source: vendor/bash/3.1/tests/exec6.sub

# builtins with exit status inverted

( true )
echo $?
( ! true )
echo $?

( false )
echo $?
( ! false )
echo $?

# inverting shouldn't affect exit
(exit 42)
echo $?

( ! exit 42 )
echo $?

# commands requiring an exec with exit status inverted -- broken in bash-2.04

( ls > /dev/null 2>&1 )
echo $?
( ! ls > /dev/null 2>&1 )
echo $?

touch /tmp/notwrite
chmod 400 /tmp/notwrite

# make sure redirection failures in commands whose exit status is inverted
# are handled correctly

( ls > /tmp/notwrite ) 2>/dev/null
echo $?

( ! ls > /tmp/notwrite ) 2>/dev/null
echo $?

# now add exit traps, true and false for commands with and without exit
# status inversion

(trap 'false' 0 ; ! ls > /tmp/notwrite ) 2>/dev/null
echo $?

(trap 'false' 0 ; ls > /tmp/notwrite ) 2>/dev/null
echo $?

(trap 'true' 0 ; ! ls > /tmp/notwrite ) 2>/dev/null
echo $?

(trap 'true' 0 ; ls > /tmp/notwrite ) 2>/dev/null
echo $?

rm -f /tmp/notwrite