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); $$ = $1; };variable:            |    base_variable_with_function_calls { $$ = $1; };base_variable_with_function_calls:        base_variable                { $$ = $1; }    ;reference_variable:    |    compound_variable            { zend_do_begin_variable_parse(TSRMLS_C); fetch_simple_variable(&$$, &$1, 1 TSRMLS_CC); };compound_variable:        T_VARIABLE            { $$ = $1; }    |    ‘$‘ ‘{‘ expr ‘}‘    { $$ = $3; };

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_OPLINE    zval *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_WIN32    fflush(stderr);#endif    return str_len;}