Get-Content issue with -eq as string

Question

As part of a bigger script I need to verify a file contents before continuing. However, it's not working when I use | Out-String.

Note this needs to work under powershell v2 unfortunately. The file I am looking at contains the data:

{"somedata":5,"hello":[]}

If I remove | Out-String from the command then it tells me the file matches.

But if I add data to the file, then it still tells me the file matches when it doesn't. If I add | Out-String then it tells me the file doesn't match when it does...

$filecheck = Get-Content ("C:\temp\hello.txt") | Out-String
Write-Host $filecheck
if ($filecheck -eq '{"somedata":5,"hello":[]}') {
    Write-Host "file matches"
} else {
    Write-Host "doesn't match"
}

Why do you pipe it into Out-String? Your code works if you remove that. — Palle Due
– Palle Due, Commented Apr 4, 2018 at 10:05
because if there are any additional lines in the file then it still evaluates to true when it's not. — Ian
– Ian, Commented Apr 4, 2018 at 10:45

vonPryz · Accepted Answer · 2018-04-04 10:07:03Z

6

As how to fix the issue, see @tukan's answer. Anyway, for learning purposes, let's explore the root cause, namely using the Out-String cmdlet. It actually adds a newline to the string. Like so,

PS C:\temp> $filecheck = Get-Content ("C:\temp\hello.txt") | Out-String
PS C:\temp> write-host $filecheck
{"somedata":5,"hello":[]}

PS C:\temp>

As the data contains a newline, it isn't equal to the string literal used in the if statement. Thus the comparison fails. Remove the Out-String and it works:

PS C:\temp>$filecheck = Get-Content ("C:\temp\hello.txt")
PS C:\temp> $filecheck
{"somedata":5,"hello":[]}
PS C:\temp> $filecheck -eq '{"somedata":5,"hello":[]}'
True
PS C:\temp>

Earlier you noted that Out-String was needed as otherwise adding data would still make the comparison to fail. Why is that? Let's say the data in file is

{"somedata":5,"hello":[]}
{"moredata":1,"foo":bar}

What now happens is that Get-Content will give you an array of strings. The 2nd line consists of {"moredata":1,"foo":bar} plus a newline. Passing such a construct to the comparison will evaluate just the first element, thus a match.

When you pass an array to Out-String, the result is actually a string with data, newline, data and extra newline:

PS C:\temp> $filecheck|out-string
{"somedata":5,"hello":[]}
{"moredata":1,"foo":bar}

PS C:\temp>

This obviously isn't equal to the string literal used in the if statement.

answered Apr 4, 2018 at 10:07

vonPryz

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2 Comments

Ansgar Wiechers Over a year ago

Good problem analysis. I'm not sure Tukan's answer is a proper solution to the problem, though, since the OP seems to want to check the entire content of a JSON file. $filecheck = (Get-Content "C:\temp\hello.txt" | Out-String).Trim() is probably a better approach.

Ian Over a year ago

yes perfect thank you! the trim will work as I wasn't aware it was adding a new line when using out-string

tukan · Accepted Answer · 2018-04-06 09:13:06Z

1

Edit - the script will exit on first match.
Edit2 - you don't need the Else branch if nothing is found print 'failed' at the end suffice.

What about piping into Foreach-Object like this:

 (Get-Content 'C:\<our_path>\test.txt') |
        Foreach-Object { If ($_ -eq '{"somedata":5,"hello":[]}') {write-host 'matches'; exit}} 
 write-host 'failed'

I have kept your format of -eq, even thou, I would recommend regex for string/text search.

edited Apr 6, 2018 at 9:13

answered Apr 4, 2018 at 9:52

tukan

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4 Comments

henrycarteruk Over a year ago

This gives a line-by-line comparison of the file, not sure if this is what the OP wants?

tukan Over a year ago

@JamesC you are right. Hard to say from the question.

Ian Over a year ago

hi, see what you mean yes this would work but it I only want it to match on the complete file with the first string.

tukan Over a year ago

@Ian you mean exit on first occurrence? If yes, see my edit.

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