There are so much good points shown by other monks, but I have an other tip for you:

instead of

my $pi=3.141592654;

you could use

use constant PI => 3.141592654;

(in case you don't want to change PI in your program ;) )

Update: And you could use 
print << 'END', "-" x76, "\n";
Welcome to Will's Plane Geometry Calculator.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The first argument should be tri, cir, rec, or sqr.

The second argument should be area, peri, or hypo.

If you give hypo as the second argument, the next two
arguments should be the known sides of the traingle.

The peri arg will also find circumference if cir is
given for the figure. Specify the diameter to find this.

Pi is approximated at 3.141592654 (simply change my pi
if a different approximation is needed).

To find area of a circle specify the radius.

I think you can figure out the rest.
END

[download]


That is much clearer to read for me.

In reply to Re: Can't grab $ARGV[n] by Crian
in thread Can't grab $ARGV[n] by OxYgEn

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.