You want to replace a substring with a different string. For example, you want to obscure all but the last four digits of a credit card number before printing it.
Use substr_replace(), as in Example 1-15.
Replacing a substring with substr_replace( )
Without the $length argument, substr_replace( ) replaces everything from $start to the end of the string. If $length is specified, only that many characters are replaced:
print substr_replace('My pet is a blue dog.','fish.',12); print substr_replace('My pet is a blue dog.','green',12,4); $credit_card = '4111 1111 1111 1111'; print substr_replace($credit_card,'xxxx ',0,strlen($credit_card)-4); My pet is a fish. My pet is a green dog. xxxx 1111
If $start is negative, the new substring is placed at $start characters counting from the end of $old_string, not from the beginning:
print substr_replace('My pet is a blue dog.','fish.',-9); print substr_replace('My pet is a blue dog.','green',-9,4); My pet is a fish. My pet is a green dog.
If $start and $length are 0, the new substring is inserted at the start of $old_string:
print substr_replace('My pet is a blue dog.','Title: ',0,0); Title: My pet is a blue dog.
The function substr_replace( ) is useful when you've got text that's too big to display all at once, and you want to display some of the text with a link to the rest. Example 1-16 displays the first 25 characters of a message with an ellipsis after it as a link to a page that displays more text.
Displaying long text with an ellipsis
The more-text.php page referenced in Example 1-16 can use the message ID passed in the query string to retrieve the full message and display it.
1.3.4. See Also
Documentation on substr_replace( ) at http://www.php.net/substr-replace.