I suspect this is a " \ " that needs to be doubled.
I tried my alias with ' \\ ' without error message.
impact = !git ls-files -z | xargs -0n1 git blame -w -C | sed -r 's/^[^(]+\\((.*) [0-9]{4}-.*/\\1/' | sed -r 's/ +$//' | sort -f | uniq -c | sort -nr
Vonc
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