CHAPTER 3: The Windows Batch Interface

There are two commands you can use to execute Empress Query Language commands under the Windows NT command prompt:

1. empcmd to execute a single command.
2. empbatch to execute a batch of commands.

The Batch Interface allows rapid packaging of prototype database management interactions. It allows existing console programs, C routines, and other batch programs to be invoked by simple commands, thereby encouraging the rapid design and development of custom interfaces to the database management system.

The command empcmd is used to have the Windows NT command prompt execute one Empress SQL command. The syntax of the command is as follows:

empcmd database "command"

where:

Example 1: Retrieve an Attribute Values from a Table

The following command lists all employees from the personnel table in the database repairs:

   empcmd repairs "SELECT name FROM personnel"

The above command executes the Empress SQL command "SELECT name FROM personnel" on the database called repairs, without the need to invoke empsql directly. Once the command has been executed, control returns to the Windows NT command prompt.

The above empcmd command can also be stored in a batch file called names.bat. Once this is done, typing in names under the command prompt will produce the list of employee names as before.

Example 2: Passing Argument to the Batch File

The following command, stored in a batch file called phone.bat, produces the telephone number of the employee given as its argument.

   empcmd repairs "select phone from personnel dump
        where name = '%1'"<$Idump keyword>

The dump keyword has been included in the empcmd command to suppress printing the heading phone, which would be spurious information for this program.

To find Jones' phone number, type in:

   phone Jones

will get the following:

   667-2951

The command empbatch allows you to submit a batch of Empress commands from the operating system. The syntax of empatch is as follows:

empbatch database

where:

The command empbatch works in interactive mode. It is similar to being in Empress SQL but there are no prompts. A semicolon (;) is used to end each Query Language command, and a command may span several lines. The program exits on a syntax error.

For example, if you type in from the command prompt:

   empbatch repairs

the cursor will wait on the next line for a command. Typing in a command brings an immediate response:

   SELECT FROM loans WHERE name = "Jones";

will produce:

   names   date                amount

   Jones    7 February 1992    $33.95
   Jones    3 April 1992       $25.00
   Jones   12 August 1992     $300.00

<Ctrl+Z> or <F6> will return you to the command prompt.

To submit a series of Query Language commands from a file, use input redirection from the file or specify it as the optional input file. For example, you use a system editor to create a file called queries which contains:

   select from loans where name = "jones";
   select from loans where name = "mosca";

Then submit the queries by typing:

   empbatch repairs < queries

The input redirection makes the empbatch command get input from the file queries.