while ( <DATA> ) {
    chomp;
    print "$_: ", 
          /^a.*b$/ && !/.ab./
              ? "yes"
              : "no",
          "\n";
}

__DATA__
a000000000b
a0a0000b00b
a0000ab000b
ab00000000b
a000ab

##</code><code>##

a000000000b: yes
a0a0000b00b: yes
a0000ab000b: no
ab00000000b: yes
a000ab: yes