Delete duplicate string with PowerShell

Question:

I have got text file:

1 2 4 5 6 7
1 3 5 6 7 8
1 2 3 4 5 6
1 2 4 5 6 7

1 2 4 5 6 7

1 3 5 6 7 8

1 2 3 4 5 6

1 2 4 5 6 7

Here first and last line are simmilar. I have a lot of files that have double lines. I need to delete all dublicate.

All these seem really complicated. It is as simple as:

gc $filename | sort | get-unique > $output

1 2	gc $filename \| sort \| get-unique > $output

Using actual file names instead of variables:

gc test.txt| sort | get-unique > unique.txt

1 2	gc test.txt\| sort \| get-unique > unique.txt