IEFBR14: Программа-заглушка для мэйнфреймов IBM

"Do nothing" program on IBM mainframes
IEFBR14 is an IBM mainframe utility program. It runs in all IBM mainframe environments derived from OS/360, including z/OS. It is a placeholder that returns the exit status zero, similar to the true command on UNIX like systems.

On OS/360 and derived mainframe systems, most programs never specify files (usually called datasets) directly, but instead reference them indirectly through the Job Control Language (JCL) statements that invoke the programs. These data definition (or "DD") statements can include a "disposition" (DISP= ) parameter that indicates how the file is to be managed — whether a new file is to be created or an old one re used; and whether the file should be deleted upon completion or retained; etc. IEFBR14 was created because while DD statements can create or delete files easily, they cannot do so without a program to be run due to a certain peculiarity of the Job Management system, which always requires that the Initiator actually execute a program, even if that program is effectively a null statement. The program used in the JCL does not actually need to use the files to cause their creation or deletion — the DD DISP= specification does all the work. Thus a very simple do nothing program was needed to fill that role. IEFBR14 can thus be used to create or delete a data set using JCL.

At least on z/OS, branching off to execute another program would cause the calling program to be evaluated for syntax errors at that point.

The "IEF" derives from a convention on mainframe computers that programs supplied by IBM were grouped together by function or creator and that each group shared a three letter prefix. In OS/360, the first letter was almost always "I", and the programs produced by the Job Management group (including IEFBR14) all used the prefix "IEF". Other common prefixes included "IEB" for dataset utility programs, "IEH" for system utility programs, and "IEW" for program linkage and loading. Other major components were (and still are) "IEA" (Operating System Supervisor) and "IEC" (Input/Output Supervisor). As explained below, "BR 14" was the essential function of the program, to simply return to the operating system. This portion of a program name was often mnemonic — for example, IEBUPDTE was the dataset utility (IEB) that applied updates (UPDTE) to source code files, and IEHINITT was the system utility (IEH) that initialized (INIT) magnetic tape labels (T). As explained further in "Usage" below, the name "BR14" comes from the IBM assembler language instruction "Branch (to the address in) Register 14", which by convention is used to "return from a subroutine". Most early users of OS/360 were familiar with IBM Assembler Language and would have recognized this at once.