Operator not Recognized with Invoke-Expression in PowerShell

Question

I am trying to run the docker command in a PowerShell script and test if the command was not successful, but I am failing to do so. I am using:

if (!Invoke-Expression -Command docker ps -q -f name=php72) {
    #some other code here
}

The error that I get after running this is:

Line |
  31 |  if (!Invoke-Expression -Command docker ps -q -f name=php72) {
     |      ~~~~~~~~~~~~~~~~~~
     | The term '!Invoke-Expression' 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.

I have tried the -not operator to no avail as well.

avarice · Accepted Answer · 2020-10-18 02:33:43Z

2

Add another bracket:

if (!(Invoke-Expression -Command docker ps -q -f name=php72)){
    #some other code here
}

Unless here !Invoke-Expression is evaluated, which is invalid.

Best way is to use like this:

docker ps -q -f name=php72 >$null 2>&1
if($lastExitCode -eq 1){"FAILED!"}

answered Oct 18, 2020 at 2:33

avarice

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marsze · Accepted Answer · 2020-10-18 09:53:42Z

1

Your syntax is invalid. PowerShell has 2 parsing modes: Expression and argument. The latter is the one where you work with commands. There, the name of the command (e.g. Invoke-Expression) must always come first.

In short: you have to wrap the command either with the grouping opterator () or subexpression operator $() to use it inside an expression:

-not (Invoke-Expression ...)
# or
-not $(Invoke-Expression ...)

(-not and ! work exactly the same)

But as @WasifHasan pointed out, docker is an external program, so the best way to check for success is using the $? automatic variable, which will be $false if $LASTEXITCODE is any other value than 0:

docker ps -q -f name=php72 2>&1>$null
if ($?} {
    # your other code here
}

edited Oct 18, 2020 at 9:53

answered Oct 18, 2020 at 9:42

marsze

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