Batch: Comparing arrays

Question

I'm trying to compare two arrays in batch script, but I'm afraid I'm doing it wrong. The code below retrieves the first 12 bytes from a file and tries to compare it with a given format.

Could you help help me with the TODO part?

PS: I'm not sure if I'm using the array variables correctly..

@echo off

SETlocal enabledelayedexpansion
SET read_byte_cmd=powershell -command Get-Content -encoding Byte -TotalCount 12 "'DB.accdb'" 

SET ACCESS_BYTES[0]=0
SET ACCESS_BYTES[1]=1
SET ACCESS_BYTES[2]=0
SET ACCESS_BYTES[3]=83
SET ACCESS_BYTES[4]=116
SET ACCESS_BYTES[5]=97
SET ACCESS_BYTES[6]=110 
SET ACCESS_BYTES[7]=100
SET ACCESS_BYTES[8]=97
SET ACCESS_BYTES[9]=114
SET ACCESS_BYTES[10]=100
SET ACCESS_BYTES[11]=32

echo list array --------------------
SET ACCESS_BYTES[
echo\

echo list file bytes --------------
set i=0
for /f "tokens=1 delims==" %%i in ('%read_byte_cmd%') do (
    set /A i+=1
    echo %read_byte_array[!i!]%=%%i
    )
echo\

echo list values only --------------
for /f "tokens=2 delims==" %%i in ('SET ACCESS_BYTES[') do echo %%i
echo\

echo comparison --------------------
:: TODO compare ACCESS_BYTES[i] with read_byte_array[i], if equal success..

You define your array starting with 0, but in your for loop you start to index with 1 (enter the for with i=0, adding one, then echo...[!i!]. Intention or logical quirk? — Stephan
– Stephan, Commented May 30, 2016 at 10:26
Do all bytes need to be the same? If so, couldn't you just compare a single variable with all bytes (using ; as delimiter if needed) to see if they are equal. — Dennis van Gils
– Dennis van Gils, Commented May 30, 2016 at 12:13
@Stephan No quirk, only the result of multiple tries to fix the code... — lbrunolx
– lbrunolx, Commented May 30, 2016 at 15:23
@Dennis All bytes have to be the same, but besides that, there is no limitation regarding how it should be done. Array vs array was just my 1st approach.. — lbrunolx
– lbrunolx, Commented May 30, 2016 at 15:23

Dennis van Gils · Accepted Answer · 2016-06-01 15:48:51Z

1

I think you're looking for something like this:

@echo off

SETlocal enabledelayedexpansion
SET read_byte_cmd=powershell -command Get-Content -encoding Byte -TotalCount 12 "'DB.accdb'" 

SET "ACCESS_BYTES=[0,1,0,83,116,97,110,100,97,114,100,32]"
set "READ_BYTES=["
for /f "tokens=1 delims==" %%i in ('%read_byte_cmd%') do (
    set "READ_BYTES=!READ_BYTES!%%i,"
)
set "READ_BYTES=%READ_BYTES:~0,-1%]"
echo %ACCESS_BYTES%
echo %READ_BYTES%
echo.
if "%READ_BYTES%"=="%ACCESS_BYTES%" echo same
if not "%READ_BYTES%"=="%ACCESS_BYTES%" echo not the same
pause

This doesn't use the arrays, but just compares two variables.

edited Jun 1, 2016 at 15:48

answered May 30, 2016 at 12:24

Dennis van Gils

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6 Comments

lbrunolx Over a year ago

Dennis, thanks a bunch. But I'm still dwelling with it. Your code stops at element [1], printing the message "byte 1, value 1 is not equal to", when it should cycle through all elements (because they are equal). It seems like the code is not iterating through the array ACCESS_BYTES (always stays at 0)...

Dennis van Gils Over a year ago

@lbrunolx error on my part, could you tell me if it gives a better message now? I also made the loop start at 0, not at 1. Did it print succes before the error message?

lbrunolx Over a year ago

Dennis, I'm afraid it is still stopping at [1]. I get: read_byte_array[0]=0 correct read_byte_array[1]=1 byte 1, value 1 is not equal to 0 not all bytes were the same

Dennis van Gils Over a year ago

@lbrunolx seems like I messed up my delayed expansion, will fix that in a minute

Dennis van Gils Over a year ago

@lbrunolx yeah, the final problem was that the variable i contained a number, which caused it to sometimes be interpreted (when using an escaped %% aproach) as %1, which starts looking at parameters of the batch file. However, this approach doesn't have that problem

|

Community · Accepted Answer · 2020-06-20 09:12:55Z

Your batch script is invoking PowerShell, which is a much more powerful language for data processing. Why not also do the comparison in PowerShell? The Compare-Object cmdlet (alias diff) can quickly compare two arrays, and the array syntax is PowerShell is much simpler than CMD.

Compare-AccessBytes.ps1

$bytes = Get-Content -Encoding Byte -TotalCount 12 'DB.accdb'
$target = @(0,1,0,83,116,97,110,100,97,114,100,32)

if ((diff $bytes $target).length -eq 0) {
  "Matching"
} else {
  "Different"
}

To invoke from batch

PowerShell.exe -ex bypass -f Compare-AccessBytes.ps1

If you need to capture this into a batch variable, use for /F syntax to capture the output of the script.

for /f %%a in ('PowerShell.exe -ex bypass -f Compare-AccessBytes.ps1') do if "%%a"=="Matching" (echo Yep, it matches.) else (echo Sorry, nope)

Finally, if a batch file is the only audience for your .ps1, it is even easier to have PowerShell communicate directly with CMD in its native dialect: Exit codes.

Compare-AccessBytes2.ps1

$bytes = Get-Content -Encoding Byte -TotalCount 12 'DB.accdb'
$target = @(0,1,0,83,116,97,110,100,97,114,100,32)
if ((diff $bytes $target).length -eq 0) { exit 12345 }

In your batch, run the command and check ERRORLEVEL.

PowerShell.exe -ex bypass -f Compare-AccessBytes.ps1
if %ERRORLEVEL% EQU 12345 (
   echo "Declare a holiday, the bytes match!"
) else (
   echo "So sad, no match today."
)

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