By default, placeholder expressions are automatically quoted to ensure
they are safely passed as arguments to external programs.
The r flag ({r}, {r1}, etc.) disables this behavior, outputting the
evaluated value without quotes.
For example,
echo 'foo bar' | fzf --preview 'echo {} {r}'
The preview command becomes:
echo 'foo bar' foo bar
Since `{r}` expands to unquoted "foo bar", 'foo' and 'bar' are passed
as separate arguments.
**Use with caution** Unquoted output can lead to broken commands.
echo "let's go" | fzf --preview 'echo {r}'
Close #4330