REXX- Variables, SAY and PULL

REXX variables are typeless: a variable can hold a string one moment and a number the next, and you never declare anything. Input and output are equally simple - SAY writes a line, PULL reads a line, and ARG picks up the parameters passed to your exec. This page covers all three with runnable examples.

Variables are typeless

• A variable comes into existence the moment you assign to it. No declarations, no types.
• The same variable can hold text and then a number: name = 'HOPPER' followed later by name = 42 is perfectly legal.
• Variable names are folded to uppercase, so Name, NAME and name are the same variable.
• Quoted text is a literal string; unquoted text is a variable name (or a REXX keyword).

• Placing values next to each other with a blank joins them with a single blank - this is called blank concatenation.
• The || operator joins with no blank: 'AB' || 'CD' gives ABCD.
• Arithmetic operators: + - * / plus % (integer divide), // (remainder) and ** (power).

Assignment and uppercase folding

• Because unquoted symbols fold to uppercase, city = 'Paris' stores the literal Paris (case preserved inside quotes) into variable CITY.
• But city = Paris (no quotes) copies the value of variable PARIS into CITY - and if PARIS was never assigned, CITY gets the string PARIS.
• Rule of thumb: quote every literal string, always.
• An unassigned variable used in an expression evaluates to its own name in uppercase - REXX calls this the NOVALUE condition, which you can trap with SIGNAL ON NOVALUE.

SAY - writing output

• SAY expression evaluates the expression and writes one line to the terminal.
• In batch, SAY output goes to the SYSTSPRT DD of the IRXJCL step.
• You can SAY variables, literals, function results, and arithmetic in any combination.

PULL - reading input

• PULL variable reads one line from the terminal (or from the data stack, if the stack is not empty).
• Important: PULL translates the input to uppercase. To preserve the typed case, use PARSE PULL variable instead.
• In batch, PULL reads lines from SYSTSIN.
• You can PULL several variables at once - the line is split into words, one per variable.

ARG - reading exec parameters

• ARG var1 var2 picks up the parameters passed to the exec, split into words.
• Run it like this: EX 'HLQ.REXX.EXEC(CHKDISK)' 'HLQ.MY.DATA' EXEC - the quoted string after the member name is the argument.
• Like PULL, plain ARG uppercases the input. Use PARSE ARG var to keep the original case (dataset names are usually uppercase anyway, so plain ARG is fine for them).
• In batch, pass parameters through PARM: PARM='HELLO HLQ.MY.DATA' - the member name comes first, then a blank, then your arguments.

Compound variables (stems)

• A stem is a variable name ending in a period, used like an array: emp.1, emp.2, and so on.
• By convention, stem.0 holds the count of elements.
• You can give the whole stem a default value: emp. = 'UNKNOWN' makes every unset element return UNKNOWN instead of its own name.
• DROP removes a variable or a whole stem: DROP emp.