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Convert a hashtable's keys to a list of strings. Ask Question 5. I wanted to do string::Join. Browse other questions tagged arrays string powershell hashtable or ask your own question. How do I read / convert an InputStream into a String in Java? Convert bytes to a string? How do I make the first letter of a string.
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I want to take a step back and talk about. I use these all the time now. I was teaching someone about them after our user group meeting last night and I realized I had the same confusion about them at first that he had. Hashtables are really important in Powershell so it is good to have a solid understanding of them. Index.Hashtable as a collection of thingsI want you to first see a Hashtable as a collection in the traditional definition of a hashtable. This gives you a fundamental understanding of how they work when they get used for more advanced stuff later.
Skipping this understanding is often a source of confusion. What is an array?Before I jump into what a Hashtable is, I need to mention first. For the purpose of this discussion, an array is a list or collection of values or objects.
$array2 = 13I just scratched the surface on arrays but that should put them into the right context as I move onto hashtables. What is a hashtable?I am going to start with a basic technical description of what hashtables are in the general sense as used by most programming languages before I shift into the other ways Powershell makes use of them.A hashtable is a data structure much like an array, except you store each value (object) using a key. It is a basic key/value store.
First, we create an empty hashtable. $environments@('QA','DEV')$environments('QA','DEV')$environments'QA','DEV'In this example I use the same lookup hashtable from above and provide 3 different array styles to get the matches. This is a hidden gem in PowerShell that most people are not aware of. Iterating hashtablesBecause a hashtable is a collection of key/value pairs, you have to iterate over it differently than you would an array or a normal list of items.The first thing to notice is that if you pipe your hashtable, the pipe treats it like one object. $person.clearThis is one of those instances where using the function creates self documenting code and it makes the intentions of the code very clean.
All the fun stuff Ordered hashtablesBy default, hashtables are not ordered (or sorted). In the traditional context, the order does not matter when you always use a key to access values. You may find that when using it to hold properties that you may want them to stay in the order that you define them. Thankfully, there is a way to do that with the ordered keyword. $people ConvertTo-JSON Set-Content -Path $path$people = Get-Content -Path $path -Raw ConvertFrom-JSONThere are two important points about this method. First is that the JSON is written out multiline so I need to use the -Raw option to read it back into a single string. The Second is that the imported object is no longer a hashtable.
It is now a pscustomobject and that can cause issues if you don’t expect it.If you need it to be a hashtable on import, then you need to use the Export-CliXml and Import-CliXml commands. Converting JSON to HashtableIf you need to convert JSON to a hashtable, there is one way that I know of to do it with the in.Net. $content = Get-Content -Path $Path -Raw -ErrorAction Stop$scriptBlock = scriptblock::Create( $content )$scriptBlock.CheckRestrictedLanguage( $allowedCommands, $allowedVariables, $true )$hashtable = ( & $scriptBlock )It imports the contents of the file into a scriptblock, then checks to make sure it does not have any other PowerShell commands in it before it executes it.On that note, did you know that a module manifest (the psd1 file) is just a hashtable? Keys are just stringsI didn’t want to go off on this tangent earlier, but the keys are just strings. So we can put quotes around anything and make it a key. Full name'$key = 'full name'$person.$keyJust because you can do something, it does not mean that you should. That last one just looks like a bug waiting to happen and would be easily misunderstood by anyone reading your code.Technically your key does not have to be a string but they are easier to think about if you only use strings.
PSBoundParametersis an automatic variable that only exists inside the context of a function. It contains all the parameters that the function was called with.
This isn’t exactly a hashtable but close enough that you can treat it like one.That includes removing keys and splatting it to other functions. If you find yourself writing proxy functions, take a closer look at this one.See for more details.
PSBoundParameters gotchaOne important thing to remember is that this only includes the values that are passed in as parameters. If you also have parameters with default values but are not passed in by the caller, PSBoundParameters will not contain those values. This is commonly overlooked. PSDefaultParameterValuesThis automatic variable lets you assign default values to any cmdlet without changing the cmdlet. Take a look at this example.
Import-CSV $Path Group-Object -AsHashtable -Property emailThis will add each row into a hashtable and use the specified property as the key to access it. Array as indexer Copying HashtablesOne thing that is important to know is that hashtables are objecs and each variable is just a reference to an object. This just means that it takes a little more work to make a valid copy of a hashtable. Assigning reference typesWhen you have one hashtable and assign it to a second variable, both variables point to the same hashtable.