the important part missing in my example is the 'vice versa'. the canonical example is:
> sledge() { tr ab ba < $1 | sponge $1 }
then, you might undo a change you already -p added.
more convincing might be (using gnu sed):
> sledge() { sed -i s/identifier/long_identifier/ $1 }
a second iteration will eventually generate long_long_identifier.
