substr() function in php

//substr($str, startIndex, length)

//The interception direction is from left to right.

//If length is not written, it will be intercepted to the last one by default.

//length is the exact number, negative is the index (length from the bottom)

//Note that startIndex starts from 0.

//The length includes the characters on startIndex, length is 2, which is startIndex, startIndex+1 two

echo substr('abcdef', -4);//start is -4, which means starting from the second to last one until the end. So return cdef

echo '
';

echo substr('abcdef', 0);//start is 0, which means starting from the first one, abcdef

echo '
';

echo substr('abcdef' , 1, 3);//Three characters starting from the second, bcd

echo '
';

echo substr('abcdef', -3, 2);//Starting from the third from the bottom Two characters, de

echo '
';

echo substr('abcdef', -3, -2);//Starting from the third to last, to the second to last, and excluding the second to last ,d