Linux and OS X come with the Makekey Command installed, usually in /usr/libexec/makekey. You can use this binary to create /etc/passwd file entries of hashed passwords. To use the command, simply pipe some text into the command. Here, we’ll Echo Testpassword into makekey:

echo testpassword | /usr/libexec/makekey

And we’ll get a simple output, such as:

woNH11o4mqvAc

There are certainly other ways to do something like this, but when writing a script you may use in either a Linux or OS X environment, this is one place where you should have a modicum of success crossing platforms.