php man page for strtr

STRTR(3)								 1								  STRTR(3)

strtr - Translate characters or replace substrings

SYNOPSIS
       string strtr (string  $str, string  $from, string  $to)

DESCRIPTION
       string strtr (string  $str, array  $replace_pairs)

	If  given  three  arguments, this function returns a copy of $str where all occurrences of each (single-byte) character in $from have been
       translated to the corresponding character in $to, i.e., every occurrence of $from[$n] has been replaced with $to[$n], where $n is  a  valid
       offset in both arguments.

	If $from and $to have different lengths, the extra characters in the longer of the two are ignored. The length of $str will be the same as
       the return value's.

	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       occurrences  of	the  array keys have been replaced by the corresponding values.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; additionally, 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.

PARAMETERS
	      o $str
		- The string being translated.

	      o $from
		- The string being translated to $to.

	      o $to
		- The string replacing $from.

	      o $replace_pairs
		- The $replace_pairs parameter may be used instead of $to and $from, in which case it's an array in the form array('from' => 'to',
		...).

RETURN VALUES
	Returns the translated string.

	If $replace_pairs contains a key which is an empty string ( ""), FALSE will be returned. If the $str is not a scalar then it is not  type-
       casted into a string, instead a warning is raised and NULL is returned.

EXAMPLES
       Example #1

	      strtr(3) example

	      <?php
	      //In this form, strtr() does byte-by-byte translation
	      //Therefore, we are assuming a single-byte encoding here:
	      $addr = strtr($addr, "aao", "aao");
	      ?>

	The  next example shows the behavior of strtr(3) when called with only two arguments. Note the preference of the replacements ( "h" is not
       picked because there are longer matches) and how replaced text was not searched again.

       Example #2

	      strtr(3) example with two arguments

	      <?php
	      $trans = array("h" => "-", "hello" => "hi", "hi" => "hello");
	      echo strtr("hi all, I said hello", $trans);
	      ?>

	      The above example will output:

	      hello all, I said hi

	The two modes of behavior are substantially different. With three arguments, strtr(3) will replace bytes; with two, it may replace  longer
       substrings.

       Example #3

	      strtr(3) behavior comparison

	      <?php
	      echo strtr("baab", "ab", "01"),"
";

	      $trans = array("ab" => "01");
	      echo strtr("baab", $trans);
	      ?>

	      The above example will output:

	      1001
	      ba01

SEE ALSO
       str_replace(3), preg_replace(3).

PHP Documentation Group 														  STRTR(3)