This method uses only a single special (??{...}) expression within the RE, but unfortunately it requires that you know the named variable name of the string being passed to it. (See Update1) 

my $string = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
my ($random) = $string =~ m/(??{'.'x rand length $string })(.)/s;
print $random, "\n";

[download]

------------
UPDATE1: And here it is without the dependancy on knowing the name of the scalar holding the string (Thanks perlre). 

my $string = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
my( $random ) = $string =~ m/^(??{ '.' x rand length $_ })(.)/s;
print "$random\n";

[download]

I knew there had to be a way. ;)

------------
UPDATE2: And here it is with a quantifier instead of a huge string of '.' metacharacters. The code is longer, but it's more friendly to real long target strings. 

my $string = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
my ($random) = $string =~ m/^
                            (??{'.{' . int(rand length $_) . '}' })
                            (.)
                           /sx;
print "$random\n";

[download]

Enjoy!


Dave

In reply to Re: Pick a random string char with a regex by davido
in thread Pick a random string char with a regex by bsb

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.