git-obj-walk.sh

git-obj-walk.sh

#!/bin/bash

set +o pipefail

if (( $# != 1 )); then
    echo "usage: $0 <ref>" >&2
    exit 1
fi

if ! command -v git >/dev/null 2>&1; then
    echo "error: git executable not found" >&2
    exit 1
fi

ref="$1"
obj=$(git rev-parse "$ref" 2>/dev/null)
if (( $? != 0 )); then
    echo "error: unknown revision or not a git repository" >&2
    exit 1
fi

while true; do
    readarray -d ' ' -t tokens <<< "$(git cat-file -p "$obj" 2>/dev/null | head -1)"
    if (( $? != 0 || ${#tokens[@]} < 2 )); then
        echo "error: unable to determine details of object: $obj" >&2
        exit 1
    fi
    
    type=$(git cat-file -t "$obj" 2>/dev/null)
    if (( $? != 0 )); then
        echo "error: unable to obtain content of object: $obj" >&2 
        exit 1
    fi

    node="${node:+ -> }[ $type:${obj:0:6} ]"
    echo -n "$node"
    
    case "${tokens[0]}" in
        object|tree)
            obj="$(tr -d '\n' <<< "${tokens[1]}")"
            ;;
        *)
            echo
            break
            ;;
    esac

done

Example:

$ ./git-obj-walk.sh v1.0.0
[ tag:45de3d ] -> [ commit:45be62 ] -> [ tree:52a266 ]