Get-FileHash
SYNOPSIS
Computes the hash value for a file by using a specified hash algorithm.
SYNTAX
Path (Default)
Get-FileHash [-Path] <String[]> [[-Algorithm] <String>] [<CommonParameters>]
LiteralPath
Get-FileHash [-LiteralPath] <String[]> [[-Algorithm] <String>] [<CommonParameters>]
StreamParameterSet
Get-FileHash [-InputStream] <Stream> [[-Algorithm] <String>] [<CommonParameters>]
DESCRIPTION
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.
EXAMPLES
Example 1: Compute the hash value for a file
Get-FileHash /etc/apt/sources.list | Format-List
Algorithm : SHA256
Hash : 3CBCFDDEC145E3382D592266BE193E5BE53443138EE6AB6CA09FF20DF609E268
Path : /etc/apt/sources.list
Example 2: Compute the hash value for an ISO file
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
Example 3: Compute the hash value of a stream
$wc = [System.Net.WebClient]::new()
$pkgurl = 'https://github.com/PowerShell/PowerShell/releases/download/v6.2.4/powershell_6.2.4-1.debian.9_amd64.deb'
$publishedHash = '8E28E54D601F0751922DE24632C1E716B4684876255CF82304A9B19E89A9CCAC'
$FileHash = Get-FileHash -InputStream ($wc.OpenRead($pkgurl))
$FileHash.Hash -eq $publishedHash
True
Example 4: Compute the hash of a string
$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
PARAMETERS
-Algorithm
Specifies the cryptographic hash function to use for computing the hash value of the contents of the specified file or stream. A cryptographic hash function has the property that it is infeasible to find two different files with the same hash value. Hash functions are commonly used with digital signatures and for data integrity. The acceptable values for this parameter are:
- SHA1
- SHA256
- SHA384
- SHA512
- MD5
If no value is specified, or if the parameter is omitted, the default value is SHA256.
For security reasons, MD5 and SHA1, which are no longer considered secure, should only be used for simple change validation, and should not be used to generate hash values for files that require protection from attack or tampering.
Type: System.String
Parameter Sets: (All)
Aliases:
Accepted values: SHA1, SHA256, SHA384, SHA512, MD5
Required: False
Position: 1
Default value: None
Accept pipeline input: False
Accept wildcard characters: False
-InputStream
Specifies the input stream.
Type: System.IO.Stream
Parameter Sets: StreamParameterSet
Aliases:
Required: True
Position: 0
Default value: None
Accept pipeline input: False
Accept wildcard characters: False
-LiteralPath
Specifies the path to a file. Unlike the Path parameter, the value of the LiteralPath parameter is used exactly as it is typed. No characters are interpreted as wildcard characters. If the path includes escape characters, enclose the path in single quotation marks. Single quotation marks instruct PowerShell not to interpret characters as escape sequences.
Type: System.String[]
Parameter Sets: LiteralPath
Aliases: PSPath, LP
Required: True
Position: 0
Default value: None
Accept pipeline input: True (ByPropertyName)
Accept wildcard characters: False
-Path
Specifies the path to one or more files as an array. Wildcard characters are permitted.
Type: System.String[]
Parameter Sets: Path
Aliases:
Required: True
Position: 0
Default value: None
Accept pipeline input: True (ByPropertyName, ByValue)
Accept wildcard characters: False
CommonParameters
This cmdlet supports the common parameters: -Debug, -ErrorAction, -ErrorVariable, -InformationAction, -InformationVariable, -OutVariable, -OutBuffer, -PipelineVariable, -Verbose, -WarningAction, and -WarningVariable. For more information, see about_CommonParameters.
INPUTS
System.String
You can pipe a string to the `Get-FileHash` cmdlet that contains a path to one or more files.
OUTPUTS
Microsoft.Powershell.Utility.FileHash
`Get-FileHash` returns an object that represents the path to the specified file, the value of the computed hash, and the algorithm used to compute the hash.