# first try some invalid patterns (do in subshell due to parsing error)
"$THIS_SH" -c 'echo ${-}'
"$THIS_SH" -c 'echo ${:-}'

# now some funky ones
echo _${#-} _${#:-}

# now some valid ones
set --
echo _$1 _${1-} _${1:-} _${1-word} _${1:-word}

set -- aaaa
echo _$1 _${1-} _${1:-} _${1-word} _${1:-word}

unset f
echo _$f _${f-} _${f:-} _${f-word} _${f:-word}

f=
echo _$f _${f-} _${f:-} _${f-word} _${f:-word}

f=fff
echo _$f _${f-} _${f:-} _${f-word} _${f:-word}
