Why does a multi-line file not compare equal to itself?

Question

When I use gc (get-content) on the same file twice, and compare the strings using -eq, why does it compare unequal?

$f = "C:\temp\test.txt"
echo Hello > $f
echo World >>$f # works if I uncomment this line

gc $f

# get the contents of the file twice and compare it to itself.
if ((gc $f) -eq (gc $f)) {
    Write-Host "Hooray! The file is the same as itself."
} else {
    Write-Host "Boo."
}

Prints Boo., unless I comment out the 3rd line - the problem only seems to occur with multiline files.

(obviously in reality I wouldn't compare the file to itself, in real life I'm comparing two files that might have identical content).

I'm running powershell 2.0.

Answer 1

That will work if the file has only one line, but will fail if there are multiple lines because of the way -eq works as an array operator. For it to work as expected you need to compare both as scalar (single item) objects. One way to do this is to add the -Raw switch to Get-Content if you've got V3 or better.

if ((gc $f -raw) -eq (gc $f -raw))

That will read the entire file as a single, multi-line string.

To accomplish the same in V2:

if ([io.file]::ReadAllText($f)) -eq ([io.file]::ReadAllText($f))

or

if ([string](gc $f) -eq [string](gc $f))