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Use of logical operators AND OR when comparing conditionals


( $foo && $bar ) == $baz

does not do what you think it does; it first evaluates the && operation, getting the value of $foo if $foo is true and otherwise getting the value of $bar, then compares that to $baz. You need to explicitly spell it out as $foo == $baz && $bar == $baz to test both.

If you have many values (preferably in an array, not a bunch of separate variables), grep can be useful:

if ( 2 == grep $_ == $baz, $foo, $bar )
{

List::MoreUtils provides a convenient all method, too:

use List::MoreUtils 'all';
if ( all { $_ == $baz } $foo, $bar ) {

and/or and &&/|| are not string or numeric operators; the alphabetic ones function exactly the same as the equivalent symbolic ones. The only difference is that they have different precedence; &&/|| have a higher precedence, such that they are useful within an expression; and/or have a lower precedence, such that they are useful for flow control between what are essentially different expressions. Some examples:

my $x = $y || 'default_value';

equivalent to:

my $x = ( $y || 'default_value' );

vs.

my @a = get_lines() or die "expected
some lines!";

equivalent to:

( my @a = get_lines() ) or die
"expected some lines!";

Categories : Perl

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