LINUX :
1.Login with sybase or syb<sid>
2.Set the environment variables from a command line prompt by running one of the following environment scripts
SYBASE.csh or SYBASE.sh
below command is used to check the env variables
echo $SYBASE
highlighted area should be displayed with sybase env variables if not need to execute below command
WINDOWS : you need to execute the SYBASE.bat which is located on sybase home directory .
Login with isql as shown in fig below
NOTE : Login procedure is same for LINUX and WINDOWS