Comment IEFBR14 (Score 5, Informative) 903
If by "program" you mean a stored program on what is conventionally meant by a computer today, I have a candidate. IEFBR14 was used on the earliest version of OS/360 in 1964 as a do-nothing program. It is still in use today, unchanged on the latest version of z/OS. Its function is to execute a JCL step which does nothing, but in the process of doing nothing, the job scheduler is invoked. This is one method of creating and deleting datasets (files). It is also the shortest valid OS/360 (and z/OS) program, containing two executable assembler statements and two assembler directives. The comments are mine.
IEFBR14 CSECT START PROGRAM SECTION
SR 15,15 SET EXIT CODE TO 0
BR 14 RETURN AND EXIT
END TELL ASSEMBLER END OF PROGRAM
Interestingly, the first version of this program had a bug, which was subsequently corrected by doubling the program length. It omitted the SR 15,15 statement, which meant that at program exit register 15 had an unpredictable value -- and the program exit code was therefore unpredictable. Since a zero exit code is used to guide the conditional execution of subsequent steps, a failure could be indicated when there was none.
And contrary to another post, I believe there are a lot of people with computer experience predating 1970 who read Slashdot. But I don't want to start a flame war over that.
IEFBR14 CSECT START PROGRAM SECTION
SR 15,15 SET EXIT CODE TO 0
BR 14 RETURN AND EXIT
END TELL ASSEMBLER END OF PROGRAM
Interestingly, the first version of this program had a bug, which was subsequently corrected by doubling the program length. It omitted the SR 15,15 statement, which meant that at program exit register 15 had an unpredictable value -- and the program exit code was therefore unpredictable. Since a zero exit code is used to guide the conditional execution of subsequent steps, a failure could be indicated when there was none.
And contrary to another post, I believe there are a lot of people with computer experience predating 1970 who read Slashdot. But I don't want to start a flame war over that.
