.FILE EXISTS 
This subroutine is called to check if a file exists in the filesystem.
  Usage: 
      PASS         <exists?>                  FIELD            SHARE? Y
      PASS         <pathname>                 FIELD            SHARE? N
      GOSUB    --- .FILE EXISTS
      *        check for errors
      IF       --- .FILE EXISTS               NE
  Description: 
This subroutine is called to check if a file exists in the filesystem. Both parameters are required, the subroutine will CANCEL if they are not received.
<exists?> is the result, indicating if file exists or not (Required). This must be PASSed with Share "Y". Returns Y if the file exists, N if not.
<pathname> is pathname to test (Required).
Notes:
The subroutine tries to open the file for Read access, and if it cannot, it returns a "N". It cannot distinguish between a file that does not exist and a file it cannot open due to file permissions, both cases will return "N".
You can also use this to test if a directory exists by passing a directory name (Unix/Linux only).
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-- 
PeteBrower - 2011-08-12