CODEWITHSUNDEEP
batch-file
georgiana_e
georgiana_e

Reputation: 1869

variables expansion inside for in batch

I am new to batch and I don't understand when to use late variable expansion or normal expansion. Below I have a test script in which I have tested the variables expansion. I have noticed that inside for, only delayed expansion works. However I would like to use normal expansion inside the for.

@echo off

setlocal
set var=0
echo late var=!var!
echo var=%var%

for /F "delims= " %%A in (temp.txt) do (
        echo Analyzing %%A
        set line=%%A
        echo line=%line%
        echo late line=!line!
)
endlocal

Output:

late var=0
var=0
Analyzing bb
line=
late line=bb
Analyzing aa
line=
late line=aa
Analyzing cc
line=
late line=cc

Why do I have in for only delayed expansion and how can I use normal expansion inside the for? Thanks.

Upvotes: 0

Views: 138

Answers (2)

foxidrive
foxidrive

Reputation: 41224

This can work depending on the text being parsed, as poison characters can affect it.

@echo off
set var=0
echo late var=%var%
echo var=%var%

for /F "delims= " %%A in (temp.txt) do call :next "%%A"
goto :EOF
:next
        echo Analyzing %~1
        set line=%~1
        echo line=%line%
        echo late line=%line%

Upvotes: 3

MC ND
MC ND

Reputation: 70923

When a line or a block of code (the code enclosed in parenthesis in your for, if, ... ) is reached, the parser removes all variable reads, replacing them with the value inside the variable before the line/block starts to execute. So, if the value of a variable is changed inside a line/block, this changed value is not visible inside that same line/block since all access to the variable content has been replaced with its value.

So, if the value of the variable is changed inside a line/block AND the changed value of the variable needs to be read/accessed inside the same line/block, delayed expansion is needed.

for and if commands are places where this is usually more evident, but constructs as 

set "data=test"
....
set "data=other test" & echo %data%

shows the same problem. When the parser handles the last line, %data% is replaced with its value, and then the line is executed. So the final line executed is

set "data=other test" & echo test

Upvotes: 3

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