#!/usr/bin/ksh

ValUniqueNo=0
export ValUniqueNo

FnGenerateUniqueNo()
{
(( ValUniqueNo = $ValUniqueNo + 1 ))
echo $ValUniqueNo
export ValUniqueNo=$ValUniqueNo
}

echo k1=`FnGenerateUniqueNo`
echo k2=`FnGenerateUniqueNo`

kindly consider the above script.
it is required that when the function is called value of ValUniqueNo should be incremented.

Can any body help me...

You have to have persistent storage - a file, a database table, etc. Oracle sequences are stored along with other metadata like the schema on disk.

Try using a file. But. If this is for multiple processes with simultaneous access, then you have to use some sort of resource locking mechanism - a file lock might be an option. See either man flock or maybe man ioctl