If awk reads all the input, it does not encounter the buffering issue. It can therefore selectively pipe everything after the header to sort via an awk pipe.

df | awk 'NR == 1 { print; next; } /^.dev/ { print | "sort"; }'

I don't have much shm, but I like to report my partitions in sequence, likewise ps output.

Wordy, but maybe worth declaring as a function in .bashrc.

If awk reads all the input, it does not encounter the buffering issue. It can therefore selectively pipe everything after the header to sort via an awk pipe.

df | awk 'NR == 1 { print; next; } /^.dev/ { print | "sort"; }'

I don't have much shm, but I like to report my partitions in sequence, likewise ps output.

Wordy, but maybe worth declaring as a function in .bashrc.

In fact, bash reads lines without buffering, so something like this works too:

df | { read -r Hdr; printf '%s\n' "$Hdr"; grep '^.dev' | sort; }