$all = get_defined_functions()['internal'];
$str_functions = array_filter($all, fn($f) => str_starts_with($f, 'str'));
print_r($str_functions);
/*
run:
Array
(
[4] => strlen
[5] => strcmp
[6] => strncmp
[7] => strcasecmp
[8] => strncasecmp
[57] => strtotime
[64] => strftime
[386] => stream_wrapper_register
[387] => stream_register_wrapper
[388] => stream_wrapper_unregister
[389] => stream_wrapper_restore
[524] => strptime
[568] => strspn
[569] => strcspn
[571] => strcoll
[580] => strtok
[581] => strtoupper
[582] => strtolower
[586] => stristr
[587] => strstr
[588] => strchr
[589] => strpos
[590] => stripos
[591] => strrpos
[592] => strripos
[593] => strrchr
[594] => str_contains
[595] => str_starts_with
[596] => str_ends_with
[606] => strtr
[607] => strrev
[611] => stripcslashes
[612] => stripslashes
[613] => str_replace
[614] => str_ireplace
[617] => strip_tags
[620] => str_getcsv
[621] => str_repeat
[623] => strnatcmp
[625] => strnatcasecmp
[627] => str_pad
[629] => str_rot13
[630] => str_shuffle
[631] => str_word_count
[632] => str_split
[633] => strpbrk
[811] => stream_select
[812] => stream_context_create
[813] => stream_context_set_params
[814] => stream_context_get_params
[815] => stream_context_set_option
[816] => stream_context_get_options
[817] => stream_context_get_default
[818] => stream_context_set_default
[819] => stream_filter_prepend
[820] => stream_filter_append
[821] => stream_filter_remove
[822] => stream_socket_client
[823] => stream_socket_server
[824] => stream_socket_accept
[825] => stream_socket_get_name
[826] => stream_socket_recvfrom
[827] => stream_socket_sendto
[828] => stream_socket_enable_crypto
[829] => stream_socket_shutdown
[830] => stream_socket_pair
[831] => stream_copy_to_stream
[832] => stream_get_contents
[833] => stream_supports_lock
[834] => stream_set_write_buffer
[836] => stream_set_read_buffer
[837] => stream_set_blocking
[839] => stream_get_meta_data
[841] => stream_get_line
[842] => stream_resolve_include_path
[843] => stream_get_wrappers
[844] => stream_get_transports
[845] => stream_is_local
[846] => stream_isatty
[847] => stream_set_chunk_size
[848] => stream_set_timeout
[857] => strval
[881] => stream_bucket_make_writeable
[882] => stream_bucket_prepend
[883] => stream_bucket_append
[884] => stream_bucket_new
[885] => stream_get_filters
[886] => stream_filter_register
)
*/
