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> 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
> 
>     
> 
> 
> 
>

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