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unless statements

by root (Monk)
on Nov 05, 1999 at 04:10 UTC ( [id://947]=perltutorial: print w/replies, xml ) Need Help??

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

Replies are listed 'Best First'.
Re: unless statements
by htoug (Deacon) on Feb 08, 2005 at 11:09 UTC
    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 $divisor isn't equal to 0 - 'so long' indicates a repetition IMHO).
      Hello , well i think unless is a loop and things like : if ($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
what is benefit of unless ?
by Anonymous Monk on Feb 05, 2005 at 11:34 UTC
    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
      $ 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
        is this the equivalent code for " unless(condition)" ? if !(condition) { ... ... } else { ... ... } reply soon, barun parichha
      A reply falls below the community's threshold of quality. You may see it by logging in.

      It is not similar statement.

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


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