Found in /usr/lib/perl5/5.8.0/pod/perlfaq6.pod
  What's wrong with using grep or map in a void context?

    The problem is that both grep and map build a return
    list, regardless of the context.  This means you're
    making Perl go to the trouble of building a list that
    you then just throw away. If the list is large, you
    waste both time and space.  If your intent is to
    iterate over the list then use a for loop for this
    purpose.

Found in /usr/lib/perl5/5.8.0/pod/perlfaq8.pod
  What's wrong with using backticks in a void context?

    Strictly speaking, nothing.  Stylistically speaking,
    it's not a good way to write maintainable code.  Perl
    has several operators for running external commands. 
    Backticks are one; they collect the output from the
    command for use in your program.  The "system" function
    is another; it doesn't do this.

    Writing backticks in your program sends a clear message
    to the readers of your code that you wanted to collect
    the output of the command.  Why send a clear message
    that isn't true?

    Consider this line:

        `cat /etc/termcap`;

    You forgot to check $? to see whether the program even
    ran correctly. Even if you wrote

        print `cat /etc/termcap`;

    this code could and probably should be written as

        system("cat /etc/termcap") == 0
            or die "cat program failed!";

    which will get the output quickly (as it is generated,
    instead of only at the end) and also check the return
    value.

    system() also provides direct control over whether shell
    wildcard pro- cessing may take place, whereas backticks
    do not.
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