fwiw, rindex appears to be slightly faster: 
use Benchmark qw(timethese);

my $s = "abcdefg";

timethese( 6_000_000,
    {
        rindex => sub { my $i = rindex( $s, "cde" ) },
         index => sub { my $i =  index( $s, "cde" ) },
    }
);

[download]
Benchmark: timing 6000000 iterations of index, rindex...
index: 1 wallclock secs ( 1.14 usr + 0.00 sys = 1.14 CPU) @ 5263157.89/s (n=6000000)
rindex: 1 wallclock secs ( 1.02 usr + 0.00 sys = 1.02 CPU) @ 5882352.94/s (n=6000000)
their functional difference is that rindex starts from the end of the string, and index starts at the beginning. there is no difference in their usage.

In reply to Re: what is the difference between index and rindex by mreece
in thread what is the difference between index and rindex by jesuashok

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.