PowerShell: Running executable in variable without misinterpetting argument as part of path - powershell

Question

I need to benchmark two different programs on two diferent corpuses, and in order to get more accurate readings, I want to run the benchmark in a loop and take the mean execution time for each benchmark. In order to simplify for myself, I wrote the following PowerShell function:
Function Benchmark {
Param($progPath, $benchmarkPath, $iters=27)
$time = (Measure-Command { & "$progPath" "$benchmarkPath" }).TotalSeconds
$sum = $lowest = $highest = $time
for($i = 1; $i -lt $iters; $i++) {
$time = (Measure-Command { & "$progPath" "$benchmarkPath" }).TotalSeconds
$sum += $time
if($time -lt $lowest) { $lowest = $time }
elseif($time -gt $highest) {$highest = $time }
}
$sum -= ($lowest + $highest)
$sum / ($iters - 2)
}
In theory, this should execute the program supplied as a command in $progPath with the benchmarking script in $benchmarkPath as its argument, but when I run it like this, I get the following result:
PS > $nonPrivateBenchmark = Benchmark(".\Python\PCbuild\amd64\python", ".\Benchmarks\non_private_access.py")
& : The term '.\Python\PCbuild\amd64\python .\Benchmarks\non_private_access.py' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify that the path is correct and try again.
At line:3 char:30
+ $time = (Measure-Command { & "$progPath" "$benchmarkPath" }).TotalSeconds
+ ~~~~~~~~~~~
+ CategoryInfo : ObjectNotFound: (.\Python\PCbuil...ivate_access.py:String) [], CommandNotFoundException
+ FullyQualifiedErrorId : CommandNotFoundException
(Plus 26 repetitions of the same error but on line 6.)
However, if assign the three parameter arguments and copy the remaining function body directly into PowerShell, it works and sets $nonPrivateAccess to a reasonable value:
$progPath = ".\Python\PCbuild\amd64\python"
$benchmarkPath = ".\Benchmarks\non_private_access.py"
$iters = 27
$time = (Measure-Command { & "$progPath" "$benchmarkPath" }).TotalSeconds
$sum = $lowest = $highest = $time
for($i = 1; $i -lt $iters; $i++) {
$time = (Measure-Command { & "$progPath" "$benchmarkPath" }).TotalSeconds
$sum += $time
if($time -lt $lowest) { $lowest = $time }
elseif($time -gt $highest) {$highest = $time }
}
$sum -= ($lowest + $highest)
$nonPrivateBenchmark = $sum / ($iters - 2)
I have through experimentation concluded that the problem is that "$progPath" "$benchmarkPath" is concatenated into the single string '.\Python\PCbuild\amd64\python .\Benchmarks\non_private_access.py' before executed with the & operator, and the space separating them is interpretted as a part of the command name, making PowerShell try to execute the entire string as a single command (which can't be executed). I have tried putting escaped quotes both around and inside the argument parameter, but to no avail. Does anyone else have a solution to this problem?
PS:
Quite extensive searching has only given me a lot of hits with people having the opposite problem. Could it be that I have some non-default PowerShell settings activated making it parse the spaces overly aggressively?

Answer 1

Benchmark(".\Python\PCbuild\amd64\python", ".\Benchmarks\non_private_access.py")
This syntax is passing an array to the first parameter of your Benchmark function, which then gets converted to a single string when it's used as a command. This is effectively the same as:
Benchmark ".\Python\PCbuild\amd64\python", ".\Benchmarks\non_private_access.py"
The normal syntax for passing multiple parameters to a PowerShell function is to place a space between the parameters:
Benchmark ".\Python\PCbuild\amd64\python" ".\Benchmarks\non_private_access.py"
You can also use the parameter names:
Benchmark -progPath ".\Python\PCbuild\amd64\python" -benchmarkPath ".\Benchmarks\non_private_access.py"