<?php

	$str = "aaaaaaaaaa";
	$carater="-";
	$apartir=3;
	$ate=7;
	$ambos="ambos";
	$entre="entre";
	$compr=strlen($str);
	
	if ($apartir==3){
	 $nome=substr($str, $compr-$apartir, $compr);
	 $right = str_pad($nome, $compr, $carater, STR_PAD_RIGHT);
	}
	
	if ($ate==7){
	  $nome=substr($str, $compr-$apartir, $compr);
	  $left = str_pad($nome, $compr, $carater, STR_PAD_LEFT);
	}
	
	if($ambos=="ambos"){
		$nome=substr($str, $ate, $compr);
		$both = str_pad($nome, $compr, $carater, STR_PAD_BOTH);
	}
	
	    echo $right;
	    echo "\n";
	    echo $left;
	    echo "\n";
	    echo $both;
	    echo "\n";
	
	$quant=2;
	
	$parts = str_split($str, $quant);
	$inicio = $fim = $parts[0]; 
	
	$aux=substr($str,$quant*2,$compr);
	
	$compl=str_replace("a",$carater,$aux);
	
	$meio=$inicio.$compl.$fim;
	echo $meio;