I'm trying to start a job that creates a file. But it doesn't.
here's the very simple code:
start-job -ScriptBlock { "hi" | set-content "hi.txt" }
The file "hi.txt" never gets created.
Why not?
It is most likely creating the file, just not where you expect because you used a relative path. Try executing this to see where the file is going:
Start-Job {$pwd} | Receive-Job -Wait
Better yet, use an absolute path:
Start-Job { 'hi' > c:\hi.txt }
Or pass in the desired path:
Start-Job {param($path) 'hi' > "$path\hi.txt"} -arg $pwd
Related
Inside a powershell script, I'm running a command which starts a new powershell as admin (if I'm not and if needed, depending on $arg) and then runs the script.
I'm trying to redirect stdout and stderr to the first terminal.
Not trying to make things easier, there are arguments too.
param([string]$arg="help")
if($arg -eq "start" -Or $arg -eq "stop")
{
if().groups -match "S-1-5-32-544"))
{
Start-Process powershell -Verb runas -ArgumentList " -file servicemssql.ps1 $arg"
exit
}
}
$Services = "MSSQLSERVER", "SQLSERVERAGENT", "MSSQLServerOLAPService", "SSASTELEMETRY", "SQLBrowser", `
"SQLTELEMETRY", "MSSQLLaunchpad", "SQLWriter", "MSSQLFDLauncher"
function startsql {
"starting SQL services"
Foreach ($s in $Services) {
"starting $s"
Start-Service -Name "$s"
}
}
function stopsql {
"stopping SQL services"
Foreach ($s in $Services) {
"stopping $s"
Stop-Service -Force -Name "$s"
}
}
function statussql {
"getting SQL services status"
Foreach ($s in $Services) {
Get-Service -Name "$s"
}
}
function help {
"usage: StartMssql [status|start|stop]"
}
Switch ($arg) {
"start" { startsql }
"stop" { stopsql }
"status" { statussql }
"help" { help }
"h" { help }
}
Using the following answers on SO doesn't work:
Capturing standard out and error with Start-Process
Powershell: Capturing standard out and error with Process object
How to deal with the double quote inside double quote while preserving the variable ($arg) expansion ?
PowerShell's Start-Process cmdlet:
does have -RedirectStandardOut and -RedirectStandardError parameters,
but syntactically they cannot be combined with -Verb Runas, the argument required to start a process elevated (with administrative privileges).
This constraint is also reflected in the underlying .NET API, where setting the .UseShellExecute property on a System.Diagnostics.ProcessStartInfo instance to true - the prerequisite for being able to use .Verb = "RunAs" in order to run elevated - means that you cannot use the .RedirectStandardOutput and .RedirectStandardError properties.
Overall, this suggests that you cannot directly capture an elevated process' output streams from a non-elevated process.
A pure PowerShell workaround is not trivial:
param([string] $arg='help')
if ($arg -in 'start', 'stop') {
if (-not (([System.Security.Principal.WindowsPrincipal] [System.Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole('Administrators'))) {
# Invoke the script via -Command rather than -File, so that
# a redirection can be specified.
$passThruArgs = '-command', '&', 'servicemssql.ps1', $arg, '*>', "`"$PSScriptRoot\out.txt`""
Start-Process powershell -Wait -Verb RunAs -ArgumentList $passThruArgs
# Retrieve the captured output streams here:
Get-Content "$PSScriptRoot\out.txt"
exit
}
}
# ...
Instead of -File, -Command is used to invoke the script, because that allows appending a redirection to the command: *> redirects all output streams.
#soleil suggests using Tee-Object as an alternative so that the output produced by the elevated process is not only captured, but also printed to the (invariably new window's) console as it is being produced:
..., $arg, '|', 'Tee-Object', '-FilePath', "`"$PSScriptRoot\out.txt`""
Caveat: While it doesn't make a difference in this simple case, it's important to know that arguments are parsed differently between -File and -Command modes; in a nutshell, with -File, the arguments following the script name are treated as literals, whereas the arguments following -Command form a command that is evaluated according to normal PowerShell rules in the target session, which has implications for escaping, for instance; notably, values with embedded spaces must be surrounded with quotes as part of the value.
The $PSScriptRoot\ path component in output-capture file $PSScriptRoot\out.txt ensures that the file is created in the same folder as the calling script (elevated processes default to $env:SystemRoot\System32 as the working dir.)
Similarly, this means that script file servicemssql.ps1, if it is invoked without a path component, must be in one of the directories listed in $env:PATH in order for the elevated PowerShell instance to find it; otherwise, a full path is also required, such as $PSScriptRoot\servicemssql.ps1.
-Wait ensures that control doesn't return until the elevated process has exited, at which point file $PSScriptRoot\out.txt can be examined.
As for the follow-up question:
To go even further, could we have a way to have the admin shell running non visible, and read the file as we go with the Unix equivalent of tail -f from the non -privileged shell ?
It is possible to run the elevated process itself invisibly, but note that you'll still get the UAC confirmation prompt. (If you were to turn UAC off (not recommended), you could use Start-Process -NoNewWindow to run the process in the same window.)
To also monitor output as it is being produced, tail -f-style, a PowerShell-only solution is both nontrivial and not the most efficient; to wit:
param([string]$arg='help')
if ($arg -in 'start', 'stop') {
if (-not (([System.Security.Principal.WindowsPrincipal] [System.Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole('Administrators'))) {
# Delete any old capture file.
$captureFile = "$PSScriptRoot\out.txt"
Remove-Item -ErrorAction Ignore $captureFile
# Start the elevated process *hidden and asynchronously*, passing
# a [System.Diagnostics.Process] instance representing the new process out, which can be used
# to monitor the process
$passThruArgs = '-noprofile', '-command', '&', "servicemssql.ps1", $arg, '*>', $captureFile
$ps = Start-Process powershell -WindowStyle Hidden -PassThru -Verb RunAs -ArgumentList $passThruArgs
# Wait for the capture file to appear, so we can start
# "tailing" it.
While (-not $ps.HasExited -and -not (Test-Path -LiteralPath $captureFile)) {
Start-Sleep -Milliseconds 100
}
# Start an aux. background that removes the capture file when the elevated
# process exits. This will make Get-Content -Wait below stop waiting.
$jb = Start-Job {
# Wait for the process to exit.
# Note: $using:ps cannot be used directly, because, due to
# serialization/deserialization, it is not a live object.
$ps = (Get-Process -Id $using:ps.Id)
while (-not $ps.HasExited) { Start-Sleep -Milliseconds 100 }
# Get-Content -Wait only checks once every second, so we must make
# sure that it has seen the latest content before we delete the file.
Start-Sleep -Milliseconds 1100
# Delete the file, which will make Get-Content -Wait exit (with an error).
Remove-Item -LiteralPath $using:captureFile
}
# Output the content of $captureFile and wait for new content to appear
# (-Wait), similar to tail -f.
# `-OutVariable capturedLines` collects all output in
# variable $capturedLines for later inspection.
Get-Content -ErrorAction SilentlyContinue -Wait -OutVariable capturedLines -LiteralPath $captureFile
Remove-Job -Force $jb # Remove the aux. job
Write-Verbose -Verbose "$($capturedLines.Count) line(s) captured."
exit
}
}
# ...
Is there any way to run parallel programmed functions in PowerShell?
Something like:
Function BuildParallel($configuration)
{
$buildJob = {
param($configuration)
Write-Host "Building with configuration $configuration."
RunBuilder $configuration;
}
$unitJob = {
param()
Write-Host "Running unit."
RunUnitTests;
}
Start-Job $buildJob -ArgumentList $configuration
Start-Job $unitJob
While (Get-Job -State "Running")
{
Start-Sleep 1
}
Get-Job | Receive-Job
Get-Job | Remove-Job
}
Does not work because it complains about not recognizing "RunUnitTests" and "RunBuilder", which are functions declared in the same script file. Apparently this happens because the script block is a new context and does not know anything about the scripts declared in the same file.
I could try to use -InitializationScript in Start-Job, but both RunUnitTests and RunBuilder call more functions declared in the same file or referred from other files, so...
I'm sure there's a way to do this, since it's just modular programming (functions, routines and all that stuff).
You could have the functions in a separate file and import them into the current context wherever needed via dot sourcing. I do this in my Powershell profile, so some of my custom functions are available.
$items = Get-ChildItem "$PSprofilePath\functions"
$items | ForEach-Object {
. $_.FullName
}
If you wanted import one file, it would just be:
. C:\some\path\RunUnitTests.ps1
I have this snippet of code
$actDate=Get-Date -Format 'yyyy-MM-dd'
Start-job -name "FMLE" -command { cmd.exe /c 'c:\Program Files (x86)\Adobe\Flash Media Live Encoder 3.2\FMLEcmd.exe' /p C:\tasks\testing_2\testing 2_$actDate.xml /ap username:password /ab username:password /l C:\Users\acruz\AppData\Local\Temp\temp.log }
I know for sure, that the var $actDate is not being replaced at the line, how shuld I do that?
My two questions are: how to replace the $actDate for its value and how to save the result of the job to one log
Thanks for your help
EDIT
This does not works either:
$actDate = (Get-Date -Format 'yyyy-MM-dd')
$Args = ("/p C:\tasks\testing_2\testing 2_$actDate.xml","/ap username:password", "/ab uysername:password", "/l C:\Users\acruz\AppData\Local\Temp\temp.log")
$Args
$j = Start-job -name "FMLE" -ScriptBlock { & 'c:\Program Files (x86)\Adobe\Flash Media Live Encoder 3.2\FMLEcmd.exe' #args } -ArgumentList $args
Get-Job $j.Id
Receive-Job -Job $j | Out-File 'C:\Users\acruz\AppData\Local\Temp\temp.log' -encoding ASCII -append -force
Although $Args has the right information...
For your first question, you need to include the path using double quotes. A suggestion if you can then remove the space in the testing 2
"C:\tasks\testing_2\testing2_$actDate.xml"
To log result of the job use Receive-Job cmdlet.
One more try:
Try to put all paths in double quotes and then surround everything with a single quote after the cmd.exe /c part as shown below. Try to achieve something simpler with a simple task and then try to add complexity
$job = Start-Job -name "Hel" -Command { cmd.exe /c '"C:\Program Files (x86)\Mozilla Firefox\firefox.exe" /?'}
I was able to make it work by doing it like this:
Start-job -Verbose -ScriptBlock {
$actDate = Get-Date -Format yyyy-MM-dd
cd "c:\Program Files (x86)\Adobe\Flash Media Live Encoder 3.2\"
.\FMLEcmd.exe /p "C:\site.com.mx\tasks\test_23445678\test 23445678_$actDate.xml" /ap user:password /ab user:password /l C:\site.com.mx\task.log
}
By doing it with -command it does not work, cause it does not replace the variable at all. Also, if I do it with -ArgumentList either was replacing the variable $actDate, so I though that may be by adding the whole script within the block it was work... and indeed, it did it...
So I don't know why it does not works, but this is a fix for me.
I have the following job in powershell:
$job = start-job {
...
c:\utils\MyToolReturningSomeExitCode.cmd
} -ArgumentList $JobFile
How do I access the exit code returned by c:\utils\MyToolReturningSomeExitCode.cmd ? I have tried several options, but the only one I could find that works is this:
$job = start-job {
...
c:\utils\MyToolReturningSomeExitCode.cmd
$LASTEXITCODE
} -ArgumentList $JobFile
...
# collect the output
$exitCode = $job | Wait-Job | Receive-Job -ErrorAction SilentlyContinue
# output all, except the last line
$exitCode[0..($exitCode.Length - 2)]
# the last line is the exit code
exit $exitCode[-1]
I find this approach too wry to my delicate taste. Can anyone suggest a nicer solution?
Important, I have read in the documentation that powershell must be run as administrator in order for the job related remoting stuff to work. I cannot run it as administrator, hence -ErrorAction SilentlyContinue. So, I am looking for solutions not requiring admin privileges.
Thanks.
If all you need is to do something in background while the main script does something else then PowerShell class is enough (and it is normally faster). Besides it allows passing in a live object in order to return something in addition to output via parameters.
$code = #{}
$job = [PowerShell]::Create().AddScript({
param($JobFile, $Result)
cmd /c exit 42
$Result.Value = $LASTEXITCODE
'some output'
}).AddArgument($JobFile).AddArgument($code)
# start thee job
$async = $job.BeginInvoke()
# do some other work while $job is working
#.....
# end the job, get results
$job.EndInvoke($async)
# the exit code is $code.Value
"Code = $($code.Value)"
UPDATE
The original code was with [ref] object. It works in PS V3 CTP2 but does not work in V2. So I corrected it, we can use other objects instead, a hashtable, for example, in order to return some data via parameters.
One way you can detect if the background job failed or not based on an exit code is to evaluate the exit code inside the background job itself and throw an exception if the exit code indicates an error occurred. For instance, consider the following example:
$job = start-job {
# ...
$output = & C:\utils\MyToolReturningSomeExitCode.cmd 2>&1
if ($LASTEXITCODE -ne 0) {
throw "Job failed. The error was: {0}." -f ([string] $output)
}
} -ArgumentList $JobFile
$myJob = Start-Job -ScriptBlock $job | Wait-Job
if ($myJob.State -eq 'Failed') {
Receive-Job -Job $myJob
}
A couple things of note in this example. I am redirecting the standard error output stream to the standard output stream to capture all textual output from the batch script and returning it if the exit code is non-zero indicating it failed to run. By throwing an exception this way the background job object State property will let us know the result of the job.
I have a file template.txt which contains the following:
Hello ${something}
I would like to create a PowerShell script that reads the file and expands the variables in the template, i.e.
$something = "World"
$template = Get-Content template.txt
# replace $something in template file with current value
# of variable in script -> get Hello World
How could I do this?
Another option is to use ExpandString() e.g.:
$expanded = $ExecutionContext.InvokeCommand.ExpandString($template)
Invoke-Expression will also work. However be careful. Both of these options are capable of executing arbitrary code e.g.:
# Contents of file template.txt
"EvilString";$(remove-item -whatif c:\ -r -force -confirm:$false -ea 0)
$template = gc template.txt
iex $template # could result in a bad day
If you want to have a "safe" string eval without the potential to accidentally run code then you can combine PowerShell jobs and restricted runspaces to do just that e.g.:
PS> $InitSB = {$ExecutionContext.SessionState.Applications.Clear(); $ExecutionContext.SessionState.Scripts.Clear(); Get-Command | %{$_.Visibility = 'Private'}}
PS> $SafeStringEvalSB = {param($str) $str}
PS> $job = Start-Job -Init $InitSB -ScriptBlock $SafeStringEvalSB -ArgumentList '$foo (Notepad.exe) bar'
PS> Wait-Job $job > $null
PS> Receive-Job $job
$foo (Notepad.exe) bar
Now if you attempt to use an expression in the string that uses a cmdlet, this will not execute the command:
PS> $job = Start-Job -Init $InitSB -ScriptBlock $SafeStringEvalSB -ArgumentList '$foo $(Start-Process Notepad.exe) bar'
PS> Wait-Job $job > $null
PS> Receive-Job $job
$foo $(Start-Process Notepad.exe) bar
If you would like to see a failure if a command is attempted, then use $ExecutionContext.InvokeCommand.ExpandString to expand the $str parameter.
I've found this solution:
$something = "World"
$template = Get-Content template.txt
$expanded = Invoke-Expression "`"$template`""
$expanded
Since I really don't like the idea of One More Thing To Remember - in this case, remembering that PS will evaluate variables and run any commands included in the template - I found another way to do this.
Instead of variables in template file, make up your own tokens - if you're not processing HTML, you can use e.g. <variable>, like so:
Hello <something>
Basically use any token that will be unique.
Then in your PS script, use:
$something = "World"
$template = Get-Content template.txt -Raw
# replace <something> in template file with current value
# of variable in script -> get Hello World
$template=$template.Replace("<something>",$something)
It's more cumbersome than straight-up InvokeCommand, but it's clearer than setting up limited execution environment just to avoid a security risk when processing simple template. YMMV depending on requirements :-)