git-unique-abbrev calc from: How short can Git abbreviate?(Josh Stone)

git-unique-abbrev.sh

#!/bin/bash
# git-unique-abbrev
 
OBJECTS="$(mktemp)"
git rev-list --all --objects | cut -c1-40 | sort >"$OBJECTS"
printf "%d objects\n" $(wc -l <"$OBJECTS")
for abbrev in $(seq 4 40); do
    DUPES="$(mktemp)"
    uniq -D -w $abbrev <"$OBJECTS" >"$DUPES"
    count=$(wc -l <"$DUPES")
    acount=$(uniq -w $abbrev <"$DUPES" | wc -l)
    printf "%2d: %d / %d\n" $abbrev $count $acount
    test $count -eq 0 && cat "$OBJECTS"
    mv "$DUPES" "$OBJECTS"
    test $count -eq 0 && break
done
rm -f "$OBJECTS"