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
[download]

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.)

---

---

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:

  <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>

• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or How to display code and escape characters are good places to start.