PowerShell string concatenation gives newlines - string

Question

Note: The actual error from Java/Closure Compiler came from the missing t in --js-outputfile!
I have this PowerShell script:
cls
$jsFiles = #();
Get-ChildItem | Where {$_.PsIsContainer} | Foreach {
$dir = $_.FullName;
$jsFile = $dir + "\" + $_.Name + ".js";
if (Test-Path ($jsFile)) {
$jsFiles += $jsFile;
}
}
$wd = [System.IO.Directory]::GetCurrentDirectory();
# Build Closure Compiler command line call
$cmd = #("-jar $wd\..\ClosureCompiler\compiler.jar");
Foreach ($file in $jsFiles) {
# Both insert a newline!
$cmd += "--js $file";
#$cmd = "$cmd --js $file";
}
$cmd = "$cmd --js_ouput_file $wd\all.js";
Invoke-Expression "java.exe $cmd"
The problem is that newlines are inserted on each += or $cmd = "$cmd str" call!
Echoargs gives me this output:
Arg 0 is <-jar>
Arg 1 is <S:\ome\Path\compiler.jar>
Arg 2 is <--js>
Arg 3 is <S:\ome\Path\script1.js>
Arg 4 is <--js>
Arg 5 is <S:\ome\Path\script2.js>
...
Arg 98 is <--js_ouput_file>
Arg 99 is <S:\ome\Path\all.js>
(Possibly) therefore, I get some errors from java.exe:
java.exe : "--js_ouput_file" is not a valid option
At line:1 char:1
+ java.exe -jar ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: ("--js_ouput_file" is not a valid option:String) [], RemoteException
+ FullyQualifiedErrorId : NativeCommandError

Answer 1

Try to rewrite to much simple version:
cls
$wd = [System.IO.Directory]::GetCurrentDirectory();
# Build Closure Compiler command line call
$cmd = "-jar $wd\..\ClosureCompiler\compiler.jar";
$arrayOfJs = Get-ChildItem -Recurse -Include "*.js" | % { "--js $_.FullName" };
$cmd += [string]::Join(" ", $arrayOfJs);
Invoke-Expression "java $cmd --js_ouput_file $wd\all.js"

Answer 2

When you do
$cmd = #(...);
you are creating an array and hence the subsequent += on it is appending elements to the array and is not string concatenation. Just have it as a string, or before using $cmd. Do something like:
$cmd -join " "
Which will join together the elements into a single space-separated string. By default when the array is coerced into a string, you will see new lines between the elements.