@node Logical, Ltype, Location, Commands

@iftex
@syntax Logical.
@end iftex
@example
Syntax: Logical Operators
@end example
@pindex Logical operators

The following logical operators are allowed on vectors and scalars in
SM, where non-zero means true:


@example
Unary:

!expr           Logical Complement    
@end example

@example
Binary:

expr == expr    Equal to             expr != expr    Not equal
expr < expr     Less than            expr <= expr    Less than or equal
expr > expr     Greater than         expr >= expr    Greater than or equal
expr && expr    Logical and          expr || expr    Logical or
@end example

Only @code{!}, @code{==}, and @code{!=} are allowed for string valued vectors.
All arithmetic vectors test unequal to all string-valued vectors.

@findex string vectors, if tests
For string vectors, there are three cases to consider:
@code{vstr1 == vstr2} generates a vector of the same length as
@code{vstr1} (with must be the
same length as @code{vstr2}) by comparing the two vectors element by element;
@code{'str1' == vstr}
generates a vector of the same length as @code{vstr}
by comparing each element of the vector @code{vstr} to the string @code{str1};
and
@code{'str1' == 'str2'}
which returns a scalar by comparing the strings @code{str1} and @code{str2}
(so it's false in this example).

@findex precedence, logical operators
As in C, @code{==} has a higher precedence than @code{&&}, which in turn has
higher precedence than @code{||}.

Note that there is also a ternary operator, @code{(expr1) ? expr2 : expr3}
which has the value @code{expr2} if @code{expr1} is true, and @code{expr3}
if it is false.

See `arithmetic' for the arithmetical operators @xref{Arithmetic}.
You can test to see if a variable is defined by looking at the value
of @code{$?var} (@pxref{Define}).