How does batch Echo parse variables in text

Question

How to batch echo output value is from another file, and the content is a variable, how to parse it?

example:

env.bat

@echo off
set a=123
set b = 456

set dev_env=%a%
set prod_env=%b%

copy_env.bat

@echo off
for /f "skip=1 eol=: tokens=2,3 delims== " %%i in (.\env.bat) do (
    setlocal enabledelayedexpansion
    set key=%%i
    set value=%%j

    echo !key!=!value! >> .\custom_variable.properties

    endlocal
)

output: this is not what I want

dev_env=%a%
prod_env=%b%

output: I want ....

dev_env=123
prod_env=456

You are basically parsing the BAT file and interpreting it like the command line processor? And implement that in Batch? Wow! I thought I do crazy stuff sometimes, but I never imagined this. — Thomas Weller
– Thomas Weller, Commented Jan 19, 2022 at 6:30
You have to run env.bat at some point in the same instance of the command prompt that copy_env.bat is running in for %a% and %b% to actually exist. Stick a call env.bat at the top of copy_env.bat and also fix your third line in env.bat so that you're setting %b% correctly. — SomethingDark
– SomethingDark, Commented Jan 19, 2022 at 6:37
Other ideas: Run the batch file to actually set the environment variables. Or use a programming language like C++, C#, Python, Java or anything that can do real programming with string replacement etc. — Thomas Weller
– Thomas Weller, Commented Jan 19, 2022 at 6:42
@SomethingDark thank you for your answer , but I've tried that It's null eg: dev_env="" — seth
– seth, Commented Jan 19, 2022 at 6:45

SomethingDark · Accepted Answer · 2022-01-19 06:50:11Z

2

You need to actually call env.bat at some point so that the variables get set. Also, because echo !key!=!value! by itself will display dev_env=%a%, etc. you need to use call for a second pass of variable expansion.

@echo off
setlocal enabledelayedexpansion

call env.bat
for /f "skip=1 eol=: tokens=2,3 delims== " %%i in (.\env.bat) do (
    set key=%%i
    set value=%%j

    call echo !key!=!value! >>.\custom_variable.properties
)

answered Jan 19, 2022 at 6:50

SomethingDark

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5 Comments

Thomas Weller Over a year ago

I am pretty sure it can be solved without calling the batch file given enough time and effort.

SomethingDark Over a year ago

@ThomasWeller - Sure, but there's no reason not to call it; as the name indicates, it's a script meant to initialize environment variables.

seth Over a year ago

awesome ! it's correct

seth Over a year ago

@SomethingDark sorry i hava a question how to determines that the character is in the text repeat?

Aacini Over a year ago

@ThomasWeller: See my answer above...

Aacini · Accepted Answer · 2022-01-19 19:19:13Z

Ok. Three points here:

First of all, the lines in the env.bat file will not be executed inside the env.bat file itself, but in a posterior execution in the copy_env.bat file, right? For this reason, the values of a and b can not be taken via an "immediate" %a% and %b% expansion, but via a "delayed" !a! and !b! one instead.
In second place, in copy_env.bat you have the setlocal enabledelayedexpansion and endlocal commands inside the for /F loop. This means that every value that is set in a for iteration will be lost when such an iteration ends. In order to preserve the values for the next for /F cycles, the setlocal-endlocal commands must be moved outside the for /F loop.
Finally, you have this command: echo !key!=!value! that just display a line like a=123, but you have not a command with the real assignment of such a value. It is necessary to add the equivalent set !key!=!value! command in order to store such values for the posterior assignments.

The final working programs are these ones:

env.bat:

@echo off
set a=123
set b = 456

set dev_env=!a!
set prod_env=!b!

copy_env.bat:

@echo off
setlocal enabledelayedexpansion
for /f "skip=1 eol=: tokens=2,3 delims== " %%i in (.\env.bat) do (
    set key=%%i
    set value=%%j

    set !key!=!value!
    echo !key!=!value! >> .\custom_variable.properties

)
endlocal

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