Get-FileHash

Get-FileHash
    [-Path] <String[]>
    [[-Algorithm] <String>]
    [<CommonParameters>]

Get-FileHash
    [-LiteralPath] <String[]>
    [[-Algorithm] <String>]
    [<CommonParameters>]

Get-FileHash
    [-InputStream] <Stream>
    [[-Algorithm] <String>]
    [<CommonParameters>]

The Get-FileHash cmdlet computes the hash value for a file by using a specified hash algorithm. A hash value is a unique value that corresponds to the content of the file. Rather than identifying the contents of a file by its file name, extension, or other designation, a hash assigns a unique value to the contents of a file. File names and extensions can be changed without altering the content of the file, and without changing the hash value. Similarly, the file's content can be changed without changing the name or extension. However, changing even a single character in the contents of a file changes the hash value of the file.

The purpose of hash values is to provide a cryptographically-secure way to verify that the contents of a file have not been changed. While some hash algorithms, including MD5 and SHA1, are no longer considered secure against attack, the goal of a secure hash algorithm is to render it impossible to change the contents of a file -- either by accident, or by malicious or unauthorized attempt -- and maintain the same hash value. You can also use hash values to determine if two different files have exactly the same content. If the hash values of two files are identical, the contents of the files are also identical.

By default, the Get-FileHash cmdlet uses the SHA256 algorithm, although any hash algorithm that is supported by the target operating system can be used.

This example uses the Get-FileHash cmdlet to compute the hash value for the /etc/apt/sources.list file. The hash algorithm used is the default, SHA256. The output is piped to the Format-List cmdlet to format the output as a list.

Get-FileHash /etc/apt/sources.list | Format-List

Algorithm : SHA256
Hash      : 3CBCFDDEC145E3382D592266BE193E5BE53443138EE6AB6CA09FF20DF609E268
Path      : /etc/apt/sources.list

This example uses the Get-FileHash cmdlet and the SHA384 algorithm to compute the hash value for an ISO file that an administrator has downloaded from the internet. The output is piped to the Format-List cmdlet to format the output as a list.

Get-FileHash C:\Users\user1\Downloads\Contoso8_1_ENT.iso -Algorithm SHA384 | Format-List

Algorithm : SHA384
Hash      : 20AB1C2EE19FC96A7C66E33917D191A24E3CE9DAC99DB7C786ACCE31E559144FEAFC695C58E508E2EBBC9D3C96F21FA3
Path      : C:\Users\user1\Downloads\Contoso8_1_ENT.iso

For this example, we are using System.Net.WebClient to download a package from the PowerShell release page. The release page also documents the SHA256 hash of each package file. We can compare the published hash value with the one we calculate with Get-FileHash.

$wc = [System.Net.WebClient]::new()

$baseurl = 'https://github.com/PowerShell/PowerShell/releases/download/v6.2.4/'
$pkgname = 'powershell_6.2.4-1.debian.9_amd64.deb'
$pkgurl = $baseurl + $pkgname

$publishedHash = '8E28E54D601F0751922DE24632C1E716B4684876255CF82304A9B19E89A9CCAC'
$FileHash = Get-FileHash -InputStream ($wc.OpenRead($pkgurl))
$FileHash.Hash -eq $publishedHash

True

PowerShell does not provide a cmdlet to compute the hash of a string. However, you can write a string to a stream and use the InputStream parameter of Get-FileHash to get the hash value.

$stringAsStream = [System.IO.MemoryStream]::new()
$writer = [System.IO.StreamWriter]::new($stringAsStream)
$writer.Write("Hello world")
$writer.Flush()
$stringAsStream.Position = 0
Get-FileHash -InputStream $stringAsStream | Select-Object Hash

Hash
----
64EC88CA00B268E5BA1A35678A1B5316D212F4F366B2477232534A8AECA37F3C

This cmdlet supports the common parameters: -Debug, -ErrorAction, -ErrorVariable, -InformationAction, -InformationVariable, -OutBuffer, -OutVariable, -PipelineVariable, -ProgressAction, -Verbose, -WarningAction, and -WarningVariable. For more information, see about_CommonParameters.

You can pipe a string containing a path to a file to this cmdlet.

This cmdlet returns an object representing the path to the specified file, the value of the computed hash, and the algorithm used to compute the hash.