xsel for buffer

Install package to save file context into clipboard buffers:

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sudo apt install xsel

To save in the primary (to paste: Shift + Insert, xsel -po):

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cat /etc/hosts | xsel -ip

To save in the secondary (to paste: xsel -so)

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cat /etc/hosts | xsel -is

xsel -x - Exchange the PRIMARY and SECONDARY selections

To save in the clipboard (to paste: Ctrl + V, xsel -bo)

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cat /etc/hosts | xsel -ib

From man:

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Selection options -p, --primary Operate on the PRIMARY selection (default) -s, --secondary Operate on the SECONDARY selection -b, --clipboard Operate on the CLIPBOARD selection