Stringify bash command from array of arguments for use in "bash -c"

Question

I would like to stringify a given command, given as an array.

This would be useful to for example put a command inside a bash -c.

For example :

cmd=(
  "printf '%s\n'"
  "foo bar"
  "baz bang"
)

stringified="$(transform "${cmd[@]}")"

So that : "${cmd[@]}" and bash -c "$stringified" would give the exact same output for any cmd array.

In my example, that would be :

$ "${cmd[@]}"
foo bar
baz bang

The value of stringified="printf \"%s\n\" \"foo bar\" \"baz bang\"" works for my case, but I wish to have a transform function that would properly escape those arguments for me.

Preferably, I would prefer a bash solution, or if that is not the case, with tools that are usually already installed on a linux distribution (printf, echo).

Answer 1

I found a good solution for this (I think it would work for any input array), it uses the printf "%q" feature.

You can just write :

cmd=(
  "printf '%s\n'"
  "foo bar"
  "baz bang"
)

stringified="$(printf "%q " "${cmd[@]}")"

This gives :

printf\ \'%s\\n\' foo\ bar baz\ bang

Explanation

The printf "%q" command escapes characters to be used in shell :

%q ARGUMENT is printed in a format that can be reused as shell input, escaping non-printable characters with the proposed POSIX $'' syntax.

Source : man printf

By using "%q ", all elements in the array are printed and correctly escaped, and since there is a space after the %q, all elements will be delimited by a space.