Since 1980 this has been available https://en.wikipedia.org/wiki/Uuencoding

busybox has a version https://www.busybox.net/downloads/BusyBox.html#uuencode with base64 support:

uuencode [-m] [infile] stored_filename

Uuencode a file to stdout

Options:

        -m      Use base64 encoding per RFC1521

Usage examples:

$ echo 'foo' | uuencode -m -
begin-base64 644 -
Zm9vCg==
====

And to confirm it's correct using other tools:

$ echo 'foo' | b64encode -
begin-base64 644 -
Zm9vCg==
====
$ python3 -c 'import base64; print(base64.b64encode(b"foo\n"))'
b'Zm9vCg=='