unticked_statement:
|    T_ECHO echo_expr_list ';'
;
echo_expr_list:echo_expr_list ',' expr { zend_do_echo(&$3 TSRMLS_CC); }|    expr                    { zend_do_echo(&$1 TSRMLS_CC); }
;
expr:r_variable                    { $$ = $1; }|    expr_without_variable        { $$ = $1; }
;
r_variable:variable { zend_do_end_variable_parse(&$1, BP_VAR_R, 0 TSRMLS_CC); $$ = $1; }
;
variable:base_variable_with_function_calls
;
base_variable_with_function_calls:base_variable                { $$ = $1; }
;
base_variable:reference_variable { $$ = $1; $$.EA = ZEND_PARSED_VARIABLE; }
;
reference_variable:|    compound_variable            { zend_do_begin_variable_parse(TSRMLS_C); fetch_simple_variable(&$$, &$1, 1 TSRMLS_CC); }
;compound_variable:T_VARIABLE            { $$ = $1; }|    '$' '{' expr '}'    { $$ = $3; }
;|    compound_variable            { zend_do_begin_variable_parse(TSRMLS_C); fetch_simple_variable(&$$, &$1, 1 TSRMLS_CC); }
;
compound_variable:T_VARIABLE            { $$ = $1; }

void zend_do_echo(const znode *arg TSRMLS_DC) /* {{{ */
{zend_op *opline = get_next_op(CG(active_op_array) TSRMLS_CC);opline->opcode = ZEND_ECHO;SET_NODE(opline->op1, arg);SET_UNUSED(opline->op2);
}

static int ZEND_FASTCALL  ZEND_ECHO_SPEC_CV_HANDLER(ZEND_OPCODE_HANDLER_ARGS)
{USE_OPLINEzval *z;SAVE_OPLINE();z = _get_zval_ptr_cv_BP_VAR_R(EX_CVs(), opline->op1.var TSRMLS_CC); //这个z已经是值了if (IS_CV == IS_TMP_VAR && Z_TYPE_P(z) == IS_OBJECT) {INIT_PZVAL(z);}zend_print_variable(z);CHECK_EXCEPTION();ZEND_VM_NEXT_OPCODE();
}

static zend_always_inline zval *_get_zval_ptr_cv_BP_VAR_R(zval ***CVs, zend_uint var TSRMLS_DC)
{zval ***ptr = &CV(var); //EG(active_op_array).vars[key]该结果是个zend_compile_variable ，其中key为znod_op的变量var,是个数字，可理解为第几个变量，最终在EG(active_sysbole_table)中取出数据，放到EX(CVs)[key]中if (UNEXPECTED(*ptr == NULL)) {return *_get_zval_cv_lookup_BP_VAR_R(ptr, var TSRMLS_CC);}return **ptr;
}static zend_never_inline zval **_get_zval_cv_lookup_BP_VAR_R(zval ***ptr, zend_uint var TSRMLS_DC)
{zend_compiled_variable *cv = &CV_DEF_OF(var);if (!EG(active_symbol_table) ||zend_hash_quick_find(EG(active_symbol_table), cv->name, cv->name_len+1, cv->hash_value, (void **)ptr)==FAILURE) {zend_error(E_NOTICE, "Undefined variable: %s", cv->name);return &EG(uninitialized_zval_ptr);}return *ptr;
}

ZEND_API int zend_print_variable(zval *var)
{return zend_print_zval(var, 0);
}ZEND_API int zend_print_zval(zval *expr, int indent) /* {{{ */
{return zend_print_zval_ex(zend_write, expr, indent);
}ZEND_API int zend_print_zval_ex(zend_write_func_t write_func, zval *expr, int indent) /* {{{ */
{zval expr_copy;int use_copy;zend_make_printable_zval(expr, &expr_copy, &use_copy);if (use_copy) {expr = &expr_copy;}if (Z_STRLEN_P(expr) == 0) { /* optimize away empty strings */if (use_copy) {zval_dtor(expr);}return 0;}write_func(Z_STRVAL_P(expr), Z_STRLEN_P(expr));if (use_copy) {zval_dtor(expr);}return Z_STRLEN_P(expr);
}int php_module_startup(sapi_module_struct *sf, zend_module_entry *additional_modules, uint num_additional_modules)
{zend_utility_functions zuf;zend_utility_values zuv;int retval = SUCCESS, module_number=0;    /* for REGISTER_INI_ENTRIES() */。。。。。。。。。。。。。。sapi_module = *sf;php_output_startup();zuf.error_function = php_error_cb;zuf.printf_function = php_printf;zuf.write_function = php_output_wrapper;zuf.fopen_function = php_fopen_wrapper_for_zend;zuf.message_handler = php_message_handler_for_zend;zuf.block_interruptions = sapi_module.block_interruptions;zuf.unblock_interruptions = sapi_module.unblock_interruptions;zuf.get_configuration_directive = php_get_configuration_directive_for_zend;zuf.ticks_function = php_run_ticks;zuf.on_timeout = php_on_timeout;zuf.stream_open_function = php_stream_open_for_zend;zuf.vspprintf_function = vspprintf;zuf.getenv_function = sapi_getenv;zuf.resolve_path_function = php_resolve_path_for_zend;zend_startup(&zuf, NULL TSRMLS_CC);

static int php_output_wrapper(const char *str, uint str_length)
{TSRMLS_FETCH();return php_output_write(str, str_length TSRMLS_CC);
}
PHPAPI int php_output_write(const char *str, size_t len TSRMLS_DC)
{if (OG(flags) & PHP_OUTPUT_DISABLED) {return 0;}if (OG(flags) & PHP_OUTPUT_ACTIVATED) {php_output_op(PHP_OUTPUT_HANDLER_WRITE, str, len TSRMLS_CC);return (int) len;}return php_output_direct(str, len);
}
static int (*php_output_direct)(const char *str, size_t str_len) = php_output_stderr;static int php_output_stderr(const char *str, size_t str_len)
{fwrite(str, 1, str_len, stderr); //可知道echo 是用fwrite输出的
/* See http://support.microsoft.com/kb/190351 */
#ifdef PHP_WIN32fflush(stderr);
#endifreturn str_len;
}