nco.sh

#!/bin/bash

# nco.sh
#   checkout next/prev commit on current git repository
# Usage:
#   nco [next|prev]
#   use only on detached HEAD branch

if [[ ! -e .git ]]; then
  echo "$PWD is not git repository."
  exit 1
fi

current_branch_name=`git branch | cut -d " " -f 2`
if [[ $current_branch_name != "(HEAD" ]]; then
  echo "current branch is not detached branch"
  exit 1
fi

current=`git log --oneline | awk '{print $1}' | head -n 1`
git checkout main > /dev/null 2>&1
next=`git log --oneline | awk '{print $1}' | grep -B1 $current | head -n1`
prev=`git log --oneline | awk '{print $1}' | grep -A1 $current | tail -n1`

if [[ "$1" = "next" && $next = $current ]]; then
  git checkout $current > /dev/null 2>&1
  echo "this commit is latest commit"
  exit 1
fi

if [[ "$1" = "prev" && $prev = $current ]]; then
  git checkout $current > /dev/null 2>&1
  echo "this commit is first commit"
  exit 1
fi

if [[ "$1" = "next" || "$1" = "" ]]; then
  git checkout $next > /dev/null 2>&1
else
  git checkout $prev > /dev/null 2>&1
fi

git log --oneline | head -n 1