To be clear: both alternatives shown below will invoke the same thing (`command -v gtimeout`).

    if [ -x "$(command -v gtimeout)" ]; then

and

    if command -v gtimeout >/dev/null; then

The first invokes it in a sub shell (and captures the output), the second invokes it directly and discards the output, using the return status of `command` as the input to `if`.

The superficial reason the second is "preferred" is that it's slightly better performance wise. Not a huge difference, but it is a difference.

However the hidden, and probably more impactful reason it's preferred, is that the first can give a false negative. If the thing you want to test before calling is implemented as a shell builtin, it will fail, because the `-x` mode of `test` (and thus `[`) is a file test, whereas the return value of `command -v` is whether or not the command can be invoked.

Ah! I misread the parent, if thought he meant `if command` to look for a random command (e.g. `if grep`)