I guess you user would seperate their addresses with a space or a comma. I would check on that.

Something like: 

#!/usr/bin/perl -w

use strict;

sub is_single
{
        my $email = shift;
        # remove spaces from beginning and end
        $email =~ s/^\s*|\s*$//g;
        # check for characters invalid in an emailaddress
        return $email=~/[\s,]/?0:1;
}

# prints 1
print is_single('hpotter@hotmail.com');

# prints 0
print is_single('hpotter@hotmail.com, mickymouse@disney.com');

[download]

But I guess some people around here have a far more beautiful solution.

Update strict-ing the code and making it more verbose

In reply to Re: Checking on multiple email addresses in a string by wine
in thread Checking on multiple email addresses in a string by c

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.