Originally posted by: BasilTK

There are three ways for a user to set the filsystem when using COBOL for AIX:

1) export COBRTOPT="fs=<filesys>" . This is a global setting and will be applied to all your files and programs. 
eg
export COBRTOPT="fs=stl"

or

2) Filenames in environment variables, such as: export INFILE="<filesys>-<filename>" - it specifies which file system to use, and provides the filename for that specific file only.
eg:
export INFILE="stl-/home/username/inputfilename"     or
export OUTFILE="stl-/home/username/outputfilename" 
 
     Please note if you use export INFILE="<filename>" - which does not specify a file system, it means that you are actually using whatever was established via export COBRTOPT="fs=<filesys>" (see number 1 above). 
 

or
3) ASSIGN statements in the COBOL source. One can provide a hard coded filename, or filesystem-filename in the program (which is fairly rare).   Again, if there is no filesystem specified, then it means that you COBOL environment defaults to COBRTOPT="fs=<filesys>"

eg:

    file-control.
           select outfile assign to "STL-outfile.txt"
           organization is sequential.