There are two basic reasons errors occur when REXX is processing a procedure.
One reason is because of the way the procedure is written; for example, unmatched quotation marks or commas in the wrong place. Maybe an IF instruction was entered without a matching THEN. When such an error occurs, a REXX error message is issued.
A second reason for an error to occur is because of an OS/2 command that the REXX procedure has issued. For example, a COPY command can fail because the user's disk is full or a file cannot be found. In this case, a regular OS/2 error message is issued. When you write commands in your procedures, consider what might happen if the command fails to run correctly.
When a command is issued from a REXX procedure, the command interpreter gets a return code and stores it in the REXX special variable, RC (return code). When you write a procedure, you can test for these variables to see what happens when the command is issued.
Here is how you discover a failure. When commands finish running, they always provide a return code. A return code of 0 nearly always means that all is well. Any other number usually means that something is wrong. If the command worked normally (the return code was 0), you see the command prompt:
[C:\]
and you return to the screen you ran your program from in Presentation Manager, or in the PMREXX applicationReference you see printed under the last line of the procedure,
The REXX procedure has ended.
In the following example, ADD.CMD, there is an error in line 6; the plus sign (+) has been typed incorrectly as an ampersand (&).
/* This procedure adds two numbers */ SAY "Enter the first number." PULL num1 SAY "Enter the second number." PULL num2 SAY "The sum of the two numbers is" num1 & num2 EXIT
When the above procedure, ADD.CMD, is run, the following error message is displayed.
6+++ SAY "The sum of the two numbers is" num1 & num2 REX0034: Error 34 running C:\REXX\ADD.CMD,line 6:logical value not 0 or 1
To get help on the error message, type:
HELP REX0034
When help is requested, an error message such as the following is displayed:
REX0034 ***Logical Value not 0 or 1***
Explanation: The expression in an IF, WHEN, DO WHILE, or DO UNTIL
phrase must result in a '0' or a '1', as must any
term operated on by a logical operator.
Any command that is valid at the command prompt is valid in a REXX procedure. The command interpreter treats the command statement the same way as any other expression, substituting the values of variables, and so on. (The rules are the same as for commands entered at the command prompt.)
Return Codes: When the command interpreter has issued a command and the operating system has finished running it, the command interpreter gets the return code and stores it in the REXX special variable RC (return code). In your procedure, you should test this variable to see what happens when the command is run.
The following example shows a few lines from a procedure where the return code is tested:
/* Testing the Return Code in a Procedure. */ 'COPY a:*.lst b:' IF rc = 0 /* RC contains the return code from the COPY command */ THEN SAY 'All *lst files copied' ELSE SAY 'Error occurred copying files'