php replace first occurrence of string from 0th position [duplicate]

Answer 1

try this

preg_replace('/^[a-zA-Z]\s/', 'ReplacementWord ', $string)

what it does is select anything from start till first white space and replace it with replcementWord . notice a space after replcementWord. this is because we added \s in search string

Answer 2

preg_replace('/nothing/', 'something', $str, 1);