Bash inserting quotes into string before execution

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Because when you try to execute your command with

$cmd

only one layer of expansion happens. $cmd contains echo "hello this is a test", which is expanded into 6 whitespace-separated tokens:

  1. echo
  2. "hello
  3. this
  4. is
  5. a
  6. test"

and that’s what the set -x output is showing you: it’s putting single quotes around the tokens that contain double quotes, in order to be clear about what the individual tokens are.

If you want $cmd to be expanded into a string which then has all the bash quoting rules applied again, try executing your command with:

bash -c "$cmd"

or (as @bitmask points out in the comments, and this is probably more efficient)

eval "$cmd"

instead of just

$cmd

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