Mass setting user passwords

Ever need to change (or set) passwords for a large number of users?  Something like this code snippet may help.

# find all the usernames with bash logins
usernames=$(cat /etc/passwd  | grep bash | sed 's/:.*//g)
for user in $usernames; do 
    echo "somepassword" | passwd --stdin $user
done

The --stdin option does not work in all version of passwd (e.g. it does not work on the Debian/Ubuntu-based versions).  Instead, the chpasswd command works everywhere (so is probably the better option):

# find all the usernames with bash logins
usernames=$(cat /etc/passwd  | grep bash | sed 's/:.*//g)
for user in $usernames; do 
    echo "$user:somepassword" | chpasswd
done