OP is probably using some older version of bash which didn't support yet that syntax.
    – user313992
    Jul 17, 2019 at 7:53
  • Could you please mention the version of bash that you use? The ^^ thing was added in bash-4.0-alpha.
    – Kusalananda
    Jul 17, 2019 at 7:58
  • @mosvy I think I misunderstood what the user wanted. It would have made more sense if the code that uses $SUBSTITUTION (and which is what probably causes the error) was shown.
    – Kusalananda
    Jul 17, 2019 at 8:03
  • Yes, but who's printing that error? ;-)
    – user313992
    Jul 17, 2019 at 8:04

1 Answer 1


To do it literally, you'd probably have to resort to eval:

function subst_all_filenames() {
    for filename in *
        eval 'echo ${filename'"$subst"'}'

subst_all_filenames "^^"
subst_all_filenames ",,"
subst_all_filenames ""

Alternatively, support only a known list of substitutions:

function subst_all_filenames() {
    case "$1" in
      ^^) for filename in *; do echo "${filename^^}"; done ;;
      ,,) for filename in *; do echo "${filename,,}"; done ;;
       *) printf "%s\n" * ;;

Sometimes such a helper function also isn't even necessary in the first place. It's quite normal to have such loops all over the place in a shell script.


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