PHP str_replace Function

Another key tool to have in your programming toolbox is the ability to quickly replace parts of a PHP string with new values. The str_replace function is similar to a word processor's "Replace All" command that lets you specify a word and what to replace it with, then replaces every occurrence of that word in the document.

str_replace Parameters

str_replace has three parameters that are required for the function to work properly. str_replace(search, replace, originalString).

1. search - This is what you want to search your string for. This can be a string or an array.
2. replace - All matches for search will be replaced with this value. This can be a string or an array.
3. originalString - This is what search and replace will be operating on. The str_replace function will return a modified version of originalString when it completes.

str_replace Simple Example

Imagine we are working at a school district and need to create a webpage for the students' parents. The webpage has an introduction string that we need to customize depending on if the student is male or female. With str_replace this is mighty easy.

//string that needs to be customized
$rawstring = "Welcome Birmingham parents. Your replaceme is a pleasure to have!";

//male string
$malestr = str_replace("replaceme", "son", $rawstring);

//female string
$femalestr = str_replace("replaceme", "daughter", $rawstring);

echo "Son: ". $malestr . "<br />";
echo "Daughter: ". $femalestr;

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With these two gender customized strings created we could then provide a more engaging experience for the student's parents when they logged into the school website with their kid's credentials.

str_replace Arrays: Multiple Replaces in One

In the last example we only needed to replace one word replaceme in our string, but what if we wanted to replace many words? We could just use the function multiple times to get the job done, or we could create an array of placeholders and a second array of replace values to get it all done in one function call.

The key thing to understand with this technique is that you are creating two arrays that will be used to swap values. The first item in placeholders will be replaced by the first item in the replace values, the second item of placeholders replaced with the second in replace values and so on and so forth.

Let's extend our simple example to be a complete form letter addressed to a student's parents.

//string that needs to be customized
$rawstring = "Welcome Birmingham parent! <br />
	Your offspring is a pleasure to have! 
	We believe pronoun is learning a lot.<br />
	The faculty simple adores pronoun2 and you can often hear 
	them say \"Attah sex!\"<br />";

//placeholders array
$placeholders = array('offspring', 'pronoun', 'pronoun2', 'sex');
//male replace values array
$malevals = array('son', 'he', 'him', 'boy');
//female replace values array
$femalevals = array('daughter', 'she', 'her', 'girl');

//male string
$malestr = str_replace($placeholders, $malevals, $rawstring);

//female string
$femalestr = str_replace($placeholders, $femalevals, $rawstring);

echo "Son: ". $malestr . "<br />";
echo "Daughter: ". $femalestr;

Display:

Notice: there is a bug in this code. The placeholder pronoun2 did not get replaced in the way we intended (our strings have he2 and she2 instead of him and her). This is because all instances of pronoun were replaced first and the pronoun in pronoun2 was replaced at this time with he or she, making he2 or she2. When it was pronoun2's turn to be replaced, there were no matches to be found, so our string has no him or her.

To fix this bug you could simply make sure that pronoun2 comes first in the placeholders array and by updating the values of the male and female replace values to reflect this.

// ...snip
//placeholders array
$placeholders = array('offspring', 'pronoun2', 'pronoun',  'sex');
//male replace values array
$malevals = array('son', 'him', 'he',  'boy');
//female replace values array
$femalevals = array('daughter', 'her', 'she',  'girl');
//snip...

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