Another similarity between perl and shell (common to C as well), is that the second expression will not be evaluated at all if the first expression "answers the question". This matters when the second expression has side effects. Some trivial examples: 
sub f0 { return 0 }
sub f1 { return 1 }

if (( my $x = f1() ) && ( my $y = f1() ))
#  true, and both variables are set to 1


if (( my $x = f0() ) && ( my $y = f1() ))
#  false, $x is set to 0, $y is undef


if (( my $x = f0() ) || ( my $y = f1() ))
#  true, $x is set to 0, $y is set to 1


if (( my $x = f1() ) || ( my $y = f1() ))
#  true, $x is set to 1, $y is undef

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As in shell usage, this can be used to good effect, to perform (or skip) an action based on the outcome of previous action. (It can also be a trap for the unwary.)

In reply to Re: AND OR by graff
in thread AND OR by hasimir44

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