Step-by-Step Programming with Base SAS 9.4, Second Edition, 2nd Edition

Prerequisites

You should understand the concepts that are presented in the following sections:

• Chapter 3, “Introduction to DATA Step Processing,” on page 27

• Chapter 4, “Starting with Raw Data: The Basics,” on page 51

• Chapter 7, “Understanding DATA Step Processing,” on page 107

• Chapter 23, “Analyzing Your SAS Session with the SAS Log,” on page 365

Understanding How the SAS Supervisor Checks a

Job

To better understand the errors that you make so that you can avoid them in the future, it

is important to understand how the SAS Supervisor checks a job. The SAS Supervisor is

the part of SAS that is responsible for executing SAS programs. To check the syntax of a

SAS program, the SAS Supervisor does the following:

• reads the SAS statements and data

• translates the program statements into executable machine code or intermediate code

• creates data sets

• calls SAS procedures, as requested

• writes error messages

• ends the job

The SAS Supervisor knows the following information about DATA and PROC steps:

• the forms and types of statements that can be present in a DATA step

• the types of statements and the options that can be present in a PROC step

To process a program, the SAS Supervisor scans all the SAS statements and breaks each

statement into words. Each word is processed separately. When all the words in a step

are processed, the step is executed. If the SAS Supervisor detects an error, then it flags

the error at its location and writes an explanation in the log. The SAS Supervisor

assumes that anything that it does not recognize is an error.

Understanding How SAS Processes Errors

When SAS detects an error, it usually underlines the error in the log or underlines the

point at which it detects the error, identifying the error with a number. Each number is

uniquely associated with an error message. Then SAS enters syntax check mode, and

reads the remaining program statements, checks their syntax, and underlines additional

errors if necessary.

In a batch or noninteractive program, an error in a DATA step statement causes SAS to

remain in syntax check mode for the rest of the program. It does not execute any more

DATA or PROC steps that create external files or SAS data sets. Procedures that are read

from SAS data sets execute with 0 observations, and procedures that do not read SAS

400 Chapter 25 • Diagnosing and Avoiding Errors