PIPE mode in external file functions

To get the output of shell command within SAS, we have to resort to PIPE.
Generally the job is using DATA step input/output.
We can also use external file funcitons to handle it, although it is more complex.

%let command = hostname;

data _null_;
 length value $ 20;
 rc = filename('myfile', "&command", 'PIPE');
 fid = fopen('myfile', 'S');
 rc = fread(fid);
 rc = fget(fid, value, 20);
 rc = fclose(fid);
 rc = filename('myfile'); 

 put "Command output:" value;
run;

%let filerf=myfile;
%let rc = %sysfunc(filename(filerf, &command, pipe));
%let fid = %sysfunc(fopen(&filerf, S));
%let rc = %sysfunc(fread(&fid));
%let rc = %sysfunc(fget(&fid, value, 20));
%let rc = %sysfunc(fclose(&fid));
%let rc = %sysfunc(filename(filerf));

%put Command output: &value;

a special function for %sysfunc world: filename function

Below are the code from SAS online doc:
%let filrf=myfile;
%let rc=%sysfunc(filename(filrf, physical-filename));
%if &rc ne 0 %then
%put %sysfunc(sysmsg());
%let rc=%sysfunc(filename(filrf));

It should be noted that the fileref is "myfile", not "filerf". That means the macro variable "filerf" contains the ACTUAL fileref.
When the macro variable does not exist, the system generates a fileref automatically.

It seems that it is unique to filename function.
For now, I have not found any other functions which can take the similar behavior.

Note that it will not work if the fileref has been assigned. For more information, please see http://support.sas.com/kb/6/567.html