Hercules is an open-source software implementation of the mainframe System/370 and ESA/390 architectures, in addition to the latest 64-bit z/Architecture. Hercules runs under Linux, Windows, Solaris, FreeBSD, and Mac OS X.
A user can connect to a mainframe server in a number of ways such a thin client, dummy terminal, Virtual Client System (VCS), or Virtual Desktop System (VDS). Every valid user is given a login id to enter into the Z/OS interface (TSO/E or ISPF).
Compiling COBOL Programs
In order to execute a COBOL program in batch mode using JCL, the program needs to be compiled, and a load module is created with all the sub-programs. The JCL uses the load module and not the actual program at the time of execution. The load libraries are concatenated and given to the JCL at the time of execution using JCLLIB or STEPLIB.
There are many mainframe compiler utilities available to compile a COBOL program. Some corporate companies use Change Management tools like Endevor, which compiles and stores every version of the program. This is useful in tracking the changes made to the program.
IGYCRCTL is an IBM COBOL compiler utility. The compiler options are passed using the PARM parameter. In the above example, RMODE instructs the compiler to use relative addressing mode in the program. The COBOL program is passed using the SYSIN parameter. Copybook is the library used by the program in SYSLIB.
Executing COBOL Programs
Give below is a JCL example where the program MYPROG is executed using the input file MYDATA.URMI.INPUT and produces two output files written to the spool.
The load module of MYPROG is located in MYDATA.URMI.LOADLIB. This is important to note that the above JCL can be used for a non-DB2 COBOL module only.
Executing COBOL-DB2 programs
For running a COBOL-DB2 program, a specialized IBM utility is used in the JCL and the program; DB2 region and required parameters are passed as input to the utility.
The steps followed in running a COBOL-DB2 program are as follows:
When a COBOL-DB2 program is compiled, a DBRM (Database Request Module) is created along with the load module. The DBRM contains the SQL statements of the COBOL programs with its syntax checked to be correct.
The DBRM is bound to the DB2 region (environment) in which the COBOL will run. This can be done using the IKJEFT01 utility in a JCL.
After the bind step, the COBOL-DB2 program is run using IKJEFT01 (again) with the load library and the DBRM library as the input to the JCL.
In the above example, MYCOBB is the COBOL-DB2 program run using IKJEFT01. Please note that the program name, DB2 Sub-System Id (SSID), and DB2 Plan name are passed within the SYSTSIN DD statement. The DBRM library is specified in the STEPLIB.