Catch Exception Calling "executenonquery"

I have a Powershell script that inserts a primary key value and another value into a SQL Server 2012 database. This is the INSERT SQL string that includes IF NOT EXISTS, where $sql

Solution 1:

$SQL_UPDATE = "BEGIN
                  IF NOT EXISTS (SELECT 1
                                 FROM dbo.Download
                                 WHERE Date_of_Download = CAST(GETDATE() AS DATE))
                  BEGIN
                      INSERT INTO dbo.Download (Date_of_Download , OtherColumnName)
                      VALUES (CAST(GETDATE() AS DATE) ,$sql_output)
                  END
              END"