magic-space expand sequence referring to the command history in place, so you have a chance to review before executing.
\set prompt="SQL> "
\set semicolon_hack=on
\set date="%Y-%m-%d"
\set datetime="%Y-%m-%d %H:%M:%S"
# \set colwidth=20
# \set style=pretty
# \set style=csv
# \set style=vert
# \set style=horiz
\set style=bcp