How to run SQL in shell script

#!/bin/ksh
variable1=$( 
echo "set feed off
set pages 0
select count(*) from table;
exit
"  | sqlplus -s username/password@oracle_instance
)
echo "found count = $variable1"

You can use a heredoc. e.g. from a prompt:

$ sqlplus -s username/password@oracle_instance <<EOF
set feed off
set pages 0
select count(*) from table;
exit
EOF

so sqlplus will consume everything up to the EOF marker as stdin.