Cannot open &STDIN for read at /usr/bin/trizen line 724.

[backdround]

It errors:

su vlad -c bash <<< "trizen --noconfirm -S - <<< fd"
# Cannot open &STDIN for read at /usr/bin/trizen line 724.

It works:

sudo -u vlad bash <<< "trizen --noconfirm -S - <<< fd"

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All work with pacman:

su vlad -c bash <<< "pacman --noconfirm -S - <<< fd"
# and
sudo -u vlad bash <<< "pacman --noconfirm -S - <<< fd"

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I rly don't understand the difference between su and sudo in this context