What is the DATALINES statement used for in a data step?

The DATALINES statement is used specifically to read instream data directly within a data step. When you include the DATALINES statement, you can enter data for the dataset inline without needing to reference an external file. This is particularly useful for small data sets or for testing purposes, allowing you to quickly input data directly within your SAS program.

When you use DATALINES, you follow it with the actual data records, which are read until a specific terminator, often a semicolon, is encountered. This facilitates the immediate use of data without additional file handling processes, thus streamlining the workflow for data entry tasks.

The other options refer to different functionalities within SAS. Defining column headers typically involves specific data step options or other statements such as INPUT, while validating data types is generally managed through other data step logic or procedures. Writing data to an external file is handled by specific procedures like PROC EXPORT or statements like FILE, rather than through the DATALINES statement.