Exclamation points in quoted strings

[Ethan Glasser-Camp]

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Hi,

I'm not a shell script pro and I don't know much about POSIX, but I
have found this puzzling behavior in bash, and although it is
documented I don't really understand why bash behaves this way. I was
hoping someone could tell me.

ethan@sundance:~$ set -H
ethan@sundance:~$ echo "hi!"
bash: !": event not found
ethan@sundance:~$ echo "hi\!"
hi\!

This is somewhat unusual; generally, characters protected by
backslashes are put through *unescaped*. Compare:

ethan@sundance:~$ echo "\`"
`
ethan@sundance:~$ echo "\""
"
ethan@sundance:~$ echo "hi\$"
hi$

The manual page does say explicitly, under "Quoting":

The backslash preceding the ! is not removed.

But no explanation is given for why this behavior exists. Is it part
of POSIX compliance? An implementation detail?

Ethan
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