Updating a txt file of variables in powershell - powershell

Question

So my challenge today.
I have a config file (really just a txt document) that stores variables to store information passed between scripts or to be used after restarts.
I am looking for a more efficient way to read and update the file. Currently I read the file with:
Get-Content $current\Install.cfg | ForEach-Object {
Set-Variable -Name line -Value $_
$a, $b = $line.Split('=')
Set-Variable -name $a -Value $b
}
But to overwrite the contents, I recreate the file with:
ECHO OSV=$OSV >>"$ConfigLoc\tool.cfg"
ECHO OSb=$OSb >>"$ConfigLoc\tool.cfg"
ECHO cNum=$cNum >>"$ConfigLoc\tool.cfg"
ECHO cCode=$cCode >>"$ConfigLoc\tool.cfg"
ECHO Comp=$Comp >>"$ConfigLoc\tool.cfg"
Each time I have added a new saved variable, I have just hardcoded the new variable into both the original config file and the config updater.
As my next updates require an additional 30 variables to my current 15. I would like something like:
Get-Content $current\Install.cfg | ForEach-Object {
Set-Variable -Name line -Value $_
$a, $b = $line.Split('=')
ECHO $a=$$a
}
Where $$a uses the variable $a in the loop as the variable name to load the value.
Best example i can show to clarify is:
ECHO $a=$$a (in current loop)
Echo OSV=$OSV (actually appears in code as)
Not sure how to clarify this anymore, or how to achieve it with the variable title also being a variable.

Answer 1

If you want to create a file that has name=value parameters, here's an alternate suggestion. This is a snippet of a real script I use every day. You might modify it so it reads your .csv input and uses it instead of the hard coded values.
$Sites = ("RawSiteName|RoleName|DevUrl|SiteID|HttpPort|HttpsPort", `
"SiteName|Name of role|foo.com|1|80|443" `
) | ConvertFrom-CSV -Delimiter "|"
$site = $sites[0]
Write-Host "RawSiteName =$($site.RawSiteName)"
You might be able to use something similar to $text = Get-Content MyParameters.csv and pipe that to the ConvertFrom-CSV cmdlet. I realize it's not a direct answer to what you are doing but it will let you programmatically create a file to pass across scripts.

Answer 2

Thanks for the help everyone. This is the solution I am going with. Importing and exporting couldn't be simpler. If I have to manually update the XML install default I can with ease which is also amazing. I also love the fact that even if you import as $Test you can still use $original to access variables. I will be creating multiple hashtables to organize the different data I will be using going forward and just import/export it in a $config variable as the master.
$original = #{
OSV='0'
OSb='0'
cNum='00000'
cCode='0000'
Client='Unknown'
Comp='Unknown'
}
$original | Export-Clixml $Home\Desktop\sample.cfg
$Test = Import-Clixml $Home\Desktop\sample.cfg
Write $Test
Write $original.Client

Answer 3

In essence, you're looking for variable indirection: accessing a variable indirectly, via its name stored in another variable.
In PowerShell, Get-Variable allows you to do that, as demonstrated in the following:
# Sample variables.
$foo='fooVal'
$bar='barVal'
# List of variables to append to the config file -
# the *names* of the variables above.
$varsToAdd =
'foo',
'bar'
# Loop over the variable names and use string expansion to create <name>=<value> lines.
# Note how Get-Variable is used to retrieve each variable's value via its *name*.
$(foreach ($varName in $varsToAdd) {
"$varName=$(Get-Variable $varName -ValueOnly)"
}) >> "$ConfigLoc/tool.cfg"
With the above, the following lines are appended to the output *.cfg file:
foo=fooVal
bar=barVal
Note that you can read such a file more easily with the ConvertFrom-StringData, which outputs a hashtable with the name-value pairs from the file:
$htSettings = Get-Content -Raw "$ConfigLoc/tool.cfg" | ConvertFrom-StringData
Accessing $htSettings.foo would then return fooVal, for instance.
With a hashtable as the settings container, updating the config file becomes easier, as you can simply recreate the file with all settings and their current values:
$htSettings.GetEnumerator() |
ForEach-Object { "$($_.Key)=$($_.Value)" } > "$ConfigLoc/tool.cfg"
Note: PowerShell by default doesn't enumerate the entries of a hashtable in the pipeline, which is why .GetEnumerator() is needed.
Generally, though, this kind of manual serialization is fraught, as others have pointed out, and there are more robust - though typically less friendly - alternatives.
With your string- and line-based serialization approach, there are two things to watch out for:
All values are saved as a strings, so you have to manually reconvert to the desired data type, if necessary - and even possible, given that not all objects provide meaningful string representations.
Generally, the most robust serialization format is Export-CliXml, but note that it is not a friendly format - be careful with manual edits.
ConvertFrom-StringData will fail with duplicate names in the config file, which means you have to manually ensure that you create no duplicate entries when you append to the file - if you use the above approach of recreating the file from a hashtable every time, however, you're safe.