You can access regular operating system files and blocked special files by using sequential-access, direct-access, or stream-access methods.
You can only access pseudo-devices, pipes, and character special files by using sequential-access methods, or stream-access without using the POS= specifier.
When you link files together, you can use their names interchangeably, as shown in the following example:
OPEN (4, FILE="file1") OPEN (4, FILE="link_to_file1", PAD="NO") ! Modify connection
Do not specify the POSITION= specifier as REWIND or APPEND for pipes.
Do not specify ACTION='READWRITE' for a pipe.
Do not use the BACKSPACE statement on files that are pseudo-devices or character special files.
Do not use the REWIND statement on files that are
pseudo-devices or pipes.