Not strictly a C++ gag, but seasonal:
#!/bin/bash
# Santa Claus is coming to town
better !pout !cry
better watchout
lpr why
santa_claus < north_pole >town
cat /etc/passwd > list
ncheck list
ncheck list
grep naughty list >coal
grep nice list >gift
santa_claus < north_pole >town
who | grep sleeping
who | grep awake
who | egrep 'bad|good'
for goodness_sake; do
be_good;
done