reflog:记录什么、什么时候过期

  $ cat .git/logs/HEAD | sed -E 's/^0{40}/<全 0>/; s/[0-9a-f]{40}/<hash>/g; s/ [0-9]{10} /  <时间戳> /'
  <全 0> <hash> Alice <alice@example.com>  <时间戳> +0800	commit (initial): 提交 1
  <hash> <hash> Alice <alice@example.com>  <时间戳> +0800	commit: 提交 2
  <hash> <hash> Alice <alice@example.com>  <时间戳> +0800	checkout: moving from main to dev
  <hash> <hash> Alice <alice@example.com>  <时间戳> +0800	checkout: moving from dev to main
  <hash> <hash> Alice <alice@example.com>  <时间戳> +0800	reset: moving to HEAD~1

  $ ls .git/logs .git/logs/refs/heads
  .git/logs:
  HEAD
  refs
  
  .git/logs/refs/heads:
  dev
  main
  $ git reflog show main --format='%gd: %gs'
  main@{0}: reset: moving to HEAD~1
  main@{1}: commit: 提交 2
  main@{2}: commit (initial): 提交 1
  $ for i in 0 1 2 3; do printf 'HEAD@{%s} → ' $i; git log -1 --format=%s HEAD@{$i}; done
  HEAD@{0} → 提交 1
  HEAD@{1} → 提交 2
  HEAD@{2} → 提交 2
  HEAD@{3} → 提交 2
  $ { git log -1 --format=%s 'main@{5.minutes.ago}'; git log -1 --format=%s 'main@{1.hour.ago}'; } 2>&1 | sed -E 's/goes back to .*/goes back to <该 reflog 第一条记录的时间>/'
  warning: log for 'main' only goes back to <该 reflog 第一条记录的时间>
  提交 1
  warning: log for 'main' only goes back to <该 reflog 第一条记录的时间>
  提交 1

  $ git reflog --format='%gd: %gs' | cut -c1-70
  HEAD@{0}: rebase (finish): returning to refs/heads/main
  HEAD@{1}: rebase (pick): 主线提交
  HEAD@{2}: rebase (start): checkout side
  HEAD@{3}: commit (amend): 改了说明
  HEAD@{4}: merge side: Merge made by the 'ort' strategy.
  HEAD@{5}: commit: 主线提交
  HEAD@{6}: checkout: moving from side to main
  HEAD@{7}: commit: 侧枝提交
  HEAD@{8}: checkout: moving from main to side
  HEAD@{9}: commit (initial): 提交 1

  $ ls .git/logs/refs; ls .git/logs/refs/heads; ls .git/logs/refs/tags 2>&1 | head -1; git config core.logAllRefUpdates || echo "(未设置)"
  heads
  main
  side
  ls: .git/logs/refs/tags: No such file or directory
  true
  $ git -c core.logAllRefUpdates=always tag v2; ls .git/logs/refs/tags
  v2
  $ rm -rf l25bare.git && git init -q --bare l25bare.git && cd l25bare.git && git config core.logAllRefUpdates || echo "(裸仓库:未设置)"; H=$(git hash-object -w -t tree /dev/null); C=$(GIT_AUTHOR_NAME=a GIT_AUTHOR_EMAIL=a@e GIT_COMMITTER_NAME=a GIT_COMMITTER_EMAIL=a@e git commit-tree $H -m x); git update-ref refs/heads/main $C; ls logs 2>&1 | head -2; echo "(以上是裸仓库 update-ref 之后 logs 目录的内容)"
  (裸仓库:未设置)
  ls: logs: No such file or directory
  (以上是裸仓库 update-ref 之后 logs 目录的内容)

  expire 之前:
  $ git reflog --format='%gd  %gs' --date=relative | sed -E 's/ago\}/ago}/'
  HEAD@{5 days ago}  commit: C-5天前
  HEAD@{10 days ago}  checkout: moving from tmp to main
  HEAD@{3 weeks ago}  commit: U2-20天前
  HEAD@{6 weeks ago}  commit: U1-40天前
  HEAD@{3 months ago}  checkout: moving from main to tmp
  HEAD@{3 months ago}  commit: B-100天前
  HEAD@{4 months ago}  commit (initial): A-120天前
  $ git reflog expire --all; echo "(已执行 git reflog expire --all,使用默认过期时间)"
  (已执行 git reflog expire --all,使用默认过期时间)
  expire 之后:
  $ git reflog --format='%gd  %gs' --date=relative | sed -E 's/ago\}/ago}/'
  HEAD@{5 days ago}  commit: C-5天前
  HEAD@{10 days ago}  checkout: moving from tmp to main
  HEAD@{3 weeks ago}  commit: U2-20天前

  $ git reset -q --hard HEAD~2; git log --format=%s; git reflog --format='%gd: %gs' | head -4
  提交 1
  HEAD@{0}: reset: moving to HEAD~2
  HEAD@{1}: commit: 提交 3
  HEAD@{2}: commit: 提交 2
  HEAD@{3}: commit (initial): 提交 1
  $ git reset -q --hard HEAD@{1}; git log --format=%s
  提交 3
  提交 2
  提交 1
  $ git reflog expire --expire=now --all; git reflog | wc -l; git reset --hard HEAD@{1} 2>&1 | head -2
         0
  fatal: log for HEAD is empty