IBM-supplied commands have many parameters that can accept a wide variety of values. This design allows you to operate and program the system with a fraction of the total number of commands you would need if each individual task required a separate command.
A few commands have no parameters because they do not need any additional information to do their jobs. A good example is Change Password (CHGPWD). When you run the CHGPWD command, the system responds with a panel that allows you to type current and new passwords. No parameters are needed for CHGPWD to know how to do its job.
Most commands, however, do require additional information. The Display Data Area (DSPDTAARA) command, for example, needs to know which data area you want to display. If you run DSPDTAARA without supplying a parameter, expect the system to respond with a message telling you that more information is required.
Every command parameter has a name, also called a keyword. Keywords follow a convention much like the one commands follow. That is, keywords are made up of standard abbreviations. The Change System Value (CHGSYSVAL) command has two parameters, identified by the keywords SYSVAL and VALUE. The SYSVAL parameter identifies the system value to be changed. The VALUE keyword indicates the new value to be given to the system value.
CHGSYSVAL SYSVAL(QSTRUPPGM) VALUE('IPLPGM MYLIB')
Notice the convention that CL uses. The keyword is immediately followed by an open parenthesis. After the open parenthesis, key the parameter value and a close parenthesis. You may leave spaces after the open parenthesis and the parameter value.
Some parameters can be entered positionally. That is, you do not have to type the keywords, but you must enter them in the correct order:
CHGSYSVAL QSTRUPPGM 'IPLPGM MYLIB'