While using powershell I struggle to build up a filename from two variables. When I originally creaded the powershell script, it was working fine. Now I have tried to move some repeatable steps into a function, but the string behaviour is different.
MWE:
$topa = "ABC"
$topb = "XYZ"
function Test-Fun{
param(
$a,
$b
)
echo "$($a)H$($b).csv"
}
echo "$($topa)H$($topb).csv"
Test-Fun($topa, $topb)
The output on my system is
ABCHXYZ.csv
ABC XYZH.csv
Originally, I wanted to use an underscore instead of H and thought that is causing issues, but its not. What did I miss or rather what is the difference between string expansion within a function and outside of it?
You are calling Test-Func wrong. The comma after $topa will create an array, so you basically pass []"ABC", "XYZ" as an array to $a. In that case $b is empty!
You can easily fix this by removing the comma (also the parentheses are not necessary):
Test-Fun $topa $topb
Related
I'm learning PowerShell so please forgive (what I'm sure is) a simple question.
I'm used to coding BATCH scripts and if I wanted to merge %USERDOMAIN% and %USERNAME% I would:
set zFullUsername=%USERDOMAIN%\%USERNAME%
echo %zFullUsername%
How can I do the same in PowerShell?
Thank you for your time.
On a supported Operating System, I wouldn't even bother with environment variables for this:
$zFullUsername = whoami
Then just access it as required:
$zFullUsername
In PowerShell, you can access environment variables in a few different ways. The way I recommend is to use the $env:VAR variable to access them.
$user = $env:USERNAME
$domain = $env:USERDOMAIN
echo "$domain\$user"
Note: \ is not an escape character in the PowerShell parser, ` is.
Similarly to rendering the echo command (echo is an alias of Write-Output btw) you can create a username variable like so:
$fullUserName = "$domain\$user"
Or you can skip right to creating $fullUserName straight from the environment variables:
$fullUserName = "${env:USERDOMAIN}\${env:USERNAME}"
Note: When variables have non-alphanumeric characters in them, the ${} sequence tells PowerShell everything between the ${} is part of the variable name to expand.
It seems the : in $env:VAR is actually an exception to this rule, as"Username: $env:USERNAME" does render correctly. So the ${} sequence above is optional.
To avoid confusion when trying to apply this answer in other areas, if you needed to insert the value of an object property or some other expression within a string itself, you would use a sub-expression within the string instead, which is the $() sequence:
$someVar = "Name: $($someObject.Name)"
When using either ${} or $(), whitespace is not allowed to pad the outer {} or ().
I know I can dot source a file:
. .\MyFunctions.ps1
But, I would like to dot source the commands in a string variable:
. $myFuctions
I see that this is possible:
.{$x=2}
And $x equals 2 after the script block is sourced.
But... .{$myFunctions} does not work.
I tried $myFunctions | Invoke-Expression, but it doesn't keep the source function in the current scope. The closest I have been able to come up with is to write the variable to a temporary file, dot source the file, and then remove the file.
Inevitably, someone will ask: "What are you trying to do?" So here is my use case:
I want to obfuscate some functions I intend to call from another script. I don't want to obfuscate the master script, just my additional functions. I have a user base that will need to adjust the master script to their network, directory structure and other local factors, but I don't want certain functions modified. I would also like to protect the source code. So, an alternate question would be: What are some good ways to protect PowerShell script code?
I started with the idea that PowerShell will execute a Base64-encoded string, but only when passed on the command line with -EncodedCommand.
I first wanted to dot source an encoded command, but I couldn't figure that out. I then decided that it would be "obfuscated" enough for my purposes if I converted by Base64 file into a decode string and dot sourced the value of the string variable. However, without writing the decoded source to a file, I cannot figure out how to dot source it.
It would satisfy my needs if I could Import-Module -EncodedCommand .\MyEncodedFile.dat
Actually, there is a way to achieve that and you were almost there.
First, as you already stated, the source or dot operator works either by providing a path (as string) or a script block. See also: . (source or dot operator).
So, when trying to dot-source a string variable, PowerShell thinks it is a path. But, thanks to the possibility of dot-sourcing script blocks, you could do the following:
# Make sure everything is properly escaped.
$MyFunctions = "function Test-DotSourcing { Write-Host `"Worked`" }"
. { Invoke-Expression $MyFunctions }
Test-DotSourcing
And you successfully dot-sourced your functions from a string variable!
Explanation:
With Invoke-Expression the string is evaluated and run in the child scope (script block).
Then with . the evaluated expressions are added to the current scope.
See also:
Invoke-Expression
About scopes
While #dwettstein's answer is a viable approach using Invoke-Expression to handle the fact that the function is stored as a string, there are other approaches that seem to achieve the same result below.
One thing I'm not crystal clear on is the scoping itself, Invoke-Expression doesn't create a new scope so there isn't exactly a need to dot source at that point...
#Define your function as a string
PS> $MyUselessFunction = "function Test-WriteSomething { 'It works!' }"
#Invoke-Expression would let you use the function
PS> Invoke-Expression $MyUselessFunction
PS> Test-WriteSomething
It works!
#Dot sourcing works fine if you use a script block
PS> $ScriptBlock = [ScriptBlock]::Create($MyUselessFunction)
PS> . $ScriptBlock
PS> Test-WriteSomething
It works!
#Or just create the function as a script block initially
PS> $MyUselessFunction = {function Test-WriteSomething { 'It works!' }}
PS> . $MyUselessFunction
PS> Test-WriteSomething
It works!
In other words, there are probably a myriad of ways to get something similar to what you want - some of them documented, and some of them divined from the existing documentation. If your functions are defined as strings, then Invoke-Expression might be needed, or you can convert them into script blocks and dot source them.
At this time it is not possible to dot source a string variable.
I stand corrected! . { Invoke-Expression $MyFunctions } definitely works!
Can any of you let me know how to state a variable in a PowerShell line? Just like I could do using PowerShell ISE I would like to be able to do so via the plain console.
You can assign values to a PowerShell variable by combining a variable name, an assignment operator, and an expression. Here is a simple example:
>> $a = 1 + 1
If you want to populate multiple variables with the same value, you can save some typing as in the example below:
>> $a = $b = $c = 1
You can also define multiple variables with different values on one line:
>> $a, $b, $c = 1, 2, 3
To display the value of a variable, you don’t need a special command as in many other programming languages; entering the variable name is enough. This works in a script and on a command prompt.
>> $c
To take values from user, similar to Python input() function you can use:
$Number = Read-Host "Please enter a number"
Read the official documentation here.
I finally found the solution to get the job done. I just set the variable and end it with a semi-colon. Then I can go on with scripting.
Thank you all.
I've been searching all over the place and since I'm taking my first steps in PERL this might be one of he dumbest questions but here it goes.
So I'm creating a script to manage my windows and later bind it to keyboard shortcuts, so I I'm trying to run a command and passing some variables:
my $command = `wmctrl -r :ACTIVE: -e 0,0,0,$monitors->{1}->{'width'}/2,$monitors->{1}->{'height'}`;
But I get an error saying I'm not passing the right parameters to the command, but if I do this, everything works great:
my $test = $monitors->{1}->{'width'}/2;
my $command = `wmctrl -r :ACTIVE: -e 0,0,0,$test,$monitors->{1}->{'height'}`;
So do I really have to do this? assign it first to a variable and then pass it, or there's a more elegant way of doing it?
The backticks operator (or the qx{}) accepts A string which is (possibly) interpolated. So accepts string and not expression like $var/2.
Thats mean than the $variables ($var->{1}->{some} too) are expanded but not the arithmetic expressions.
Therefore your 2 step variant works, but not the first.
If you want evaluate an expression inside the string you can use the next:
my $ans=42;
print "The #{[ $ans/2 ]} is only the half of answer\n";
prints
The 21 is only the half of answer
but it is not very readable, so better and elegant is what you're already doing - calculate the command argument in andvace, and to the qx{} or backticks only pass the calculated $variables.
I've got the following code:
function printVars($var1, $var2)
{
Write-Host "var1: $var1"
Write-Host "var2: $var2"
}
printVars ('asdf', 'qwer')
It produces this result:
var1: asdf qwer
var2:
I am expecting this:
var1: asdf
var2: qwer
Why is it doing that and how do I get it to do what I want?
Because ('asdf','qwer') gets treated as an array, so $var1 gets the array and $var2 is empty.
Do printVars 'asdf' 'qwer'
Even if you don't have the parantheses and have just the comma, it is an array.
Try this:
$b ="one","two"
$b.GetType()
The correct answer has already been provided but for those looking for further information I tore this off my PowerShell quick reference chart. This assumes function f's signature is f($a, $b, $c):
Thus, one can call a function with space-separated positional parameters or order-independent named parameters. The other pitfalls reveal that you need to be cognizant of commas, parentheses, and white space.
For further reading see my recent article Down the Rabbit Hole- A Study in PowerShell Pipelines, Functions, and Parameters just published on Simple-Talk.com. The article contains a link to the quick reference/wall chart as well.
I see now. I'm calling the function wrong.
It should be this:
printVars 'asdf' 'qwer'
The quotes could be removed too.
Although it looks like the brace-languages like Perl and C calling a function is like calling another command using most shells.
When I put the comma in there it appends the strings together into one string and passes that as the first argument.