$IFELSE
: Two-way conditional
The syntax of this built-in primitive is $IFELSE(
expr1,
expr2,
action-if-equal,
action-if-not-equal)
. The
expansions of expr1 and expr2 are compared on a byte-by-byte
basis. If they are equal, the first action is taken, otherwise the
second action is taken.
For example,
$M(S="abc")@% $IFELSE("abc", S, yes, no)
evaluates to yes
.