I am trying to compare two dates and decide based on the number of hours gap but the comparison doesn't seem to work. I tried to cast TotalHours to [int] but no luck. What it surprises me is that I get the same result using -gt or -lt.... :?
it must be something simple but I dont see it.
here the code
$stamp = "14/11/2015 14:20:57"
$rightNow = Get-Date
$stampDateTime = [datetime]::ParseExact($stamp,'dd/MM/yyyy HH:mm:ss',[Globalization.CultureInfo]::InvariantCulture)
$difference = NEW-TIMESPAN –Start $stampDateTime –End $rightNow
if ([int]$difference.TotalHours -gt 24 ) { $ok = "OK" }
if ($ok){
Write-Host "VALID"
}else{
Write-Host "BAD"
}
Your if ($ok) is the issue. All strings when evaluated as booleans will return true.
Changing it so that you are using boolean would be one way to address it.
if ([int]$difference.TotalHours -gt 24 ) { $ok = $true }
if ($ok){
Write-Host "VALID"
}else{
Write-Host "BAD"
}
You should also set a known value at the beginning of the script to use as a flag. This is important as the variable state will persist between executions in a PowerShell session.
# assume false
$ok = $false
Depending on your needs you don't need to keep this logic. You can bypass the second if all together because as presented it is redundant.
if ([int]$difference.TotalHours -gt 24 ) {
Write-Host "VALID"
}else{
Write-Host "BAD"
}
I understand this might just be the simple example you used to make the question.
Consider the following to understand what happened. Any non-zero length string will resolve to $true when cast as a boolean.
PS C:\> [boolean]"OK"
True
PS C:\> [boolean]"VeryBad"
True
PS C:\> [boolean]""
False
Related
I am trying to test Time out after 30 seconds.
Sample code:
$a = "y"
$b = "n"
$timeout = New-TimeSpan -Seconds 30
$stopwatch = [System.Diagnostics.Stopwatch]::StartNew()
$stopwatch.Start()
$timeout.Seconds
$stopwatch.elapsed.Seconds
do{
if($a -eq "n"){
Write-Host "This block will never run"
break
}
if($stopwatch.elapsed.Seconds -lt $timeout.Seconds){
Write-Host "Testing this block: Time OUT!!"
break
}
}while($a -eq $b)
$stopwatch.Stop()
But the if block if($stopwatch.elapsed.Seconds -lt $timeout.Seconds) is true even $stopwatch.elapsed.Seconds value is 0 and $timeout.Seconds value is 30 in the loop and complete the code in few milliseconds and not taking 30 seconds to print the Time out statement.
Could anyone please give me pointer to resolve this issue.
A couple of things:
You don't need these two lines: $timeout.Seconds and $stopwatch.elapsed.Seconds above the loop
Your while condition should be while($a -ne $b)
The test inside the loop should read if($stopwatch.elapsed.Seconds -ge $timeout.Seconds)
Try
$a = "y"
$b = "n"
$timeout = New-TimeSpan -Seconds 30
$stopwatch = [System.Diagnostics.Stopwatch]::new()
$stopwatch.Start()
do {
if($stopwatch.Elapsed.Seconds -ge $timeout.Seconds){
Write-Host "Testing this block: Time OUT!!"
break
}
# no timeout, so proceed with what needs to be done here
# . . .
} while($a -ne $b) # loop forever unless you set $a equal to $b in the loop somewhere
$stopwatch.Stop()
Theo's helpful answer addresses incidental logic problems with your approach and offers a solution that probably will work, but isn't fully robust: If the activity in your loop exceeds 1 minute before the timeout condition is tested, the test won't work as intended (even with the logic problems fixed).
You have two options:
Use .TotalSeconds instead of .Seconds, for the reasons explained below.
More simply, taking advantage of the fact that [timespan] instances are directly comparable (see below), you can use:
if ($stopwatch.elapsed -gt $timeout) { # ...
As zett42 points out, [timespan] instances are directly comparable, due to implementing the .NET System.IComparable interface (as well as its generic counterpart); e.g.:
# -> $true - a timespan representing a 61-second duration
# is greater than one representing a 60-second (1-minute) duration.
[timespan]::FromSeconds(61) -gt [timespan] '00:01:00'
Therefore, as shown in the top section, you can simply directly compare $stopwatch.elapsed and $timeout - both of which are [timespan] instances.
The .Seconds property of a [timespan] instance is only the seconds component, potentially alongside larger units, such as minutes (.Minutes) and hours (.Hours)
You need the .TotalSeconds property to get the total amount of seconds (analogously, there are also .TotalDays, .TotalHours, and .TotalMinutes properties).
Also note that .Seconds is always a whole number ([int]), whereas .TotalSeconds can be a fractional value ([double]).
To illustrate the difference:
PS> [timespan] '00:01:05' | # 1 minute and 5 seconds
Select-Object Seconds, TotalSeconds
Seconds TotalSeconds
------- ------------
5 65
#sivam The issue is-
You're not applying the proper properties of the timespan command if it goes beyond 59 seconds then at 60 seconds it will consider it 1 minute.
Update the condition inside the loop if($stopwatch.elapsed.Seconds -lt $timeout.Seconds)
Try
$a = "y"
$b = "n"
$timeout = New-TimeSpan -Minutes 1
$stopwatch = [System.Diagnostics.Stopwatch]::StartNew()
$stopwatch.Start()
$timeout.Minutes
$stopwatch.elapsed.Minutes
do{
if($a -eq "n"){
Write-Host "This block will never run"
break
}
if($stopwatch.elapsed.Minutes -ge $timeout.Minutes){
Write-Host "Time OUT!!"
break
}
}while($a -ne $b)
$stopwatch.Stop()
I'm having a little trouble with a PS script right now.
What I am trying to do:
Depending on which OU a computer belongs to, it should get a different printer mapped.
I am trying this with a switch condition, but regardless of what I try the condition seems to be always TRUE (although I know it isn't)
When I type in the condition into PowerShell manually, I get the correct values if the condition is TRUE or FALSE. But as soon as I use it in the switch, the condition seems to be always TRUE.
What I have so far:
With dsquery I check if a computer belongs to a specific OU.
If a value is returned, which only happens if the query succeeds, I put it into my $SwitchDump variable (Condition TRUE).
From my understanding, if a device is not found in the OU, there is no value that will be passed to my $SwitchDump variable and hence should be $null right?
But it keeps mapping the printer.
Switch ($SwitchDump = dsquery computer $OU_TO_SEARCH_IN|findstr $env:COMPUTERNAME | Out-String)
{
$SwitchDump -ne $null {Add-Printer -ConnectionName \\$PrintServer\$DesiredPrinter}
}
Or am I just barking up the wrong tree?
Any ideas would be greatly appreciated.
$SwitchDump = dsquery computer $OU_TO_SEARCH_IN | findstr $env:COMPUTERNAME | Out-String
Switch ($SwitchDump)
{
{$_ -ne $null} {Add-Printer -ConnectionName \\$PrintServer\$DesiredPrinter}
}
You need to use $_ to represent the variable being tested by the Switch if you want to do anything beyond simple comparisons for values. You also need to make those comparisons a scriptblock by using { }.
You're assigning the dsquery to $SwitchDump... which will [almost] always return true ;-)
You probably want to perform an equality check i.e.
Switch ($SwitchDump -eq dsquery computer $OU...
Also it looks like you have your switch syntax slightly off: https://ss64.com/ps/switch.html
$SwitchDump = dsquery computer $OU_TO_SEARCH_IN|findstr $env:COMPUTERNAME
if (-not $SwitchDump) {
Write-Output "SwitchDump is empty"
}
switch ($SwitchDump) {
$null { Write-Host "SwitchDump = NULL" ; break; }
"value1" { Write-Host "SwitchDump = value1"; break; }
"value2" { Write-Host "SwitchDump = value2"; break; }
"value3" { Write-Host "SwitchDump = value3"; break; }
default { Write-Host "None of the above" ; break; }
}
Very new to coding in general, so I fear I am missing something completely obvious. I want my program to check for a file. If it is there, just continue the code. If it has not arrived, continue cheking for a given amount of time, or untill the file shows up. My loop works on its own, so when i only select the do-part in Powershell ISE, it works. But when i try running it inside the if statement, nothing happens. The loops doesnt begin.
$exists= Test-Path $resultFile
$a = 1
if ($exists -eq "False")
{
do
{
$a++
log "Now `$a is $a "
start-sleep -s ($a)
$exists= Test-Path $resultFile
write-host "exists = $exists"
}
while (($a -le 5) -and ($exists -ne "True"))
}
Another way of doing this is using a while loop:
$VerbosePreference = 'Continue'
$file = 'S:\myFile.txt'
$maxRetries = 5; $retryCount = 0; $completed = $false
while (-not $completed) {
if (Test-Path -LiteralPath $file) {
Write-Verbose "File '$file' found"
$completed = $true
# Do actions with your file here
}
else {
if ($retryCount -ge $maxRetries) {
throw "Failed finding the file within '$maxRetries' retries"
} else {
Write-Verbose "File not found, retrying in 5 seconds."
Start-Sleep '5'
$retryCount++
}
}
}
Some tips:
Try to avoid Write-Host as it kills puppies and the pipeline (Don Jones). Better would be, if it's meant for viewing the script's progress, to use Write-Verbose.
Try to be consistent in spacing. The longer and more complex your scripts become, the more difficult it will be to read and understand them. Especially when others need to help you. For this reason, proper spacing helps all of us.
Try to use Tab completion in the PowerShell ISE. When you type start and press the TAB-key, it will automatically propose the options available. When you select what you want with the arrow down/up and press enter, it will nicely format the CmdLet to Start-Sleep.
The most important tip of all: keep exploring! The more you try and play with PowerShell, the better you'll get at it.
As pointed out in comments, your problem is that you're comparing a boolean value with the string "False":
$exists -eq "False"
In PowerShell, comparison operators evaluate arguments from left-to-right, and the type of the left-hand argument determines the type of comparison being made.
Since the left-hand argument ($exists) has the type [bool] (a boolean value, it can be $true or $false), PowerShell tries to convert the right-hand argument to a [bool] as well.
PowerShell interprets any non-empty string as $true, so the statement:
$exists -eq "False"
is equivalent to
$exists -eq $true
Which is probably not what you intended.
Very new to coding in general, so I fear I am missing something completely obvious. I want my program to check for a file. If it is there, just continue the code. If it has not arrived, continue cheking for a given amount of time, or untill the file shows up. My loop works on its own, so when i only select the do-part in Powershell ISE, it works. But when i try running it inside the if statement, nothing happens. The loops doesnt begin.
$exists= Test-Path $resultFile
$a = 1
if ($exists -eq "False")
{
do
{
$a++
log "Now `$a is $a "
start-sleep -s ($a)
$exists= Test-Path $resultFile
write-host "exists = $exists"
}
while (($a -le 5) -and ($exists -ne "True"))
}
Another way of doing this is using a while loop:
$VerbosePreference = 'Continue'
$file = 'S:\myFile.txt'
$maxRetries = 5; $retryCount = 0; $completed = $false
while (-not $completed) {
if (Test-Path -LiteralPath $file) {
Write-Verbose "File '$file' found"
$completed = $true
# Do actions with your file here
}
else {
if ($retryCount -ge $maxRetries) {
throw "Failed finding the file within '$maxRetries' retries"
} else {
Write-Verbose "File not found, retrying in 5 seconds."
Start-Sleep '5'
$retryCount++
}
}
}
Some tips:
Try to avoid Write-Host as it kills puppies and the pipeline (Don Jones). Better would be, if it's meant for viewing the script's progress, to use Write-Verbose.
Try to be consistent in spacing. The longer and more complex your scripts become, the more difficult it will be to read and understand them. Especially when others need to help you. For this reason, proper spacing helps all of us.
Try to use Tab completion in the PowerShell ISE. When you type start and press the TAB-key, it will automatically propose the options available. When you select what you want with the arrow down/up and press enter, it will nicely format the CmdLet to Start-Sleep.
The most important tip of all: keep exploring! The more you try and play with PowerShell, the better you'll get at it.
As pointed out in comments, your problem is that you're comparing a boolean value with the string "False":
$exists -eq "False"
In PowerShell, comparison operators evaluate arguments from left-to-right, and the type of the left-hand argument determines the type of comparison being made.
Since the left-hand argument ($exists) has the type [bool] (a boolean value, it can be $true or $false), PowerShell tries to convert the right-hand argument to a [bool] as well.
PowerShell interprets any non-empty string as $true, so the statement:
$exists -eq "False"
is equivalent to
$exists -eq $true
Which is probably not what you intended.
I am trying to understand the behavior of the #() array constructor, and I came across this very strange test.
It seems that the value of an empty pipeline is "not quite" the same as $null, even though it is -eq $null
The output of each statement is shown after the ###
$y = 1,2,3,4 | ? { $_ -ge 5 }
$z = $null
if ($y -eq $null) {'y is null'} else {'y NOT null'} ### y is null
if ($z -eq $null) {'z is null'} else {'z NOT null'} ### z is null
$ay = #($y)
$az = #($z)
"ay.length = " + $ay.length ### ay.length = 0
"az.length = " + $az.length ### az.length = 1
$az[0].GetType() ### throws exception because $az[0] is null
So the $az array has length one, and $az[0] is $null.
But the real question is: how is it possible that both $y and $z are both -eq $null, and yet when I construct arrays with #(...) then one array is empty, and the other contains a single $null element?
Expanding on Frode F.'s answer, "nothing" is a mostly magical value in PowerShell - it's called [System.Management.Automation.Internal.AutomationNull]::Value. The following will work similarly:
$y = 1,2,3,4 | ? { $_ -ge 5 }
$y = [System.Management.Automation.Internal.AutomationNull]::Value
PowerShell treats the value AutomationNull.Value like $null in most places, but not everywhere. One notable example is in a pipeline:
$null | % { 'saw $null' }
[System.Management.Automation.Internal.AutomationNull]::Value | % { 'saw AutomationNull.Value' }
This will only print:
saw $null
Note that expressions are themselves pipelines even if you don't have a pipeline character, so the following are roughly equivalent:
#($y)
#($y | Write-Output)
Understanding this, it should be clear that if $y holds the value AutomationNull.Value, nothing is written to the pipeline, and hence the array is empty.
One might ask why $null is written to the pipeline. It's a reasonable question. There are some situations where scripts/cmdlets need to indicate "failed" without using exceptions - so "no result" must be different, $null is the obvious value to use for such situations.
I've never run across a scenario where one needs to know if you have "no value" or $null, but if you did, you could use something like this:
function Test-IsAutomationNull
{
param(
[Parameter(ValueFromPipeline)]
$InputObject)
begin
{
if ($PSBoundParameters.ContainsKey('InputObject'))
{
throw "Test-IsAutomationNull only works with piped input"
}
$isAutomationNull = $true
}
process
{
$isAutomationNull = $false
}
end
{
return $isAutomationNull
}
}
dir nosuchfile* | Test-IsAutomationNull
$null | Test-IsAutomationNull
The reason you're experiencing this behaviour is becuase $null is a value. It's a "nothing value", but it's still a value.
PS P:\> $y = 1,2,3,4 | ? { $_ -ge 5 }
PS P:\> Get-Variable y | fl *
#No value survived the where-test, so y was never saved as a variable, just as a "reference"
Name : y
Description :
Value :
Visibility : Public
Module :
ModuleName :
Options : None
Attributes : {}
PS P:\> $z = $null
PS P:\> Get-Variable z | fl *
#Our $null variable is saved as a variable, with a $null value.
PSPath : Microsoft.PowerShell.Core\Variable::z
PSDrive : Variable
PSProvider : Microsoft.PowerShell.Core\Variable
PSIsContainer : False
Name : z
Description :
Value :
Visibility : Public
Module :
ModuleName :
Options : None
Attributes : {}
The way #() works, is that it guarantees that the result is delievered inside a wrapper(an array). This means that as long as you have one or more objects, it will wrap it inside an array(if it's not already in an array like multiple objects would be).
$y is nothing, it's a reference, but no variable data was stored. So there is nothing to create an array with. $z however, IS a stored variable, with nothing(null-object) as the value. Since this object exists, the array constructor can create an array with that one item.