Powershell - Implementing looping to access elements in a hash algorithm

Question

The function I wrote here accepts three mandatory parameters: an input file, a list containing at least one hash algorithm(s), and an output file that saves the hash values of that input file. This function attempts to accept three needed parameters: input file, list of at least one hash algorithms, and output file that saves the hashed values of that input file. I am trying to complete the function by writing the code needed to efficiently and effectively implement this function in the specified block. I am attempting to implement some form of looping to access the elements in $hashAlgorithm.

function Return-FileHash { 
param ( 
[Parameter(Position=0,Mandatory=$true,ValueFromPipeline=$true)] 
[ValidateSet("SHA1","SHA256","SHA384","SHA512","MD5")] 
[STRING[]] 
# the array list that contains one or more hash algorithm input for Get-FileHash cmdlet 
$hashAlgorithm, 
[Parameter(Position=1, Mandatory=$true,ValueFromPipeline=$true)] 
# the document or executable input/InputStream for Get-FileHash cmdlet 
$filepath, 
[Parameter(Position=2,Mandatory=$true,ValueFromPipeline=$true)] 
# the output file that contains the hash values of $filepath 
$hashOutput 
) 
#============================ begin ==================== 
# Here, I am trying to use a loop expression to implement this
for( $i = 0; $i -lt $hashAlgorithm.Length; $i++)
{
Get -FileHash $hashAlgorithm -SHA1 | $hashOutput
}

# === end ================= 
Return-FileHash

I get this:

At line:19 char:38
+ Get -FileHash $hashAlgorithm -SHA1 | $hashOutput
+                                      ~~~~~~~~~~~
Expressions are only allowed as the first element of a pipeline.
At line:1 char:26
+ function Return-FileHash {
+                          ~
Missing closing '}' in statement block or type definition.
    + CategoryInfo          : ParserError: (:) [], ParentContainsErrorRecordException
    + FullyQualifiedErrorId : ExpressionsMustBeFirstInPipeline

Mathias R. Jessen · Accepted Answer · 2020-04-28 16:34:16Z

1

To access the individual elements of $hashAlgorithm in the for loop, index into it with the current value of $i:

for ( $i = 0; $i -lt $hashAlgorithm.Length; $i++) {
    Get-FileHash $filepath -Algorithm $hashAlgorithm[$i] | ...
}

Alternatively use a foreach() loop:

foreach($algo in $hashAlgorithm.Length) {
    Get-FileHash $filepath -Algorithm $algo | ...
}

To output to a file at path $hashOutput, either use the file redirection operators:

# `>` means "overwrite"
Get-FileHash $filepath -Algorithm $hashAlgorithm[$i] > $hashOutput
# `>>` means "append"
Get-FileHash $filepath -Algorithm $hashAlgorithm[$i] >> $hashOutput

Or pass $hashOutput as an argument to a command that writes the output to disk:

Get-FileHash $filepath -Algorithm $hashAlgorithm[$i] | Add-Content -Path $hashOutput

edited Apr 28, 2020 at 16:34

answered Apr 28, 2020 at 16:28

Mathias R. Jessen

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