c:\test>p1
[0] Perl> $a = 'abcdeee';;
[0] Perl> $a =~ /(..)/ and print $1;;
ab
[0] Perl> $a =~ /(.)\1/ and print $1;;
e
[0] Perl> $a =~ /((.)\1)/ and print $2;;
[0] Perl> $a =~ /((.)\1)/ and print $1;;
[0] Perl> $a =~ /(.)(\1+)/ and print "$1$2";;
eee
[0] Perl> $a = 'abcdeeef';;
[0] Perl> $a =~ /(.)(\1+)/ and print "$1$2";;
eee
[0] Perl> $a = 'abbb;eeef';;
[0] Perl> $a =~ /(.)(\1+)/ and print "$1$2";;
bbb