As perldoc -f sort will tell you, the sort verb in Perl takes a subroutine name or an in-line code block as its argument. That piece of code is handed two variables named $a and $b corresponding to the two items now being compared, and it must return a value that is less than, equal to, or greater than zero. Perl provides a special operator, <=>, specifically to assist with this. Also cmp ... which compares strings. (Do not get tripped-up by this peculiarity of Perl!)
The || operator is also useful because it is a “short-circuit logical-OR.” If the expression on the left side is nonzero (“true”), the right side won't be evaluated. Perfect for chaining comparisons together to sort by more than one field.
For anything but very simple cases, I prefer to define a separate sort-comparison subroutine, because an in-line code block can easily devolve into “chicken scratches.” The code, however you choose to write it, should be extremely obvious, able to be tested in isolation, and also very easily changed. It will be executed tens of thousands of times.
-
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.
|