RU/2: Форум. Общение пользователей и разработчиков OS/2 (eCS). : ERRORLVEL is a part of DOS conventions


Список сообщений | Написать новое | Ответить на сообщение | Домой Поиск:
Предыдущее сообщение | Следующее сообщение
From : GA
To : Roman Popov
Subj : ERRORLVEL is a part of DOS conventions
Thare are two books for this handling. A generel and best source for error handling in REXX is

Charles Daney, Programming in REXX,
McGraw-Hill, 1992, ISBN 0-07-015305-1

and a special issue for exact handling the ERRORLEVEL conditions is

Ronny Richardson, OS/2 Batch Files to Go, McGraw-Hill, 1994, ISBN 0070523703(paper) or 007052369X(hard)

Both publications one can bay on ebay or abebooks.com after looking a while.

Richardson writes:(Chapter 15 Errorlevel p.123-127)

While a nice place for batch files, the environment(ENV) is a very inhospitable place for programs to store information so they can communicate with each other. Each program
is provided with a copy of the ENV when it's first loaded.

When a program reads from or writes to the ENV, it's dealing with a copy of the
ENV and not with the original. When a program terminates, its copy of the ENV - along
with all teh changes the progarm made to it - are destroyed.

The errorlevel (ERLV) value (also called a return code [of the batch program,GA] is
provided to overcome this problem. The ERLV is a single byte of memory that can contain
only a single character. Normally, the content of ERLV is referred to as an ASCII value
rather than a chracter representation. ASCII values 0-255 are therefore possible.

How the ERLV works

When a program terminates, it can store a number in the ERLV to indicate its status at
termination. When a program use the ERLV, thge usual rule is to set it to zero for a successful execution and to higher values for diffrent types of errors.

The ERLV isn't stored in the ENV, so changes made to it aren't lost when a progarm terminates. Unlike the ENV, there's one one copy of the ERLV per session, and every program in a single session changes the same one. However, each different OS/2 session
has its own unique ERLV slot.

The ERLV doesn't change unless a program chenges it, you start another program, or you
reboot, so you can perform multiple test on it. However, the ERLV is automatically reset
to zero by OS/2 each time you start a new program, so each time a program runs, the
prior ERLV value is lost.

Under OS/2 you can reset the ERLV by running an internal command. This is not the case
under DOS and a few batch files migth not work properly as a result.

!!

Under OS/2, internal commands reset the ERLV to zero. This is not the case under DOS. As
a result, some batch files trnslated from DOS might need to be modified.

You don't need the ERLV when running programs from the command line because you'll see any error messages. However, a batch file file won't "see" an error message, so the
ERLV gives it a way to respond to errors.

OS/2 Errorlevel report

OS/2 has eleven(11) commands that are documented to support the ERLV. They are BACKUP, CHKDSK, COMP, EAUTIL, FORMAT, GRAFTABL, RECOVER, REPLACE, RESTORE, UNAPCK, and XCOPY. [I will list only one part XCOPY. When another part is wanted, write it, GA]

ERVL Meaning

0 Normal completion
1 No files found to XCOPY
2 Some files or directories weren't completed
3 Ended by the user
4 Ended beacuse of an errror

OS/2 ha also a number of internal commands with undocumented ERLV supports. For example, the DIR command returns an ERLV of one if you use an invalid switch and an
ERLV of 18 if tit doesn't find the file you specify after the DIR command. ....

To help you to experiment with the ERLV, os/2 includes a nice feature. Include a $R in
your prompt and your prompt will include the ERLV for the last command you issued.
Additionally, I've included a REXX programm called GET-ONE.CMD on the disk. This program
will take a single keystroke from the user and store its ASCII value in the ERLV. To turn
it from a batch file, use the command CALL GET-ONE and make sure teh program is either
in the current subdirectory or is in your path.

Of course , it can also be run from the command line without the CALL command.

/* Name: GET-ONE.CMD */
/* PURPOSE: REXX Program To Get A Single Character From User */
/* VERSION: 1.00 */
/* DATE: May 30, 1993 */

CALL RxFuncAdd 'SysGetKey', 'RexxUtil', 'SysGetKey'
SAY "Enter A Single Character"
Character = SysGetKey(echo)
ASCII = C2D(Character)
Exit ASCII







Sun 09 Feb 2003 17:20 Mozilla/4.61 [en] (OS/2; U)



Programmed by Dmitri Maximovich, Dmitry I. Platonoff, Eugen Kuleshov.
25.09.99 (c) 1999, RU/2. All rights reserved.
Rewritten by Dmitry Ban. All rights ignored.