Usually, you choose a string format that is compatible, as passing binary date-time is a compiled code deal, not scripting. I like "YYYY-mm-dd HH:MM:SS.ssssss" but your SQL engine may vary. ...
I gather you are using the sqlcmd client on the UNIX side. The sqlcmd -v switch (at least on the dos version is for the purpose of passing variables into the embeddeded SQL input file.