The following code
"a,b,c
1,1,1
2,,2
3,3,3" > test.csv
import-csv test.csv | select b | % {
Write-Host "$_ $([string]::IsNullOrEmpty($_))"
}
returns
@{b=1} False
@{b=} False
@{b=3} False
However, I expected the second line return True. I tried $_ -eq $null -or $_ -eq '' and none if them work?
The issue is that inside of the % { } block $_ does not contain the value of column b but rather an object with a b property. When you run [string]::IsNullOrEmpty($_) you are testing if this object is null or an empty string, neither of which is true.
To illustrate what's happening, compare the results of...
Import-Csv .\test.csv | Get-Member
...with the results of...
Import-Csv .\test.csv | select b | Get-Member
...with the results of...
Import-Csv .\test.csv | select -ExpandProperty b | Get-Member
One solution is to test if the b property of the object produced by select (rather than the object itself) is null or empty:
import-csv test.csv | select b | % {
Write-Host "$_ $([string]::IsNullOrEmpty($_.b))"
}
Another solution is to pass only the value of column b to the % { } block:
import-csv test.csv | select -ExpandProperty b | % {
Write-Host "$_ $([string]::IsNullOrEmpty($_))"
}
I found the following code works.
import-csv test.csv | select b | % {
Write-Host "$_ $($_.b -eq '')"
}
Is there any other solution?
In your example in the question there is still an object present with an empty b parameter. Consider the following which shows why you got the result you did.
PS C:\Users\matt> @{} -eq $null
False
The rest of this would be to expand the property much like in Bacon's answer
