The code is taken from 
    Introduction to Perl 
    or, Learn Perl in Two Hours 
    
    MU Campus Computing Short Course 
    Campus Computing, University of Missouri - Columbia 
    Document update: 24 October 1995 

Demonstration:

    () ? Howdy
    (Howdy) ? 2+5
    (7) ? sqrt(2)
    (1.4142135623730951) ? $x
    ([undefined]) ? $x = sqrt(2)
    (1.4142135623730951) ? $x + 5
    (6.4142135623730949) ? 1/0
    Illegal division by constant zero in
    file (eval) at line 2, next 2 tokens "0;"
    ([undefined]) ? system 'date'
    Fri Oct  6 20:38:01 CDT 1995
    (0) ? $x = `date`
    (Fri Oct  6 20:39:12 CDT 1995
    ) ? chop $x;
    (
    ) ? $x
    (Fri Oct  6 20:39:12 CDT 1995) ? foreach (1..10) {print sqrt()," "}
    1 1.4142135623730951 1.7320508075688772 2 2.2360679774997898
    2.4494897427831779 2.6457513110645907 2.8284271247461903 3
    3.1622776601683795 ([undefined]) ? 
    ([undefined]) ? @st=stat("lp.pl")
    (13) ? @st
    (13) ?  @st
    [0]:2
    [1]:0
    [2]:33206
    [3]:1
    [4]:0
    [5]:0
    [6]:2
    [7]:572
    [8]:876844800
    [9]:870319828
    [10]:873333799
    [11]:
    [12]:
    (13) ? exit

The last part that shows the array content is what I added. Please note the space before the @.

Please refer to the original file for explanations. Location: http://www.phlab.missouri.edu/perl/perlcourse.html