China DOS Union

Ask a question, there is a function I have always not known how to implement.

For example:

First set the following two variables:

set a=1

set b1=10

Then execute echo %b%a%% to get %b1%

In fact, what I want to get is the value assigned to b1, that is, 10

Ask everyone, can it be achieved?

[ Last edited by HAT on 2008-12-23 at 10:10 ]

```
@echo off
set a=1&set b1=10
call,echo %%b%a%%%
pause>nul
```

It turns out it can be achieved. Thanks to the expert upstairs. But there are still some doubts. What does "call" mean in the line "call,echo %%b%a%%%"? I can't do it directly by echoing "%%b%a%%%", but it works... I know that "call" is used to call other batch files or labels, and the comma behind it is confusing.

Originally posted by hongewuyan at 2008-6-23 17:33:
It really works.
Thanks to the expert above.

But there are still some doubts.

call,echo %%b%a%%%

Can you explain this line? What does call mean?
I can't do it directly with echo %%b%a%%%, but it works when adding call. ...

Here, call actually reorganizes and expands the command line. First, expand %a% inside %%b%a%%% so that %a% becomes the value 1 of a, and then use cal to expand %b1%.

It can also be implemented using variable delay. The method is as follows:
@echo off set /a a=1,b1=10 Setlocal EnableDelayedExpansion echo:!b%a%! ... pause

The usage of call here is actually a quick way of variable delay. Variable delay is generally used in the loop body of for.

In call,%%b%a%%%, the comma here is actually a separator, the same as a space. There are many separators available. For example, in the above example, echo:!b%a%! ，Of course, not all commands can be used in this way, depending on the situation...

C:\>echo+cn-dos.net
cn-dos.net

C:\>echo/cn-dos.net
cn-dos.net

C:\>echo

My understanding is that if there are still variables within variables, you need to use variable delay call delay or setlocal to enable delay. I wonder if this understanding is correct...

Thanks everyone for your help, I really understand this time...

Originally posted by bat-zw at 2008-6-23 17:15:
@echo off set a=1&set b1=10 call,echo %%b%a%%% pause>nul

Why does adding a space on both sides of the & connecting the two set statements, that is: set a=1 & set b1=10, result in "ECHO is off"?

Originally posted by mysuntjy at 2008-12-23 07:13:

Why does adding a space on both sides of & connecting two set statements, that is: set a=1 & set b1=10, the running result is: ECHO is off.

????

After adding the space, the value of variable a is 1 plus a space, not the original single 1.

In the statement `call,echo %%b%a%%`, the extra `%` signs are related to how batch processing in Windows handles variable expansion. In a batch file, when you want to literally output a `%` character, you need to use `%%` because the single `%` is used for variable substitution. Let's break it down:

The part `%%b%a%%` - the first `%%` is to output a single `%` before the variable `b`, then `%a%` is the variable `a` with the surrounding `%` signs, and the last `%%` is to output a single `%` after. If you just wrote `call,echo %b%a%%`, there would be issues with how the batch parser interprets the variable expansion and the literal `%` characters. So the extra `%` signs are there to correctly handle the literal `%` output and proper variable expansion in the batch processing context.

Explanation of Escape Character %
http://www.cn-dos.net/forum/viewthread.php?tid=19077#pid112069

Detailed Explanation of Variable Delay
http://www.cn-dos.net/forum/viewthread.php?tid=28273

When to Use Variable Delay
http://www.cn-dos.net/forum/viewthread.php?tid=20733

A Problem of Nested Variables
http://www.cn-dos.net/forum/viewthread.php?tid=41143

Haha, suddenly I see the light.
A good post shouldn't sink, top it to let more people see!