COBOL by Example: Environment Variables
Reading operating system environment variables with ACCEPT FROM ENVIRONMENT, configuring programs dynamically based on runtime context, handling missing variables with space checks, and integrating with modern deployment scenarios for configuration.
Code
IDENTIFICATION DIVISION.
PROGRAM-ID. ENV-VARS.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 USER-NAME PIC X(20).
PROCEDURE DIVISION.
DISPLAY "Reading USERNAME from OS...".
ACCEPT USER-NAME FROM ENVIRONMENT "USERNAME".
IF USER-NAME = SPACES
DISPLAY "Variable not found."
ELSE
DISPLAY "Hello, " USER-NAME
END-IF.
STOP RUN.Explanation
COBOL programs often need to interact with their host operating system. The ACCEPT statement is used to retrieve data from outside the program. While it can read from the console (stdin), it is also used to read environment variables.
The syntax ACCEPT variable FROM ENVIRONMENT "VAR_NAME" allows the program to configure itself dynamically based on the runtime environment. This is essential for modern deployment scenarios, such as reading database connection strings, API keys, or user identities from the container or OS environment.
Always handle the case where the environment variable is missing. In standard COBOL, the behavior might vary (e.g., the variable remains unchanged or is filled with spaces), so explicit checks are recommended to ensure the program behaves predictably.