.CBL File Extension
What is a CBL file?
Source code file written in COBOL (COmmon Business-Oriented Language), one of the oldest programming languages still in use; often used for writing programs for business, accounting, and administration; must be compiled by a COBOL compiler for the target system before run.
Several different standards for COBOL exist, beginning with COBOL-68 and including COBOL-74, COBOL-85, and COBOL 2002. Therefore, you should make sure your text editor and compiler support the appropriate version of COBOL you're using.