unless statements

[root]

Unless statements allow you to say unless something is true do this. For example:

$value=20;
unless($divisor==0){      #so long as the $divisor isn't equal to 0
  $value=$value/$divisor; #go ahead and divide $value by $divisor
} else {
  $divisor=1;             #otherwise set $divisor to 1
}

If you've got that I suggest you take a look at while loops

[htoug]

It is a matter of taste (and style), but I only use unless without the else-clause. If you have the else, then you could just as well use a normal if and get better readability - it's more like waht everyone is used to.

But in a standalone if (!(some_complicated_expression)) the use of unless lets you remove one pair of parenthesis and lets the poor smuck reading the code have one less thing to worry about.

I would rewrite your example as

$value=20;
if ($divisor!=0){      #so long as the $divisor isn't equal to 0
  $value=$value/$divisor; #go ahead and divide $value by $divisor
} else {
  $divisor=1;             #otherwise set $divisor to 1
}

Now the statement says the same as the comment (in your code it should have been #unless the $divisor isn't equal to 0 - 'so long' indicates a repetition IMHO).

[Anonymous Monk]

Hello , well i think unless is a loop and things like : if ($divisor!=0){ doesn't work rather than using unless if will procedes the action for one time but unless will keep procedes the same things unless the statment goes wrong that's what i think

[Anonymous Monk]

I think unless statements are similar to if statements.But if-else stmt gives us more flexibility then unless.So is there any specific use of this . please reply soon. regards, barun parichha

[holli]

$ cat input
foo



bar
$ perl -ne 'print unless /^$/../^$/' input
foo
bar
$ perl -ne 'print if not /^$/../^$/' input
foo
bar
$ perl -ne 'print if ! /^$/../^$/' input
foo

bar

The unless statement is equivalent to if not, but is different from if ! due to the associativity and precedence rules covered in perlop. A benefit of this behavior allows the reduction of runs of blank lines to a single blank line.

taken from here

[Anonymous Monk]

You can use "else" with "unless".

"unless" means "if not", so it reverses the meaning of an "if" comparison.

See perlsyn for details.

Please read Where should I post X? and How (Not) To Ask A Question.

[Anonymous Monk]

is this the equivalent code for " unless(condition)" ? if !(condition) { ... ... } else { ... ... } reply soon, barun parichha

[prasadbabu]

It is not similar statement.

$a = 10;
print "if stmt true" if ($a == 10);
print "unless" unless ($a == 10);