The mysql php extension has been deprecated after php5.4. The following functions are affected and should be replaced with the mysqli extension. Note differences in parameter order:

mysql_affected_rows -> mysqli_affected_rows($link)
mysql_close -> mysqli_close($link)
mysql_data_seek -> mysqli_data_seek( $result, $offset)
mysql_errno -> mysqli_errno( $link)
mysql_error -> mysqli_error( $link)
mysql_fetch_array -> mysqli_fetch_array( $result, $type)
mysql_fetch_assoc -> mysqli_fetch_assoc( $result)
mysql_fetch_lengths -> mysqli_fetch_lengths( $result )
mysql_fetch_object -> mysqli_fetch_object( $result, $class, $params)
mysql_fetch_row -> mysqli_fetch_row( $result)
mysql_field_seek -> mysqli_field_seek( $result, $number)
mysql_free_result -> mysqli_free_result(result)
mysql_get_client_info -> mysqli_get_client_info( $link)
mysql_get_host_info -> mysqli_get_host_info( $link)
mysql_get_proto_info -> mysqli_get_proto_info( $link)
mysql_get_server_info -> mysqli_get_server_info( $link)
mysql_info -> mysqli_info( $link)
mysql_insert_id -> mysqli_insert_id( $link)
mysql_num_rows ->  mysqli_num_rows( $result)
mysql_ping -> mysqli_ping( $link)
mysql_query -> mysqli_query( $link, $query)
mysql_real_escape_string -> mysqli_real_escape_string( $link)
mysql_select_db - > mysqli_select_db( $link, $database)
mysql_set_charset -> mysqli_set_charset( $link, $charset)
mysql_stat -> mysqli_stat( $link)
mysql_thread_id -> mysqli_thread_id( $link)

Code substitutions using VIM

:%s/mysql_/mysqli_/g
:%s/mysqli_query(/mysqli_query(\$db,/g
:%s/mysqli_error()/mysqli_error(\$db)/g
:%s/mysqli_errno()/mysqli_errno(\$db)/g

:%s/mysqli_real_escape_string(/mysqli_real_escape_string(\$db,/g
:wn

Further changes:

mysql_select_db vs mysqli_select_db needs parameters swapped

add global $db; to functions
replace eregi('') with preg_match('//i')
replace ereg('') with preg_match('//')
replace ereg_replace('') with preg_replace('//')
replace eregi_replace('') with eregi_replace('//i')

replace split with explode