Host Environment Commands › REXX Instructions Against Host Commands

REXX Instructions Against Host Commands

In OPS/REXX, instructions provide logic structures (IF ... THEN ... ELSE ..., DO WHILE ... END) and define variables, while host commands allow you to issue actions (TSO commands, ISPEXEC commands, z/OS operator commands, JES commands, and VM/CP commands). In general, when OPS/REXX encounters an instruction consisting solely of an expression (a string by itself is a valid expression), it assumes that the instruction is a host command.

OPS/REXX does not interpret the syntax of host commands. To OPS/REXX, a host command is a meaningless string of characters. For instance, if you make a coding mistake such as placing an OPS/REXX function on a line by itself without a variable and an equal sign, OPS/REXX will probably interpret it as a host command and send it to the environment specified in the last ADDRESS statement. Conversely, instructions have a specific meaning to OPS/REXX.

Examples: OPS/REXX Instructions and Host Commands

OPS/REXX program demonstrating instructions and host commands:

if today = "Friday" then
  say "TGIF !!!"
else
  do
    address OPER "D A,L"
    address TSO "LISTBC"
  end

In the above example, the strings D A,L and LISTBC are host commands. All other constructs are OPS/REXX instructions. The specific instructions are:

• if ... then ... else ...
• say ...
• do ... end
• address ...

The data structures shown are:

• Variables (today)
• String constants (“Friday”, “TGIF !!!”, “OPER”, “D A,L”, “TSO”, and “LISTBC”)
• Expressions (today = “Friday”)