char * strcasestr(const char *, const char *) __ATTR_PURE__
The strcasestr() function finds the first occurrence of the
substring s2 in the string
s1. This is like strstr(), except that it ignores case of alphabetic symbols in searching for
the substring. (Glibc, GNU extension.)
The strcasestr() function returns a pointer to the beginning of
the substring, or NULL if the substring is not
found. If s2 points to a string of zero length, the
function returns s1.