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minus=-
# standard input
fd=0
exec 3<&$fd
read line <&3
echo from stdin: $line
# close fd 3
exec 3<&${minus}
# should give `bad fd', but exact error messages vary
# read line <&3
# standard output
fd=1
exec 4>&$fd
echo to stdout >&4
exec 4>&$minus
# should give `bad fd', but exact error messages vary
# echo to stdout >&4
unset fd
# these are ambiguous redirects
exec 3<&$fd
exec 4>&$fd
exec 3>&1 4>&2
exec >&/tmp/err-and-out
echo to stdout
echo to stderr >&2
exec 1>&3 2>&4
echo /tmp/err-and-out:
cat /tmp/err-and-out
rm /tmp/err-and-out
fd=/tmp/err-and-out
exec >&$fd
echo to stdout
echo to stderr >&2
exec 1>&3 2>&4
echo /tmp/err-and-out:
cat /tmp/err-and-out
rm /tmp/err-and-out
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