用宏变量解析多个&符号 [英] Resolving multiple ampersands with macro variables

问题描述

此代码适用于在本地运行的 SAS EG(隐藏敏感信息):

This code works in SAS EG run on local (hidden sensitive information):

*---- two values: DEV (ALIASDEV) and PROD (ALIASPROD);
%let my_environment = ALIASDEV;
%let ALIASPROD= (hidden_tns_prod);
%let ALIASDEV= (hidden_tns_dev);

libname mylib oracle user=username password='my_password' path="&&my_environment";

但是这段代码没有(使用 rsubmit;)

But this code doesn't (with rsubmit;)

rsubmit;
*---- two values: DEV (ALIASDEV) and PROD (ALIASPROD);
%let my_environment = ALIASDEV;
%let ALIASPROD= (hidden_tns_prod);
%let ALIASDEV= (hidden_tns_dev);

libname mylib oracle user=username password='my_password' path="&&my_environment";
endrsubmit;

这是错误信息:

错误:ORACLE 连接错误:ORA-12154:TNS:无法解析指定的连接标识符.错误:LIBNAME 语句中的错误.

ERROR: ORACLE connection error: ORA-12154: TNS:could not resolve the connect identifier specified. ERROR: Error in the LIBNAME statement.

我想要做的是拥有一个宏 (my_environment)，我可以在我的 dev 和 prod 数据库之间无缝切换.

What I am trying to do is having a macro (my_environment) that I can switch to work seamlessly between my dev and prod databases.

谢谢

推荐答案

我不知道为什么它在本地工作，但是&符号需要三分之一才能正确解析.每当您将一个宏变量的值存储在另一个宏变量中时，都必须使用三个与号来检索它.

I don't know why it worked on the local, but the ampersands require a third to resolve properly. Any time you store the value of a macro variable in another macro variable, you must use three ampersands to retrieve it.

基本用例:

• 两个&符号允许您将包含其他宏变量的宏变量解析为名称的部分.IE，如果你有 &val_sept 和 &val_oct，你可以使用 &&val_&mon 来检索它，假设 %let mon=sept.
• 三个 & 符号允许您检索包含为另一个宏变量的 值 的宏变量.因此，如果您有 &sept 和 &oct，那么您将使用 &&&mon. 来检索 &sept 来自变量 %let mon=sept.

• Two ampersands allows you to resolve macro variables that contain other macro variables as part of the name. IE, if you have &val_sept and &val_oct, you can use &&val_&mon to retrieve it assuming %let mon=sept.
• Three ampersands allow you to retrieve a macro variable that is contained as a value of another macro variable. So if you have &sept and &oct, then you would use &&&mon. to retrieve &sept from a variable %let mon=sept.

这是因为多个&符号如何解析；SAS 多次通过，直到全部解决.

That's because of how multiple ampersands resolve; SAS makes multiple passes through until all are resolved.

在每一关中:

1. 每对 & 符号解析为 1 个 & 符号，并被搁置一旁.
2. 如果剩下一个 & 符号，它将与后面的文本一起解析为宏变量，并替换为存储在其中的值.

所以:

%let x=a;
%let a=b;
%let b=c;

%put &&x;

1: &&x -> (&&)(x) -> (&)(x) -> &x2: &x -> a

1: &&x -> (&&)(x) -> (&)(x) -> &x 2: &x -> a

%put &&&x;

1: &&&x -> (&&)(&x) -> (&)(a) -> &a2:&a -> b

1: &&&x -> (&&)(&x) -> (&)(a) -> &a 2: &a -> b

%put &&&&x;

1: &&&&x -> (&&)(&&) (x) -> (&)(&)(x) -> &&x2:&&x -> (&&)(x) -> (&)(x) ->&x2: &x -> a

1: &&&&x -> (&&)(&&) (x) -> (&)(&)(x) -> &&x 2: &&x -> (&&)(x) -> (&)(x) -> &x 2: &x -> a

%put &&&&&x;

1: &&&&&x -> (&&)(&&)(&x) -> (&)(&)(a) -> &&a2:&&a -> (&&)(a) -> (&a)3:&a -> b

1: &&&&&x -> (&&)(&&)(&x) -> (&)(&)(a) -> &&a 2: &&a -> (&&)(a) -> (&a) 3: &a -> b

%put &&&&&&x;

1: &&&&&&x -> (&&)(&&)(&&) (x) -> (&)(&)(&)(x) -> &&&x2:&&&a -> (&&)(&x) -> (&a)3:&a -> b

1: &&&&&&x -> (&&)(&&)(&&) (x) -> (&)(&)(&)(x) -> &&&x 2: &&&a -> (&&)(&x) -> (&a) 3: &a -> b

四个 & 号对我来说是最有趣的，因为添加一个实际上会让你后​​退一步，有效地.

Four ampersands is the most interesting to me, since adding one actually takes you back a step, effectively.

有关详细信息，请参阅我在 sas MACRO && 上的回答.

See my answer on sas MACRO ampersand for more detail.

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