Constructing an array from a text file in Powershell

If the command is not a Powershell cmdlet like Kolob Canyon's answer then you would need to parse the text. Here's an inelegant example using -match and regex to find the lines with Location and Usable space [KB] and find the word characters after the colon.

((Get-Content C:\Example.txt -Raw) -split 'Medium identifier') | ForEach-Object {
    [void]($_ -match 'Location\s+:\s(.*?(\w+).*)\r')
    $Location = @($Matches.values | Where-Object {$_ -notmatch '\W'})[0]
    [void]($_ -match 'Usable\sspace\s\[KB\]\s+:\s(.*?(\w+).*)\r')
    $UsableSpace = @($Matches.values | Where-Object {$_ -notmatch '\W'})[0]
    if ($Location -or $UsableSpace){
        [PSCustomObject]@{
            Location = $Location
            UsableSpace = $UsableSpace
        }
    }
}

As this is extremely fragile and inelegant, it's much better to interact with an object where ever possible.

Assuming the data is as regular as it looks, you could use multiple assignment to extract the data from the array as in:

$data = 1, 2, "ignore me", 3, 10, 22, "ignore", 30
$first, $second, $null, $third, $data = $data

where the first, second and fourth array elements go into the variables, "ignore me" gets discarded in $null and the remaining data goes back into data. In your case, this would look like:

# Read the file into an array
$data = Get-Content data.txt

# Utility to fix up the data row
function FixUp ($s)
{
    ($s -split ' : ')[1].Trim()
}

# Loop until all of the data is processed
while ($data)
{
    # Extract the current record using multiple assignment
    # $null is used to eat the blank lines
    $identifier,$null,$label,$location,$owner,$status,
        $used,$total,$space,$writes,$overwrites,
        $errors, $initialized, $lastwrite, $lastaccess,
        $lastOverwrite, $protected, $writeprotected,
        $null, $null, $data = $data

    # Convert it into a custom object 
    [PSCustomObject] [ordered] @{
        Identifier   = fixup $identifier
        Label        = fixup $label
        location     = fixup $location
        Owner        = fixup $owner
        Status       = fixup $status
        Used         = fixup $used
        Total        = fixup $total
        Space        = fixup $space
        Write        = fixup $writes
        OverWrites   = fixup $overwrites
        Errors       = fixup $errors
        Initialized  = fixup $initialized
        LastWrite    = [datetime] (fixup $lastwrite)
        LastAccess   = [datetime] (fixup $lastaccess)
        LastOverWrite = [datetime] (fixup $lastOverwrite)
        Protected    = fixup $protected
        WriteProtected = fixup $writeprotected
    }
}

Once you have the data extracted, you can format it any way you want

That looks a very regular pattern, so I'd say there are three typical approaches to this.

First: your own bucket-fill-trigger-empty parser, load lines in until you reach the next trigger ("Medium identifier"), then empty out the bucket to the pipeline and start a new one.

Something like:

$bucket = @{}

foreach ($line in Get-Content -LiteralPath C:\path\data.txt)
{
    # if full, empty bucket to pipeline
    if ($line -match '^Medium identifier')
    {
        [PSCustomObject]$bucket
        $bucket = @{}
    }

    # add line to bucket (unless it's blank)
    if (-not [string]::IsNullOrWhiteSpace($line))
    {
        $left, $right = $line.Split(':', 2)
        $bucket[$left.Trim()] = $right.Trim()
    }
}

# empty last item to pipeline
[PSCustomObject]$bucket

Adjust to taste for identifying numbers, dates, etc.

Second: a multiline regex: I tried, but can't. It would look something like:

# Not working, but for example:
$r = @'
Medium identifier    : (?<MediumIdentifier>.*)
\s*
Write-protected      : (?<WriteProtected>.*)
Blocks used  [KB]    : (?<BlockesUsed>.*)
Medium label         : (?<MediumLabel>.*)
Last write           : (?<LastWrite>.*)
Medium Owner         : (?<MediumOwner>.*)
Usable space [KB]    : (?<UsableSpaceKB>.*)
Number of overwrites : (?<NumberOfOverwrites>.*)
Last overwrite       : (?<LastOverwrite>.*)
Medium identifier    : (?<MediumIdentifier>.*)
Blocks total [KB]    : (?<BlocksTotalKB>.*)
Number of errors     : (?<NumberOfErrors>.*)
Medium initialized   : (?<MediumInitialized>.*)
Status               : (?<Status>.*)
Location             : (?<Location>.*)
Protected            : (?<Protected>.*)
Number of writes     : (?<NumberOfWrites>.*)
Last access          : (?<LastAccess>.*)
\s*
'@

[regex]::Matches((get-content C:\work\a.txt -Raw), $r, 
    [System.Text.RegularExpressions.RegexOptions]::IgnoreCase + 
    [System.Text.RegularExpressions.RegexOptions]::Singleline
    )

Third: ConvertFrom-String - http://www.lazywinadmin.com/2014/09/powershell-convertfrom-string-and.html or https://blogs.technet.microsoft.com/ashleymcglone/2016/09/14/use-the-new-powershell-cmdlet-convertfrom-string-to-parse-klist-kerberos-ticket-output/ then after you made the template

Get-Content data.txt | ConvertFrom-String -TemplateFile .\template.txt

The easiest way is to use the command itself and select certain properties. If the command is a powershell cmdlet, it should return an Object.

$output = Some-HPCommand | select 'Medium label', 'Location' 

Then you can access specific properties:

$output.'Medium label'
$output.Location

If you can provide the exact command, I can write this more accurately.

The biggest issue when people are learning powershell is they treat output like a String... Everything in PowerShell is object-oriented, and once you begin to think in terms of Objects, it becomes much easier to process data; in other words, always try to handle output as objects or arrays of objects. It will make your life a hell of a lot easier.

If each section is in the same format, i.e. the Usable space section is always 5 lines down from the location then you can use the Select-String in combination with the context parameter. Something like this:

Select-String .\your_file.txt -Pattern '(?<=Location\s*:\s).*' -Context 0, 5 | % {
    New-Object psobject -Property @{
        Location = (($_.Matches[0] -replace '\[|\]', '') -split ':')[0]
        UsableSpace = ($_.Context.PostContext[4] -replace '^\D+(\d+)$', '$1' )
    }
}