fg 命令的超级技巧：当 Ctrl+Z 拯救你的终端会话

$ ./gradlew build
> Building...

@startuml
skinparam backgroundColor #FEFEFE

actor Développeur as dev
participant "终端" as term
participant "Gradle\n( 进程 )" as gradle

dev -> term : ./gradlew 构建
term -> gradle : 启动构建
gradle -> term : 占用终端\n(无提示)
dev -> term : 想输入一个命令
term --> dev : ❌ 终端被阻塞

note right of dev
开发者在整个构建期间被瘫痪
end note
@enduml

@startuml
skinparam backgroundColor #FEFEFE
autonumber

actor Développeur as dev
participant "终端" as term
participant "Gradle" as gradle
database "状态\n进程" as state

dev -> term : ./gradlew 构建
term -> gradle : 启动构建
gradle -> state : 进行中 (FG)
dev -> term : Ctrl+Z
term -> state : 挂起（作业[1]）
term --> dev : 自由提示 $

dev -> term : git 状态
term --> dev : 工作区干净

dev -> term : fg
term -> state : 重新（FG）
gradle --> dev : 构建成功 ✓

note right of state
进程 Gradle 从未被终止，它精确地恢复到之前停止的位置。
end note
@enduml

# Dans vim, en mode commande :
:shell
$ cat /path/to/other/file.txt
$ exit
# Retour dans vim

# Dans vim, n'importe quel moment :
Ctrl+Z
[1]+  Stoppé    vim README.md

$ cat /path/to/other/file.txt
# ... lire le fichier ...

$ fg
vim README.md
# Retour exact là où on en était, curseur en place

@startuml
skinparam backgroundColor #FEFEFE
autonumber

actor Développeur as dev
participant "vim" as vim
participant "Shell" as shell

dev -> vim : 编辑进行中
dev -> vim : Ctrl+Z
vim -> shell : 挂起 (job [1])
dev -> shell : chat autre_fichier.txt
shell --> dev : 文件内容
dev -> shell : fg
shell -> vim : 重新开始（作业 [1]）
vim --> dev : 光标恰好\n位于相同位置

note right of vim
vim 恢复
int 完整恢复状态：
光标位置，
缓冲区，撤销栈
end note
@enduml

@startuml
skinparam backgroundColor #FEFEFE
skinparam defaultFontName sans-serif
skinparam componentStyle rectangle

actor Développeur as dev
participant "opencode\n(LLM agent)" as agent
participant "Shell" as shell
participant "git" as git

dev -> agent : Session active
agent -> agent : Tour de parole\ndu LLM en cours

note over agent
Ctrl+Z 在代码分析的正中间出现
end note

dev -> agent : 撤销
agent -> shell : Suspendu (job [1])
dev -> git : git diff
git --> dev : 可见的变化
dev -> shell : fg
shell -> agent : 重新开始 (job [1])
agent --> dev : Reprend exactement\nl'analyse en cours

note right of agent
没有上下文丢失
LLM 继续它的回答
正好在它停下的地方
end note
@enduml

$ opencode
# ... session en cours, LLM analyse le code ...
^Z
[1]+  Stoppé    opencode

$ git diff HEAD~1
# vérifier les changements récents

$ fg
opencode
# Le LLM reprend là où il s'était arrêté

$ vim config.yml
^Z
[1]+  Stoppé    vim config.yml

$ ./gradlew test
^Z
[2]+  Stoppé    ./gradlew test

$ htop
^Z
[3]+  Stoppé    htop

$ jobs
[1]   Stoppé    vim config.yml
[2]-  Stoppé    ./gradlew test
[3]+  Stoppé    htop

$ fg %2
./gradlew test
# Le build reprend en avant-plan

$ bg %3
[3] htop &
# htop reprend en arrière-plan

@startuml
skinparam backgroundColor #FEFEFE

rectangle "已暂停的作业" as jobs #LightYellow {
  card "[1] vim config.yml" as j1
  card "[2] ./gradlew 测试" as j2
  card "[3] htop" as j3
}

rectangle "操作" as actions #LightGreen {
  card "fg %2\n→ 前景" as a1
  card "bg %3\n→ 后台" as a2
  card "fg %1\n→ 前景" as a3
}

jobs --> actions : fg/bg + 作业编号
actions --> j2 : 继续
actions --> j3 : 在背景

note bottom of jobs
每个作业保持
其精确状态
在 suspend/resume 之间
end note
@enduml

@startuml
skinparam backgroundColor #FEFEFE
skinparam defaultFontName sans-serif

rectangle "**Ctrl+Z**\nSIGTSTP" as ctrlz #LightYellow {
  card "暂停进程\n(它仍在内存中)\n可使用 fg/bg" as c1
}

rectangle "**Ctrl+C**\nSIGINT" as ctrlc #LightCoral {
  card "结束进程\n(不可恢复)\n丢失所有状态" as c2
}

rectangle "**& **\n(后台)" as ampersand #LightGreen {
  card "直接启动\n在后台\n终端立即空闲" as c3
}

rectangle "**fg**\n(前台)" as fg_ #SkyBlue {
  card "将作业恢复\n挂起的前台\n终端被占用" as c4
}

rectangle "**bg**\n(后台)" as bg_ #Lavender {
  card "恢复作业\n挂起的后台\n终端空闲" as c5
}

ctrlz -right-> fg_ : fg 重新开始
ctrlz -right-> bg_ : bg 用于继续\n在后台
ctrlc -right-> c2 : 没有返回\n进程已被终止

note bottom of ctrlz
进程 **已冻结** 但 **未被杀死**
end note

note bottom of ampersand
替代方案：启动
./gradlew build &
直接在后台
end note
@enduml

@startuml
skinparam backgroundColor #FEFEFE
skinparam defaultFontName sans-serif

title 作业 shell 的完整生命周期
state "不存在" as none
state "前景\n(occupe le terminal)" as foreground #LightCoral
state "已挂起\n(Ctrl+Z / SIGTSTP)" as suspended #LightYellow
state "背景\n(bg ou &)" as background #LightGreen
state "已完成\n(exit code 0)" as done #LightGray

[*] --> none
none --> foreground : 输入一条命令
foreground --> suspended : Ctrl+Z
foreground --> done : 正常结束

suspended --> foreground : fg
suspended --> background : bg
suspended --> done : 杀死 %n

background --> foreground : fg
background --> done : 正常结束\n(en arrière-plan)
background --> suspended : Ctrl+Z\n(si fg puis Ctrl+Z)

done --> [*]

note right of suspended
暂停状态是作业系统的核心枢纽
end note
@enduml

@startuml
skinparam backgroundColor #FEFEFE
skinparam defaultFontName sans-serif
skinparam ArrowColor #444444

title "fg — 这个技巧改变一切"

rectangle "**问题**" as problem #LightCoral {
  card "Terminal 卡住\n由一个进程" as p1
  card "打开 一个新的\n终端 = 笨重的解决方案" as p2
}

rectangle "**解决方案**" as solution #LightGreen {
  card "Ctrl+Z → 挂起" as s1
  card "fg → 恢复" as s2
  card "bg → 后台" as s3
  card "jobs → 查看已挂起的作业" as s4
}

rectangle "**优势**" as advantages #SkyBlue {
  card "无上下文丢失" as a1
  card "无需重启" as a2
  card "只需要一个终端" as a3
}

problem -right-> solution : "此解决方案 native\nUnix 已有40年"
solution -right-> advantages : "结果"

note bottom of advantages
fg 不是一个晦涩的技巧
这是一个基本机制
Unix shell 的
end note
@enduml

@startuml
skinparam backgroundColor #FEFEFE
skinparam defaultFontName sans-serif

rectangle "为什么 fg 被低估了？" as why #LightCoral {
  card "集成开发环境，带多标签终端" as w1
  card "替代 CLI 的图形工具" as w2
  card "tmux/screen\n以另一种方式解决问题" as w3
}

rectangle "为什么 fg 更优？" as superior #LightGreen {
  card "通用：bash,\nzsh, fish, sh..." as s1
  card "无依赖：\n无需安装" as s2
  card "两次按键：\nCtrl+Z 然后 fg" as s3
  card "上下文已保留：\n状态零丢失" as s4
}

why -right-> superior : "简约\n永远胜出"
@enduml

@startuml
skinparam backgroundColor #FEFEFE
skinparam defaultFontName sans-serif

participant "用户" as user
participant "Shell" as shell
participant "进程" as proc

user -> shell : Ctrl+Z
shell -> proc : SIGTSTP (信号 18)
note right of proc : 卡住的进程\n内存中

user -> shell : fg
shell -> proc : SIGCONT (信号 19)
note right of proc : 进程恢复\n 在前台

user -> shell : bg
shell -> proc : SIGCONT (信号 19)
note right of proc : 进程在后台继续

user -> shell : Ctrl+C
shell -> proc : SIGINT (信号 2)
note right of proc : 进程已完成\n状态丢失
@enduml