The built-in functions of PHP can dramatically improve the efficiency of your code in the area of looping. When you encounter a block of PHP code that iteratively calls a built-in function, take time to see if a more efficient way of achieving the same task is available through a different, yet related, built-in function.

For example, it's faster to prepare a large string with UIDs and call imap_fetch_overview once than it is to call imap_fetch_overview repeatedly in a loop. See the user-contributed comments for the imap_fetch_overview function in the PHP manual for more details.

Similarly, when reading large files it is far more efficient to read, say, a line at a time (using fgets) and process that, than it is to read and process a character at a time (using fgetc). There are many other similar cases throughout the PHP language, depending on exactly what your application does.