Opening files

The default mode for opening files in REXX is READ/WRITE (even if you open 
the file implicitly via the <LINEIN function!). This prevents other 
programs from opening the file even if the program that opens this file 
first only wants to read from the file. 

To avoid being locked out of a file like this, I suggest you use an 
explicit call of the function <STREAM to open a file in READ mode, if you 
only want to read from it.