20. Writing 4GL Statements : Call Statements : Using the Call System Statement
 
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Using the Call System Statement
Use the call system statement to call the operating system (and, optionally, to run a system program) from within an application. If you do not specify a command as a parameter in the call system statement, the application user enters the operating system level and sees the operating system prompt. If you specify a particular command, Ingres executes that command, then returns to the running application.
The example below calls the operating system without specifying a command:
call system;
This places the user at the operating system level. You can execute any command provided by the operating system. When you exit from the system, control returns to the current frame in the application.
The example below calls the system and executes the program called expenses, after which control returns to the current frame in the application:
call system 'expenses';
Do not use this call to start up a new Ingres application, because the Data Manager connection is started, which uses up system resources. Instead, use the call application statement where possible.
VMS: Do not use the VMS inquire command in a command file called with call system. For example the statement shown below does not execute properly:
$ inquire x "Enter data:  "   /* error */
The recommended alternative is as follows:
$ open/read userterm tt
$ read/prompt="Enter data: " userterm varname
$ ...
$ close userterm