IF - conditional execution of statements.

$*$IF

may take several forms. In the form

$*$IF expression : statement

the expression is evaluated and if the result is true (non-zero), EXEC executes the statement following the colon. This statement may be a TSS command or EXEC directive. The form

$*$IF expression : statement1
$*$ELSE : statement2

is similar. If the expression is non-zero, EXEC executes "statement1"; otherwise it executes "statement2". The colon ":" after $*$ELSE may be omitted.

$*$IF expression1 : statement1
$*$ELseIF expression2 : statement2
$*$ELSE : statement3

is yet another form. If "expression1" is non-zero, EXEC executes "statement1". Otherwise, if "expression2" is non-zero, EXEC executes "statement2". Otherwise, EXEC executes "statement3". Any number of $*$ELseIF statements may appear between the $*$IF and the $*$ELSE. Again, the ":" after $*$ELSE may be omitted.

$*$IF expression
   statements
$*$ELseIF expression
   statements
$*$ELseIF expression
   statements
      ...
$*$ELSE expression
   statements
$*$ENDif

lets you execute blocks of statements depending on the value of expressions. Statement blocks may contain $*$IF constructs of their own (nested IFs). See the section "Input Expansion" in the main explain file "expl exec" for more details that pertain to $*$IF statements.