We post-process history 1's output to extract the current command. This
processing needs to strip the leading history number, an optional *
character indicating whether the entry was modified (or a space), and
then a space separating character.
We were previously using sed(1) for this, but we can implement an
equivalent transformation using bash's native parameter expansion
syntax.
This also results in ~4x reduction in per-prompt command overhead.
Upstream: https://github.com/rcaloras/bash-preexec/pull/167