swap two words in a string php

Question

Suppose there's a string "foo boo foo boo" I want to replace all fooes with boo and booes with foo. Expected output is "boo foo boo foo". What I get is "foo foo foo foo". How to get expected output rather than current one?

    $a = "foo boo foo boo";
    echo "$a\n";
    $b = str_replace(array("foo", "boo"), array("boo", "foo"), $a);
    echo "$b\n";
    //expected: "boo foo boo foo"
   //outputs "foo foo foo foo"

Answer 1

Use strtr

From the manual:

If given two arguments, the second should be an array in the form array('from' => 'to', ...). The return value is a string where all the occurrences of the array keys have been replaced by the corresponding values. The longest keys will be tried first. Once a substring has been replaced, its new value will not be searched again.

In this case, the keys and the values may have any length, provided that there is no empty key; additionaly, the length of the return value may differ from that of str. However, this function will be the most efficient when all the keys have the same size.

$a = "foo boo foo boo";
echo "$a\n";
$b = strtr($a, array("foo"=>"boo", "boo"=>"foo"));
echo "$b\n"; 

Outputs

foo boo foo boo
boo foo boo foo

In Action

Answer 2

Perhaps using a temporary value like coo.

sample code here,

$a = "foo boo foo boo";
echo "$a\n";
$b = str_replace("foo","coo",$a);
$b = str_replace("boo","foo",$b);
$b = str_replace("coo","boo",$b);
echo "$b\n";

Answer 3

First foo to zoo. Then boo to foo and last zoo to boo

$search = array('foo', 'boo', 'zoo');
$replace = array('zoo', 'foo', 'boo');
echo str_replace($search, $replace, $string);