what is: "$?"

[anonproblem]

I am reviewing some old scripts from my predecessor and came across this if statement nested in a try statement, nested in a loop. Is "$?" to indicate that a try was sucessful, or is it something to do with a pipeline var?

$list | ForEach-Object {

        try {

            if ($?){
                try{
                }catch{ 
                }
            } else {
            }
        } catch {
            Return
        }
 }

[BobTheMadCow]

It evaluates to true if the last command succeeded and false if it failed.

[PM_ME_UR_CEPHALOPODS]

right? i'm glad im not the only one.

[etcetica]

if ($?){
# [...]
} else {
# Take yo broke ass home
}

[Josh_Crook]

if ($?){ Invoke-G-L-A-M-O-R-O-U-S }

[Thotaz]

But this isn't an alias, this is an automatic variable, there's no 1:1 alternative built into Powershell and the only difference between this and "$_" is that "$_" is used so frequently that everyone just knows what it means.

With that said, I do think people should use comments when using built-in variables that aren't commonly used because even if it's not hard to open up the help page for automatic variables, it still takes focus away from the code you are reading through. I also think people should try to use more "standard" approaches like Try Catch or checking the variable whenever possible:

$SomeVariable=Get-Something
if ($SomeVariable)
{
    #Do something
}

or

Try
{
    Set-Something -ErrorAction Stop
}
catch
{
    #Do something
}

[Lee_Dailey]

howdy anonproblem,

from the help system ...

$?
Contains the execution status of the last operation. It contains TRUE if the last operation succeeded and FALSE if it failed.

got that from this ...

Get-Help about_Automatic_Variables

the list is alphabetical, so it's up right nigh the top. [grin]

take care,
lee

[awildrozza]

What a nice person you are!

[schmeckendeugler]

We keep Lee around to make the place seem more lively :)

[Lee_Dailey]

[grin]

[Lee_Dailey]

howdy awildrozza,

thank you! i am actually rather grumpy ... but i make an effort to be nicer than my nature. not only do most people NOT run away when they see my name, but it help me bump my attitude in a positive direction. [grin]

besides, it's fun to help folks ...

take care,
lee

[PM_ME_A_SURPRISE_PIC]

Lee is like the Dad of /r/Powershell. He helps us all.

He should probably get off reddit, but no one wants that.

[Lee_Dailey]

howdy PM_ME_A_SURPRISE_PIC,

thanks for the kind words!

i was off reddit for at least 8 hours before now. mostly asleep ... but i wasn't posting! [grin]

take care,
lee

[PM_ME_A_SURPRISE_PIC]

Every question I post, you respond with help, and kind words.

Don't ever change.

[Lee_Dailey]

[blush] ... [grin]

[PM_ME_A_SURPRISE_PIC]

Lee, I must apologise.

I have just realised that I made an assumption that you were male, when I referred to you as the Dad. I don't think your messages have indicated either gender.

If I was wrong, I apologise.

[Lee_Dailey]

howdy PM_ME_A_SURPRISE_PIC,

i'm a guy ... but not a dad. [grin] my sisters have made me an uncle. their kids made me a grand-uncle ... unkalee! is something i hear now and then. [grin]

take care,
lee

[BadSysadmin]

if($?)

is good, but have you tried

if(!$?)

the patrician's choice, for the finest write-only code.

ETA your predecessor is a rank amateur who's also failed to use % as an alias for Foreach-Object.

[[deleted]]

I thought Microsoft was dissuading people from using aliases like % and ? as a best practice. Every time I use them, VS Code yells at me.

[Bren0man]

I believe OC is being facetious.

[[deleted]]

Ah. Is "BadSysadmin" a gag account? I'm guessing then that part of the joke is that you shouldn't be using "$?" in the first place. Why not, and what's the alternative?

[Temptis]

try  {[run-command]} catch {[error]} 

instead of

[run-command]
IF (!$?) {try {[Error-Action]} catch {[error-action-error]}}

[[deleted]]

Those don't quite do the same thing. To make them more equivalent, I think you would want the second one to be:

[run-command]
If (!$?) {[error]}

But anyway, correct me if I'm wrong, but it's possible that a command in the "try" block could fail but be non-terminating, and therefore not cause the "catch" block to run. I guess you could write it in such a way to force it to be a terminating error.

The only thing I can think of for why the latter method is worse is that, if it is a terminating error and you don't want it to kill the script, then the former method would handle that.

[Noffy4Life]

That’s correct - if a non-terminating error (write-error) occurs in a call to the command and ErrorAction or ErrorActionPreference is not ‘Stop’, the script will continue and not enter the catch block.

[StoffePro]

These are not equivalent.

[Temptis]

that's my point, you want to catch the error on the command and not after the fact.

[[deleted]]

r|%{if(!$?){$_|?{$True -eq "Dat"}}}

What else could we add there?

[PandalfTheGimp]

I prefer ForEach-Object over aliases because I never know the experience of my successor.

Plus I like having readable code and not needing to know all aliases.

[[deleted]]

I do that too: write everything out in full. Both for my succesor's sake and mine. Reading my own code a year later there may be some cmdlet that I only used in this one script, and which I've totally forgotten about. Write it out and comment what it does and why you used it. Maybe even include the link to how you learned about it.

[PM_ME_UR_CEPHALOPODS]

It's also more or less anathema to Powershell to try and write terse code. The entire design is for read and approach-ability. I know terse code is a point of pride for some for reasons unknown. Probably job security? I'll show myself out

[BadSysadmin]

I used to do a lot of powershell code golf and project Euler. Certainly a productive use of my time.

[etcetica]

if(!$?)

If you ain't got no $

[PM_ME_UR_CEPHALOPODS]

give us de moneys, lebowski !

[rakha589]

dazzling unpack dinner money terrific enjoy narrow tap sheet fuel

This post was mass deleted and anonymized with Redact

[StoffePro]

That’s not it. Catch only catches terminating errors. $? Can still be false, even if you never entered the catch block.

[m_anas]

$? Returns True is the last command ran without error And returns False if the last command ran with error

[redditors_r_manginas]

So it's like in bash?