CLIST

CLIST (Command List) (pronounced "C-List") is a procedural programming language for TSO in MVS systems. It originated in OS/360 Release 20 and has assumed a secondary role since the availability of Rexx in TSO/E Version 2. The term CLIST is also used for command lists written by users of NetView.^[1]

In its basic form, a CLIST program (or "CLIST" for short) can take the form of a simple list of commands to be executed in strict sequence (like a DOS batch file (*.bat) file). However, CLIST also features If-Then-Else logic as well as loop constructs.

CLIST is an interpreted language. That is, the computer must translate a CLIST every time the program is executed. CLISTs therefore tend to be slower than programs written in compiled languages such as COBOL, FORTRAN, or PL/1. (A program written in a compiled language is translated once to create a "load module" or executable.)

CLIST can read/write MVS files and read/write from/to a TSO terminal. It can read parameters from the caller and also features a function to hold global variables and pass them between CLISTs. A CLIST can also call an MVS application program (written in COBOL or PL/I, for example). CLISTs can be run in background^[ii]^[iii]. CLISTs can display TSO I/O screens and menus by using ISPF dialog services.

Compare the function of CLIST with that provided by REXX.

Example programs

PROC 0 WRITE HELLO WORLD!

Adding If-Then-Else logic:

   /********************************************************************/    /*  MULTI-LINGUAL "HELLO WORLD" PROGRAM.                            */    /*                                                                  */    /*  THIS CLIST, STORED AS USERID.TSO.CLIST(TEST), CAN BE INVOKED    */    /*  FROM THE ISPF COMMAND LINE AS SHOWN IN THE FOLLOWING EXAMPLE:   */    /*                                                                  */    /*     COMMAND ===> TSO TEST SPANISH                                */    /*                                                                  */    /********************************************************************/    PROC 1 LANGUAGE      IF &LANGUAGE = SPANISH THEN +         WRITE HOLA, MUNDO      ELSE IF &LANGUAGE = FRENCH THEN +         WRITE BONJOUR, MONDE      ELSE +         WRITE HELLO, WORLD    EXIT

^[iv]

Footnotes

^ Usually IKJEFT01
^ by running JCL that executes a TSO terminal monitor program^[i] (TMP)
^ This capability was added by the program product Time Sharing Option/Extensions (TSO/E), which is a standard part of OS/390 and z/OS.
^ Here PROC is treated as a separate routine.