how do I (non-interactively) change a users password in a script ?

[user]

/bin/sh script.

Need to change a users password within the script based on a file of
user/pass I am feeding the script.

Easy.

Except the passwd command does not seem to be able to take a password as
an argument - I don't think that the passwd command can run
non-interactively.

So how is this done ?  It looks like the adduser script does it
non-interactively somehow ... but I don't see how.

Thanks.