echo "[${!-unset}]"
sleep 0.1 | cat & echo "[$!]" | tr 0-9 N
(sleep 0.1) & echo "[$!]" | tr 0-9 N
: & echo "[$!]" | tr 0-9 N
x=; $x >/tmp/rv2-empty; ls /tmp/rv2-empty; rm -f /tmp/rv2-empty
$(false) >/tmp/rv2-empty2; echo $?; ls /tmp/rv2-empty2; rm -f /tmp/rv2-empty2
echo $((0 && 1/0)) $((1 || 1/0)) $((1 ? 2 : 1/0))
A=1 B=$(true)$A sh -c 'echo "[$B]"'
A=1 B=$(echo $A) sh -c 'echo "[$B]"'
printf 'a\\ b c\n' | { read x y; echo "[$x][$y]"; }
printf 'a\\\\\nb\n' | { read x; echo "[$x]"; }
printf 'a : b\n' | { IFS=': ' read x y z; echo "[$x][$y][$z]"; }
printf 'x:y:\n' | { IFS=: read a b; echo "[$a][$b]"; }
printf 'x:y:z\n' | { IFS=: read a b; echo "[$a][$b]"; }
printf '  a  b  \n' | { read a; echo "[$a]"; }
printf 'a\n' | { IFS= read -r a b; echo "[$a][$b]"; }
case a in [[:alpha:]]) echo y;; *) echo n;; esac
case b in [!a]) echo y;; *) echo n;; esac
for i in 1 2; do [ $i = 2 ] && continue; false; done; echo $?
for i in 1 2; do false; [ $i = 1 ] || break; done; echo $?
./nosuch; echo $?
echo x >&5; echo st=$?
cat <&4; echo st=$?
x='a  b'; for w in $x "$x" ''; do echo "[$w]"; done
x=' a '; echo "[$x]" [$x] [${x}x]
cd /; echo e* | cut -c1-20
(cd /etc; echo pass*); echo pas*
(cd /; cd etc; echo host*)
x='*'; echo "$x" $x | head -c 30; echo
x='/etc/pass\wd'; echo $x
echo ${x:-a  b} "${x:-a  b}"
echo ${HOME+"q"}
i=0; until [ $i -ge 2 ]; do i=$((i+1)); echo $i; done; echo $?
while false; do :; done; echo $?
if false; then :; fi; echo $?
echo $((08))
echo $((1-$x))
x=-3; echo $((1-$x))
x=' 5'; echo $((x+1))
echo $(( 2 ** 3 ))
echo $((1<<63)) $((9223372036854775807+1))
echo $((-9223372036854775807-1)) $(( (-9223372036854775807-1) / -1 ))
v=$(printf 'a\n\n\n'); echo "[$v]"
v=$(printf '\n\na'); echo "[$v]"
echo $(printf 'a\nb') | od -c | head -2
