CODEWITHSUNDEEP
windowspowershellbatch-filefindstr
xnstad
xnstad

Reputation: 3

Findstr always fails to find hash string in text file

I'm trying to replace a certain .jar file if the MD5 hash of the file changes. I've written a small PowerShell script to do the hashing of the file and the .ps1 script is run through a batch file.

After PowerShell prints the hash into 1.txt I want the batch script to check the text file for the correct hash and if the hash is different it will overwrite the file with the old version. The replacing of the file is not yet implemented but will be once the findstr issue is resolved.

@echo off
setlocal EnableDelayedExpansion

:a
powershell.exe -ExecutionPolicy ByPass -file powershellmd5.ps1

findstr /c:"ff b1 b9 2d b1 03 db 59 3f 9e ca 51 f0 14 67 62 ca a8 d7 7d" "1.txt"
echo !errorlevel!
timeout /t 10 /NOBREAK
goto a

Here is the content of 1.txt when the hashing is complete:

SHA1 hash of file license.jar:
ff b1 b9 2d b1 03 db 59 3f 9e ca 51 f0 14 67 62 ca a8 d7 7d
CertUtil: -hashfile command completed successfully.

The errorlevel is always 1, even though the string is identical to the one in the text file. Maybe I am using the arguments wrong?

I'm using Out-File in powershellmd5.ps1 to write the result:

certutil -hashfile license.txt | Out-File 1.txt

Upvotes: 0

Views: 1215

Answers (3)

Aacini
Aacini

Reputation: 67206

Accordingly to the comments posted in this question I think there are some misconceptions on this topic, that I try to clear.

All command-line based applications included with Windows are primarily designed to work with cmd.exe and Batch files. As a matter of fact, one of the features of PowerShell is that it "can use command-line applications in the same way as cmd.exe do". There is not a single command-line based application designed to work with PowerShell, but not with cmd.exe/Batch file.

In my humble opinion the use of PowerShell in this topic is not just unnecessary, but it is also the cause of the original problem. The pure Batch-file code below should run as originally intended, with no problems:

@echo off
setlocal EnableDelayedExpansion

:a
certutil -hashfile license.jar > "1.txt"

findstr /c:"ff b1 b9 2d b1 03 db 59 3f 9e ca 51 f0 14 67 62 ca a8 d7 7d" "1.txt"
echo !errorlevel!
timeout /t 10 /NOBREAK
goto a

As an additional point, the time required to run this pure Batch file is much lesser than the required to run the PowerShell-based one.

Upvotes: 1

Ansgar Wiechers
Ansgar Wiechers

Reputation: 200193

Apparently you're using Out-File for creating 1.txt. The cmdlet uses Unicode (little endian UTF-16) as the default encoding, which findstr doesn't support. The command processes the file as ASCII¹ text and thus can't find a match.

There are two ways of approaching this problem:

  • Write 1.txt using ASCII encoding, either by calling Out-File with the -Encoding parameter:

    certutil -hashfile license.txt | Out-File 1.txt -Encoding Ascii

    or by calling Set-Content (which defaults to ASCII encoding):

    certutil -hashfile license.txt | Set-Content 1.txt

  • Use the find command (which supports Unicode) instead of findstr:

    find "ff b1 b9 2d b1 03 db 59 3f 9e ca 51 f0 14 67 62 ca a8 d7 7d" 1.txt

¹ Yes, I know, it's actually an ANSI encoding, but the parameter argument is named Ascii, so let's stick with that name for now to avoid confusion.

Upvotes: 3

xnstad
xnstad

Reputation: 3

Instead of using findstr I used FC (filecompare). I let powershell create 1.txt and then I copied the content over to 2.txt and saved it as unicode.

The white spaces in the file generated by powershell seems to not be regular spaces and use of the /W to suppress white spaces and /U for parsing the files as Unicode is necessary to make it work.

The code is now as following:

@echo off
setlocal EnableDelayedExpansion

:a

powershell.exe -ExecutionPolicy ByPass -file powershellmd5.ps1
timeout /t 3 /NOBREAK

fc /U /W /lb3 1.txt 2.txt

IF NOT ERRORLEVEL 1 ( 
    echo Indentical.
) else (
    echo Different.
)
pause


del /q 1.txt

timeout /t 10 /NOBREAK

goto a

The script now successfully compares both files, returns error code 0 and prints Identical"

Upvotes: 0

Related Questions