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batch-filedos

variable in FOR /F

I am new to write batch file I have a simple.txt and its content:

aaa 1
bbb 2
ccc 3
bbb 4
aaaa 5
aaccdd 7

and run the batch file:

@echo off
FOR /F "tokens=2 delims= " %%a in ('FindStr "aa" ^"simple.txt^"') DO (
    SET TEMP_VAR=%%a
    echo %TEMP_VAR%
)

The result is 

7
7
7

But what I expect is 

1
5
7

Why does this happen? What I am thinking it is C-like or Java-like for loop. Is it really different from them?

Solution

  • Classic problem for a person learning batch :-)

    The entire FOR loop, including the contents of the parentheses, is parsed prior to the loop executing. Normal %TEMP_VAR% expansion takes place as part of the parsing, so the value you see is the value that existed before the loop is executed.

    The solution is simple: Add setlocal enableDelayedExpansion at the top, and use !TEMP_VAR! instead.

    @echo off
setlocal enableDelayedExpansion
FOR /F "tokens=2 delims= " %%a in ('FindStr "aa" ^"simple.txt^"') DO (
    SET TEMP_VAR=%%a
    echo !TEMP_VAR!
)

    The HELP documentation provides a description of the problem. Type HELP SET or SET /? from the command line. The description of normal vs. delayed expansion is about 2/3 down from the top.