How to export a function in Bourne shell?

Question

Is it possible to export a function in Bourne shell (sh)?

The answers in this question indicate how to do so for bash, ksh and zsh, but none say whether sh supports it.

If sh definitely does not allow it, I won't spend any more time searching for it.

Answer 1

No, it is not possible.

The POSIX spec for export is quite clear that it only supports variables. typeset and other extensions used for the purpose in more recent shells are just that -- extensions -- not present in POSIX.

Answer 2

No. The POSIX specification for export lacks the -f present in bash that allows one to export a function.

A (very verbose) workaround is to save your function to a file and source it in the child script.

script.sh:

#!/bin/sh --

function_holder="$(cat <<'EOF'
    function_to_export() {
        printf '%s\n' "This function is being run in ${0}"
    }
EOF
)"

function_file="$(mktemp)" || exit 1

export function_file

printf '%s\n' "$function_holder" > "$function_file"

. "$function_file"

function_to_export

./script2.sh

rm -- "$function_file"

script2.sh:

#!/bin/sh --

. "${function_file:?}"

function_to_export

Running script.sh from the terminal:

[user@hostname /tmp]$ ./script.sh
This function is being run in ./script.sh
This function is being run in ./script2.sh