if, unless

Synopsis:
if (<condition>) <then>
if (<condition>) { <then> } [{ <else> }]
if (<condition>) { <else> } elsif (<condition>) { <then> } else { <then> }

Description:
if is the general purpose control statement for testing the truth/false value of a given condition. If the condition is true, it performs some action; if false, some alternate action. The condition does not necessarily need to be a numeric comparison. It may be a function whose return value is evaluated for truth or falsity, or compared against some other value (which might also be a function return value). Expressions are generally of the following forms:
( exp ) tests for existence of exp (usually a variable)
( !exp ) tests for non-existence of exp
( exp1 == exp2 ) tests whether exp1 equals exp2
( exp1 != exp2 ) tests whether exp1 does not equal exp2
( exp1 && exp2 ) tests for existence of exp1 and exp2
( exp1 || exp2 ) tests for existence of exp1 or exp2 or both
( exp1 ^^ exp2 ) tests for existence of exp1 or exp2, not both
( exp1 < exp2 ) tests whether exp1 is less than exp2
( exp1 > exp2 ) tests whether exp1 is more than exp2
( exp1 <= exp2 ) tests whether exp1 is less than or equal to exp2
( exp1 >= exp2 ) tests whether exp1 is more than or equal to exp2

The "else" portion of an if statement is not required. Additionally, if the "then" portion is only a single statement, the curly braces are not required either. The expression (exp) is evaluated as though it were within a ${ } construct, such that
if ( blah ) ...
would expand "blah" to $blah, then test the value of $blah. Variables can also be placed inside the expression parser, such that
if ( [$blah] ) ...
is equivalent to the previous statement (though it isn't as efficient). Both forms may be combined in the same expression. Numbers are treated as constants, so in order to expand numeric expandos, such as $0, you must use the expression parser, as above. Strings must also be passed through the expression parser (otherwise they are interpreted as variables), and are compared case-insensitively. As in C, assignment operators may be used inside if statements. This is generally not recommended, if only because it can make the code rather confusing, but there are times when it can prove to be useful. The following:
if ( foo = 3 > bar ) ...
would first set the value of $foo to 3, and then compare it with $bar. Note that the @ operator is not needed (and in fact is not even allowed). Gratuitous use of parenthesis is recommended with this notation. Finally, as with other TekNap control statements, the curly braces may be placed anywhere.

Examples:
The following two statements are functionally equivalent:
if ( foo == bar ) echo foo and bar are the same
if ( foo == bar ) {
..echo foo and bar are the same
}

These are also equivalent:
if ( !foo ) ...
unless ( foo ) ...

Braces are required for a multi-line then portion:
if ( foo == bar ) {
..echo foo and bar are the same
..echo that's so cool!
}

Like other control statements, ifs may be embedded:
if ( foo ) {
..if ( bar ) {
....echo foo and bar are the same echo that's so cool!
..}
}

Function return values can be evaluated too:
if ( rmatch(foobar *blah* *bar) ) {
..echo it matched
}

Aliases:
unless is the exact opposite of if. It is essentially the same applying the negation operator (!) to the entire if condition.

Other Notes:
The "then" and "else" portions aren't required to contain anything. Use of the negation operator and unless obsolete this practice, however.

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