PHP ships with dozens of built-in string functions. The most-used ones let you measure, transform, and slice strings without writing any loops yourself.
strlen() returns the number of bytes in a string.strtolower() / strtoupper() change case.substr() extracts a portion of a string.str_replace() replaces all occurrences of a search value.These four functions alone cover the majority of everyday string work.
<?php
$str = 'Hello, World!';
echo strlen($str); // 13
echo strtolower($str); // hello, world!
echo strtoupper($str); // HELLO, WORLD!
echo substr($str, 7, 5); // World
echo str_replace('World', 'PHP', $str); // Hello, PHP!
// substr with negative offset counts from the end
echo substr($str, -6); // orld! (last 6 chars... wait: World! = 6)
Tip: substr() accepts a negative offset to count from the end of the string, and a negative length to omit characters from the end — very handy for trimming file extensions.