VX/DCL – OpenVMS DCL

Dispatch model

Every command line resolves to a verb handler through dcl_dispatch(). It first consults small state-specific tables (for IF / THEN / ELSE and SUBROUTINE handling while in a GOTO or CALL branch), then the master verb table, and finally falls back to loading a routine from a dynamic shared image. Every handler shares the signature U32 DO_xxx(U32) and returns a VMS-style status code, so success is tested the VMS way: odd status is success.

External utility images

File and data utilities are built as standalone executables and also compile into the interpreter when a smaller footprint is wanted. The standalone image set includes:

Symbols, logical names and substitution

Local and global symbols, logical-name tables, and the full VMS substitution rules are implemented in the interpreter's per-process control block. The procedure below is a representative end-of-day batch job for a funds-transfer system: it sets a symbol and a logical name, tests for a file with the F$SEARCH lexical, sorts a ledger through VX/SORT, and queues a follow-on procedure through VX/JSP.

$! nightly_close.com - end-of-day batch for the funds-transfer system
$
$ SET NOON
$ ACCT_DIR :== SYS$LOGIN:[BANKING.ACCOUNTS]
$ DEFINE ACCT$DATA DUA0:[BANKING.DATA]
$
$ start_time = F$TIME()
$ WRITE SYS$OUTPUT "Close started at ''start_time'"
$
$ IF F$SEARCH("ACCT$DATA:LEDGER.DAT") .EQS. ""
$ THEN
$     WRITE SYS$OUTPUT "No ledger to process - exiting"
$     EXIT
$ ENDIF
$
$ SORT/KEY=(POSITION:1,SIZE:12) ACCT$DATA:LEDGER.DAT LEDGER_SORTED.DAT
$ SUBMIT/QUEUE=SYS$BATCH ACCT_DIR:POST_STATEMENTS.COM
$ EXIT

Nested single and double quotes substitute symbols and lexical results into the command line before it is parsed, exactly as on VMS. Foreign commands (a symbol assigned to an image plus arguments) dispatch through the same path, so tools invoked by name from a procedure continue to work.

Built-in verbs by category

VX/DCL implements more than 120 distinct built-in verbs (195 dispatch entries once the SET, SHOW and TCPIP sub-verbs are counted). They group into the same families as native DCL.

Essential commands

These commonly-migrated commands are implemented so command procedures and interactive use continue without modification.

Example: F$CVTIME and nested substitution

The procedure below exercises F$CVTIME and the nested double-quote substitution rules. It is representative of date-driven batch logic that migrates unchanged.

$ WRITE SYS$OUTPUT "  DATETIME ''F$CVTIME (,,""DATETIME"")'"
$ WRITE SYS$OUTPUT "      DATE ''F$CVTIME (,,""DATE"")'"
$ WRITE SYS$OUTPUT "      YEAR ''F$CVTIME (,,""YEAR"")'"
$ WRITE SYS$OUTPUT "   WEEKDAY ''F$CVTIME (,,""WEEKDAY"")'"
$ WRITE SYS$OUTPUT " DAYOFYEAR ''F$CVTIME (,,""DAYOFYEAR"")'"
$ WRITE SYS$OUTPUT " Yesterday ''F$CVTIME (""YESTERDAY"",""ABSOLUTE"",""DAYOFYEAR"")'"
$ EXIT

F$CVTIME supports the full VMS output field set (DATETIME, DATE, TIME, YEAR, MONTH, DAY, WEEKDAY, HOUR, MINUTE, SECOND, DAYOFYEAR and more) and the input keywords YESTERDAY, TODAY, TOMORROW and ABSOLUTE.

Path-translation lexicals

Four path-translation lexicals expose the runtime's path mapper directly to scripts. They are VX/DCL extensions, not present in native VMS DCL, and are the recommended way for a procedure to move between VMS and host path conventions when it needs an explicit conversion.

RMS file-spec parsing

VMS file specs are parsed through RMS extended attribute blocks, so device, directory, name, type, and version decomposition matches RMS behaviour. This is the same machinery that resolves LOGIN.COM at login and that backs the DUA0:[A.B.C]FILE.TXT mapping above, which keeps file handling in the file verbs (COPY, CREATE, APPEND, BACKUP, CONVERT, DIRECTORY) consistent with the rest of the runtime.

Example: the SORT verb calling VX/SORT

The DO_SORT handler shows the full VX/SORT lifecycle: feed each input file, begin the sort, run it, then always release the sort context. Every call is checked with the VMS convention that odd status is success.

while (nn < num_files) {
    vxrt_dsc64t(&d_infile, (U16)strlen(infile[nn]), infile[nn]); nn++;
    rc = SOR_D_PASS_FILES(&d_infile, &d_outfile, org);     // feed each input file
    if ((rc & 1) == 0) {
        fprintf(sysout, "DCL$SORT: SOR$PASS_FILES Error\r\n");
        VX_RETURNS(rc);
    }
    vxrt_dsc64t(&d_outfile, 0, NULL);                       // clear output for next pass
}
rc = SOR_D_BEGIN_SORT(key_info, &key_mrs, &key_options);    // start the sort
rc = SOR_D_SORT_MERGE();                                    // run it
SORT_END:;
rc = SOR_D_END_SORT();                                      // always release the sort context

Intentional divergences from native VMS DCL

A handful of behaviours differ from native DCL by design, so scripts can interoperate with a Linux or Windows host. Each divergence is additive: VMS syntax still behaves the VMS way.

Lexical functions (43)

Path-translation extensions

Verb categories

Key facts