FreeTDS + unixODBC or iODBC
Install first FreeTDS, then configure one of the two ODBC engines to use FreeTDS as its ODBC driver. Then use the commandline interface of the ODBC engine.
unixODBC has isql, iODBC has iodbctest
You can also use your favorite programming language (I've successfully used Perl, C, Python and Ruby to connect to MSSQL)
I'm personally using FreeTDS + iODBC:
$more /etc/freetds/freetds.conf
[10.0.1.251]
host = 10.0.1.251
port = 1433
tds version = 8.0
$ more /etc/odbc.ini
[ACCT]
Driver = /usr/local/freetds/lib/libtdsodbc.so
Description = ODBC to SQLServer via FreeTDS
Trace = No
Servername = 10.0.1.251
Database = accounts_ver8
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