To find a substring in a string from right to left, you can use the regular expressions too, but using Perl rindex function is faster and easier to understand. Try to avoid using regular expressions for simple string operations especially when some built-in functions specially designed for this purpose are available. The regex have to manipulate memory variables, so keep them for more sophisticated and complex operations.

Before beginning with, you can skim a bit through Perl index page in order to better understand the topic discussed here.

rindex STR,SUBSTR,POSITION 
rindex STR,SUBSTR

• STR - the string you are searching
• SUBSTR - the substring whose position you want to locate or to search for
• POSITION – if specified, represents the rightmost position that can be returned, from that position the function will search from right to left looking for the substring to match

Please examine the code below to see some simple examples about how to use the Perl rindex function:

# initialize a scalar string variable
my $str = "Perl while Perl if Perl foreach";
my $substr = "Perl";
my $pos = rindex $str, $substr;
my $pos1 = rindex($str, $substr, 15); 
print "\$pos = $pos, \$pos1 = $pos1\n";
# it displays pos = 19, $pos1 = 11

If the substring is not found, rindex returns -1, otherwise it returns the last position of the occurrence of the substring.

# initialize a string scalar
my $textStr = "PDF::Create is a Perl module";
if((my $pos = rindex(lc $textStr, lc "perl")) >= 0)
{
  print "We found it!\n";
}

# initialize a string scalar
my $url = "http://www.mysite.com/perl-rindex.html";
my $pos = length($url)-1;

print "/ found at positions: ";

while(1)
{
  $pos = rindex($url, "/", $pos);
  last if($pos < 0);
  print $pos--, " ";
}

print "\n";

/ found at positions: 29 6 5