Getsystemval?

[Thomson, Martyn EDUC:EX]

Hello Listers,
I'm trying to add a check to initialize procedure of a QUICK screen to check for the existence of a file using "RUN COMMAND", and testing $STATUS indirectly with GETSYSTEMVAL. Something like this - 

DEFINE t_SRB_FILES CHAR*10 = GETSYSTEMVAL("SRB_FILES",SYMBOL)

  RUN COMMAND "dir/sin/out=sys$login:srblist.tmp xtr$srb"
  RUN COMMAND "SRB_FILES == $STATUS"
  IF t_SRB_FILES = "%X00000001"
  THEN BEGIN
      WARNING = "ERROR: Cannot proceed: Vouchers posted to CAS already today" &
        NOW RESPONSE
      RETURN
  END

Although this works fine interactively in DCL the GETSYSTEMVAL returns an empty string. 
I've tried making it a TEMP and using LET t_SRB_FILES = GETSYSTEMVAL("SRB_FILES",SYMBOL)
 
I've tried using logicals - RUN COMMAND "DEFINE/GROUP SRB_FILES '$STATUS"  
                            LET t_SRB_FILES = GETSYSTEMVAL("SRB_FILES",LOGICAL,"(LNM$GROUP")

I've tried interrogating $STATUS directly - LET t_SRB_FILES = GETSYSTEMVAL("$STATUS",SYMBOL)
A value is returned but is the same irrespective of whether the file exists! Any ideas how to make this work?

Martyn Thomson
PowerHouse 7.10G1 on OpenVMS 8.3