Very probably not the fastest possible solution, but it does what I need:
#!/bin/bash REV=$1 if [[ -z "$REV" ]]; then echo "Usage: git-get-child []" exit fi HASH=$(git rev-parse $REV) NUM=$2 if [[ -z "$NUM" ]]; then NUM=1 fi git rev-list --all --parents | grep " $HASH" | sed -n "${NUM}s/\([^ ]*\) .*$/\\1/p"
The git rev-list --all --parents
does exactly what I need: it iterates over all reachable commits, and prints the following line for each:
SHA1_commit SHA1_parent1 SHA1_parent2
etc.
The space in the grep expression ensures that only those lines are found where the SHA1 in question is a parent. Then we get the nth line for the nth child and get the child’s SHA1.