CODEWITHSUNDEEP
powershell
Immortal
Immortal

Reputation: 1200

Comparing String with number in Powershell

I am trying to set an alert if the REMAINING AVAILABLE space of my SQL mdf data FILE is less than 2000 MB. See below:

$SQLInstances = "A","B","C"

$SQLQuery = " USE DB
             SELECT CONVERT(DECIMAL(10, 2), CAST(CAST(10240 - size/128.0 AS NVARCHAR(50)) + size/128.0 - CAST(FILEPROPERTY(name, 'SpaceUsed') AS INT)/128.0 AS NVARCHAR(50))) AS ActualSpaceAvailableMB
             FROM   sys.database_files
             WHERE  name = 'DB'"

$login = "XYZ"
$password = "123" | Convertto-SecureString -AsPlainText -Force
$creds = New-Object System.Management.Automation.Pscredential -Argumentlist $login,$password
$SMTPServer = "10.0.0.0.0.0" # This is your SMTP Server 
$to = "ME@ME.COM"# This is the recipient smtp address 1
$from = "NOREPLY@YOU.COM" # This will be the sender´s address 

foreach ($SQLInstance in $SQLInstances) {
    $output = Invoke-Sqlcmd -ServerInstance $SQLInstance -Database DB -Query  $SQLQuery |
              Select-Object -ExpandProperty ActualSpaceAvailableMB #-QueryTimeout 1200 -Verbose -ErrorAction Stop 4>&1 

    if ($output -lt 2000 ) {
        Send-MailMessage -SmtpServer $SMTPServer -Credential $creds -To $to -From $from -Subject " Alert at  $SQLInstance" -Body "free space is $output MB. Please investigate!!"
    } else {
        Write-Output "Actual size is not less than 2 GB"
    }
}

Now the problem sometimes the alert gives incorrect results i.e. even if the value in the $output variable is greater than 2000 MB an email is still being send. I want it to send an email ONLY if the value in the $output is less than 2000. Any ideas?

Upvotes: 1

Views: 3748

Answers (2)

js2010
js2010

Reputation: 27606

You can do it the other way so $output gets cast to integer, instead of 2000 getting cast to string.

if ($output -and 2000 -ge $output) {

EDIT: added a null check

For example, this turns out to be true when they're both strings, which is not what you want.

 '90' -gt 100

Upvotes: 0

Ansgar Wiechers
Ansgar Wiechers

Reputation: 200503

Comparisons in PowerShell have a tendency to yield unexpected results, because PowerShell tries to adjust the type of the second operand to match the type of the first operand. Thus if your first operand is a string the comparison will be a string comparison, not a numeric comparison.

Demonstration:

PS C:\> $s = '20'
PS C:\> $s -gt 10    # ⇔ "20" -gt "10"
True
PS C:\> $s -gt 100   # ⇔ "20" -gt "100"
True
PS C:\> $s -gt 3     # ⇔ "20" -gt "3"
False

To mitigate this cast the first operand to a numeric type:

PS C:\> [int]$s -gt 100
False
PS C:\> [int]$s -gt 3
True

Upvotes: 7

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