Running Windows or MS-DOS Commands from within SAS

You can execute Windows or MS-DOS commands from within SAS by using the X statement or the X command. You can also use the CALL SYSTEM statement or the SYSTASK statement from within a DATA step. Windows or MS-DOS commands can be issued either asynchronously or synchronously. When you run a command as an asynchronous task, the command executes independently of all other tasks that are currently running. When you run a command as a synchronous task, the command must complete before another task can run.

To issue a command asynchronously, use either the SYSTASK statement with the NOWAIT option or specify the NOXSYNC system option. To issue a command synchronously, use either the SYSTASK statement with the WAIT option or specify the XSYNC system option. For more information about running asynchronous commands using the SYSTASK statement, see SYSTASK Statement: Windows.

You can use the X statement or the X command to run Windows commands. The X statement can be run outside of a DATA step. You can enter the X command in the command bar or any SAS command line.

The X statement is similar to the X command in the SAS windowing environment. The major difference between the two is that the X statement is submitted like any SAS statement. However, the X command is issued as a windowing environment command. This section uses the X statement in its examples, but the information applies to the X command as well.

When you submit the X statement that you exit your SAS session temporarily and gain access to the Windows command processor. The X statement has the following syntax:

The optional command argument is used either to issue an operating system command or to invoke a Windows application such as Notepad. This discussion concentrates on using the X statement to issue operating system commands. However, you should be aware that the X statement can also be used to invoke Windows applications.

If you want to run only one operating system command, include the command as an argument to the X statement. When you submit the X statement, the command is executed, and you cannot issue any additional commands.

If you want to run several operating system commands, submit the X statement without an argument. A command prompt appears where you can issue an unlimited number of operating system commands. Remember, any environment variables that you define are not available to SAS. If you submit an X statement or command without an argument command, type EXIT to return to your SAS session.

The X command is a global SAS statement. Therefore, it is important to realize that you cannot conditionally execute the X command. For example, if you submit the following code, the X statement is executed:

data _null_;
   answer='n';
   if upcase(answer)='y' then
      do;
         x 'md c:\extra';
      end;
run;

In this case, the C:\EXTRA folder is created regardless of whether the value of ANSWER is equal to 'n' or 'y'.

If you want to issue operating system commands conditionally, use the CALL SYSTEM routine, as in the following example:

options noxwait;
data _null_;
   input flag $ name $8.;
   if upcase(flag)='Y' then
      do;
         command='md c:\'||name;
         call system(command);
      end;
   datalines;
Y mydir
Y junk2
N mydir2
Y xyz
;

This example uses the value of the variable FLAG to conditionally create folders. After the DATA step executes, three folders have been created: C:\MYDIR, C:\JUNK2, and C:\XYZ. The C:\MYDIR2 folder is not created because the value of FLAG for that observation is not Y.

For more information about the CALL SYSTEM routine, see CALL SYSTEM Routine: Windows and the section on the CALL SYSTEM routine in SAS System Options: Reference.

The XWAIT system option controls whether you have to type EXIT to return to your SAS session after an X statement or X command has finished executing an MS-DOS command. (The XWAIT system option is not used if an X statement is issued without a command argument or if the X statement invokes a Windows application such as Notepad.) This option and its negative form operate in the following ways: If you issue an X statement or X command without a command argument, you must type EXIT to return to your SAS session, even if NOXWAIT is in effect.

When a window created by an X statement is active, reactivating SAS without exiting from the command processor causes SAS to issue a message box containing the following message:

   The X command is active. Enter EXIT at
   the prompt in the X command window to
   reactivate this SAS session.

If you receive this message box, click Command Prompt on the Windows Task Bar. Enter the EXIT command from the prompt to close the window and return to your SAS session.

The XSYNC system option specifies whether the operating system command that you submit executes synchronously or asynchronously with your SAS session. This option and its negative form operate in the following ways:

Specifying NOXSYNC can be useful if you are starting applications such as Notepad or Excel from your SAS session. For example, suppose you submit the following X statement:

x notepad;

If XSYNC is in effect, you cannot return to your SAS session until you close the Notepad. But if NOXSYNC is in effect, you can switch back and forth between your SAS session and the Notepad. The NOXSYNC option breaks any ties between your SAS session and the other application. You can even end your SAS session; the other application stays open until you close it.

The XWAIT and XSYNC system options have very different effects. An easy way to remember the difference is the following:

The various option combinations are summarized in Combining the XWAIT and XSYNC System Options.