How to tell PowerShell to wait for each command to

问题:

I have a PowerShell 1.0 script to just open a bunch of applications. The first is a virtual machine and the others are development applications. I want the virtual machine to finish booting before the rest of the applications are opened.

In bash I could just say "cmd1 && cmd2"

This is what I've got...

C:\Applications\VirtualBox\vboxmanage startvm superdooper
    &"C:\Applications\NetBeans 6.5\bin\netbeans.exe"

回答1:

Normally, for internal commands PowerShell does wait before starting the next command. One exception to this rule is external Windows subsystem based EXE. The first trick is to pipeline to Out-Null like so:

Notepad.exe | Out-Null

PowerShell will wait until the Notepad.exe process has been exited before continuing. That is nifty but kind of subtle to pick up from reading the code. You can also use Start-Process with the -Wait parameter:

Start-Process <path to exe> -NoNewWindow -Wait

If you are using the PowerShell Community Extensions version it is:

$proc = Start-Process <path to exe> -NoNewWindow -PassThru
$proc.WaitForExit()

Another option in PowerShell 2.0 is to use a background job:

$job = Start-Job { invoke command here }
Wait-Job $job
Receive-Job $job

回答2:

Besides using Start-Process -Wait, piping the output of an executable will make Powershell wait. Depending on the need, I will typically pipe to Out-Null, Out-Default, Out-String or Out-String -Stream. Here is a long list of some other output options.

# Saving output as a string to a variable.
$output = ping.exe example.com | Out-String

# Filtering the output.
ping stackoverflow.com | where { $_ -match '^reply' }

# Using Start-Process affords the most control.
Start-Process -Wait SomeExecutable.com

I do miss the CMD/Bash style operators that you referenced (&, &&, ||). It seems we have to be more verbose with Powershell.

回答3:

Just use "Wait-process" :

"notepad","calc","wmplayer" | ForEach-Object {Start-Process $_} | Wait-Process ;dir

job is done

回答4:

If you use Start-Process <path to exe> -NoNewWindow -Wait

You can also use the -PassThru option to echo output.

回答5:

Some programs can't process output stream very well, using pipe to Out-Null may not block it.
And Start-Process needs the -ArgumentList switch to pass arguments, not so convenient.
There is also another approach.

$exitCode = [Diagnostics.Process]::Start(<process>,<arguments>).WaitForExit(<timeout>)

回答6:

Including the option -NoNewWindow gives me an error: Start-Process : This command cannot be executed due to the error: Access is denied.

The only way I could get it to work was to call:

Start-Process <path to exe> -Wait

回答7:

Taking it further you could even parse on the fly

e.g.

& "my.exe" | %{
    if ($_ -match 'OK')
    { Write-Host $_ -f Green }
    else if ($_ -match 'FAIL|ERROR')
    { Write-Host $_ -f Red }
    else 
    { Write-Host $_ }
}

回答8:

There's always cmd. It may be less annoying if you have trouble quoting arguments to start-process:

cmd /c start /wait notepad