PowerShell - continue if string is not contained in file (detect when a cmdlet returns nothing)

Question

I am searching for a string ($Loan_Id) in a file ($File_LoanData). I am able to find it, but should the string not be found, I need the script to continue. That does not seem to be working. Here is the problem line -- if ($Note_Line -eq $false) {Continue}

$Fie_LCExtract = "c:\temp\Fie_LCExtract.txt"
$File_LoanData = "c:\temp\File_LoanData.txt"
$File_LoanDataToday = "c:\temp\File_LoanDataToday.txt"
$r = [IO.File]::OpenText($Fie_LCExtract)
while ($r.Peek() -ge 0) 
    {
     $Note = $r.ReadLine()
     $Loan_Id = ($Note -split ';')[0].trim()
     $Loan_Id = $Loan_Id -as [int]
     if (($Loan_Id -is [int])  -eq $false) {Continue}
     $Note_Line = Select-String -Path $File_LoanData -Pattern $Loan_Id
     if ($Note_Line -eq $false)   {Continue}
     $Note_Line =  ($Note_Line -split ':')[3].trim()
     $Note_Line  >> $File_LoanDataToday
   }

mklement0 · Accepted Answer · 2018-03-11 06:40:04Z

2

Don't compare to $False, use the return value directly as if it were a Boolean:

if (-not $Note_Line) { Continue }

Alternatively, compare to $null:

if ($null -eq $Note_Line) { Continue }

Or use the .Count property:

if ($Note_Line.Count -eq 0) { Continue }

Select-String returns a "null collection" ("nothing") when it finds no matches and this special value ([System.Management.Automation.Internal.AutomationNull]::Value) is "falsy" in a Boolean context; also, it is considered equal to $null and its .Count property is always 0.

However, despite a null collection implicitly being considered $False, comparing it explicitly to $False does not yield $True:

The null collection is treated like $null in an expression context, and the only value that $null equals (-eq) is $null itself^[1].

$null -eq $False # !! $False
$null -eq $null  # $True

Using a null collection / $null implicitly as a Boolean is equivalent to casting it to [bool], so we can see that it is "falsy":

[bool] $null  # $False

^{[1] This applies to using $null as the LHS of -eq. As the RHS,
if the LHS is array-valued, it act as a filter and returns the sub-array of elements containing $null.

For instance, $null, 1, $null -eq $null returns a 2-element array of $null values.}

edited Mar 11, 2018 at 6:40

answered Mar 11, 2018 at 6:05

mklement0

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1 Comment

hdsouza Over a year ago

Works great. Thanks a lot.

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