$ pda set url@evf https://example.com
$ fecho tmpval hello world
$ pda set greeting@evf < tmpval
$ pda set number@evf 42
$ pda export evf --value "**https**"
{"key":"url","value":"https://example.com","encoding":"text"}
$ pda export evf --value "**world**"
{"key":"greeting","value":"hello world\n","encoding":"text"}