Varying the input or output file at run time
The file-name that you code in a SELECT clause
is used as a constant throughout your COBOL program, but you can associate
the name of that file with a different system file at run time.
About this task
Changing a file-name within a COBOL program would require
changing the input statements and output statements and recompiling
the program. Alternatively, you can change the DSNAME value
in the DD statement or
the DSN or PATH value in the export command
to use a different file at run time.
Environment variable
values that are in effect at the time of the OPEN statement
are used for associating COBOL file-names to the system file-names
(including any path specifications).
The name that you use in the assignment-name of
the ASSIGN clause must be the same as the ddname
in the DD statement or the environment variable
in the export command.
The file-name that
you use in the SELECT clause (such as SELECT
MAINFILE) must be the same as in the FD file-name entry.
Two files should not use the same ddname or environment
variable name in their SELECT clauses; otherwise,
results could be unpredictable. For example, if DISPLAY output
is directed to SYSOUT, do not use SYSOUT as
the ddname or environment variable name in the SELECT clause
for a file.