Regina Rexx 4.00 STREAM default changed to APPEND: making retry writes idempotent across interpreters

Direct answer

The Regina 4.00 STREAM default is not configurable per script. It is selected at interpreter startup, typically through a configuration file or environment variable, rather than through an in-language option. Because the setting is process-wide, a REXX script cannot change it with a directive inside the source file.

To make a retried LINEOUT idempotent across interpreters, do not rely on the default at all. Open the stream with an explicit mode argument every time, and keep that stream open across the retry loop.

There is no standard built-in function to query the active default mode at runtime. VERSION() identifies the interpreter and version, but it does not report the configured STREAM default. Runtime detection would require reading an external configuration file or environment variable whose name varies by distribution, which is fragile and non-portable.

Likely explanation vs. confirmed behavior

The duplication or overwrite you observe is most likely caused by the retry loop re-executing LINEOUT against a stream that was opened implicitly under the interpreter default. On Regina 4.00, if the default is APPEND, a retry adds a second copy of the line. On IBM Object REXX, if the default is REPLACE, the retry overwrites the file with the same line, leaving only one copy but discarding any prior content.

What is well-established is that the STREAM command accepts an explicit mode keyword and that the mode in effect when the stream is opened governs subsequent LINEOUT writes until the stream is closed or reopened. What remains uncertain without checking your specific Regina 4.00 distribution is the exact name and location of the startup configuration file or environment variable that controls the default. Verify that against your platform’s documentation.

Portable retry pattern

1. Before the first write, explicitly set the mode. If the script is appending to an existing log or data file, use:

   STREAM myfile, 'APPEND'

2. Perform the LINEOUT inside the retry loop without closing the stream. Because the mode was fixed at open time, every retry behaves identically regardless of the interpreter default.
3. If the first write must replace prior content, open once in REPLACE, write the initial line, close the stream, then reopen in APPEND for all retries:

   STREAM myfile, 'REPLACE'
   LINEOUT myfile, firstLine
   STREAM myfile, 'CLOSE'
   STREAM myfile, 'APPEND'
   /* retry loop here */

Verification

Test the pattern with a minimal script that writes a known line, forces a simulated failure, retries, and then inspects the file on both Regina 4.00 and IBM Object REXX.

/* test-retry.rexx */
fname = 'test.out'
STREAM fname, 'APPEND'
do i = 1 to 2
  if i = 1 then do
    say 'simulating failure'
    iterate
  end
  LINEOUT fname, 'retry line'
end
STREAM fname, 'CLOSE'

Run the script twice on each interpreter and confirm that the file contains the expected number of lines. If duplication still occurs, the stream was likely reopened inside the loop under the default mode rather than being held open under the explicit mode.

Because the exact Regina configuration mechanism varies by build, treat any claim about a specific environment variable name as unverified until you confirm it in your installation.