When using a *nix shell (usually bash), I often spawn a sub-shell with which I can take care of a small task (usually in another directory), then exit out of to resume the session of the parent shell.
在使用*nix shell(通常是bash)时，我经常生成一个子shell，我可以用它来处理一个小任务(通常在另一个目录中)，然后退出以恢复父shell的会话。
Once in a while, I'll lose track of whether I'm running a nested shell, or in my top-level shell, and I'll accidentally spawn an additional sub-shell or exit out of the top-level shell by mistake.
偶尔，我将会忘记我是在运行一个嵌套的shell，还是在我的*shell中，我将会错误地产生一个额外的子shell或者从顶层shell中退出。
Is there a simple way to determine whether I'm running in a nested shell? Or am I going about my problem (by spawning sub-shells) in a completely wrong way?
是否有一种简单的方法来确定我是否在嵌套shell中运行?还是我在用完全错误的方式处理我的问题(通过生成子壳层)?
7 个解决方案
#1
62
The $SHLVL variable tracks your shell nesting level:
$SHLVL变量跟踪您的shell嵌套级别:
$ echo $SHLVL
1
$ bash
$ echo $SHLVL
2
$ exit
$ echo $SHLVL
1
As an alternative to spawning sub-shells you could push and pop directories from the stack and stay in the same shell:
作为生成子shell的替代方法，您可以从堆栈中推出和弹出目录，并保持在相同的shell中:
[root@localhost /old/dir]# pushd /new/dir
/new/dir /old/dir
[root@localhost /new/dir]# popd
/old/dir
[root@localhost /old/dir]#
#2
21
Here is a simplified version of part of my prompt:
以下是我的部分提示的简化版本:
PS1='$(((SHLVL>1))&&echo $SHLVL)\$ '
If I'm not in a subshell, it doesn't add anything extra, but it shows the depth if I'm in any level of subshell.
如果我不在子层中，它不会添加任何额外的东西，但是它显示了在任何子层中的深度。
#3
11
Look at $0: if it starts with a minus -, you're in the login shell.
看看$0:如果它以-开头，你就在登录shell中。
#4
6
pstree -s $$ is quite useful to see your depth.
pstree -s $$ $对你的深度非常有用。
#5
0
ptree $$ will also show you how many levels deep you are
ptree $$ $也会显示你的深度
#6
0
The environment variable $SHLVL contains the shell "depth".
环境变量$SHLVL包含shell“depth”。
echo $SHLVL
The shell depth can also be determined using pstree (version 23 and above):
外壳深度也可以使用pstree(版本23及以上):
pstree -s $$ | grep sh- -o | wc -l
I've found the second way to be more robust than the first whose value was reset when using sudo or became unreliable with env -i.
我发现第二种方法比第一个更健壮，当使用sudo时，它的值被重置，或者使用env -i变得不可靠。
None of them can correctly deal with su.
他们中没有一个人能正确地处理su。
The information can be made available in your prompt:
有关资料可于下列网址查阅:
PS1='\u@\h/${SHLVL} \w \$ '
PS1='\u@\h/$(pstree -s $$ | grep sh- -o | tail +2 | wc -l) \w \$ '
The | tail +2 is there to remove one line from the grep output. Since we are using a pipeline inside a "$(...)" command substitution, the shell needs to invoke a sub-shell, so pstree report it and grep detects one more sh- level.
| tail +2用于从grep输出中删除一行。由于我们在“$(…)”命令替换中使用管道，因此shell需要调用一个子shell，因此pstree报告它，grep检测到另一个sh- level。
In debian-based distributions, pstree is part of the package psmisc. It might not be installed by default on non-desktop distributions.
在基于debianbased的发行版中，pstree是psmisc包的一部分。默认情况下，它可能不会安装在非桌面发行版上。
#7
-1
If you running inside sub-shell following code will yield 2:
如果您在子shell中运行以下代码，将产生2:
ps | fgrep bash | wc -l
Otherwise, it will yield 1.
否则，它会产生1。
EDIT Ok, it's not so robust approach as was pointed out in comments :)
Another thing to try is
编辑Ok，它不像注释中指出的那样健壮
ps -ef | awk '{print $2, " ", $8;}' | fgrep $PPID
will yield 'bash' if you in sub-shell.
如果在子shell中，将产生“bash”。
#1
62
The $SHLVL variable tracks your shell nesting level:
$SHLVL变量跟踪您的shell嵌套级别:
$ echo $SHLVL
1
$ bash
$ echo $SHLVL
2
$ exit
$ echo $SHLVL
1
As an alternative to spawning sub-shells you could push and pop directories from the stack and stay in the same shell:
作为生成子shell的替代方法，您可以从堆栈中推出和弹出目录，并保持在相同的shell中:
[root@localhost /old/dir]# pushd /new/dir
/new/dir /old/dir
[root@localhost /new/dir]# popd
/old/dir
[root@localhost /old/dir]#
#2
21
Here is a simplified version of part of my prompt:
以下是我的部分提示的简化版本:
PS1='$(((SHLVL>1))&&echo $SHLVL)\$ '
If I'm not in a subshell, it doesn't add anything extra, but it shows the depth if I'm in any level of subshell.
如果我不在子层中，它不会添加任何额外的东西，但是它显示了在任何子层中的深度。
#3
11
Look at $0: if it starts with a minus -, you're in the login shell.
看看$0:如果它以-开头，你就在登录shell中。
#4
6
pstree -s $$ is quite useful to see your depth.
pstree -s $$ $对你的深度非常有用。
#5
0
ptree $$ will also show you how many levels deep you are
ptree $$ $也会显示你的深度
#6
0
The environment variable $SHLVL contains the shell "depth".
环境变量$SHLVL包含shell“depth”。
echo $SHLVL
The shell depth can also be determined using pstree (version 23 and above):
外壳深度也可以使用pstree(版本23及以上):
pstree -s $$ | grep sh- -o | wc -l
I've found the second way to be more robust than the first whose value was reset when using sudo or became unreliable with env -i.
我发现第二种方法比第一个更健壮，当使用sudo时，它的值被重置，或者使用env -i变得不可靠。
None of them can correctly deal with su.
他们中没有一个人能正确地处理su。
The information can be made available in your prompt:
有关资料可于下列网址查阅:
PS1='\u@\h/${SHLVL} \w \$ '
PS1='\u@\h/$(pstree -s $$ | grep sh- -o | tail +2 | wc -l) \w \$ '
The | tail +2 is there to remove one line from the grep output. Since we are using a pipeline inside a "$(...)" command substitution, the shell needs to invoke a sub-shell, so pstree report it and grep detects one more sh- level.
| tail +2用于从grep输出中删除一行。由于我们在“$(…)”命令替换中使用管道，因此shell需要调用一个子shell，因此pstree报告它，grep检测到另一个sh- level。
In debian-based distributions, pstree is part of the package psmisc. It might not be installed by default on non-desktop distributions.
在基于debianbased的发行版中，pstree是psmisc包的一部分。默认情况下，它可能不会安装在非桌面发行版上。
#7
-1
If you running inside sub-shell following code will yield 2:
如果您在子shell中运行以下代码，将产生2:
ps | fgrep bash | wc -l
Otherwise, it will yield 1.
否则，它会产生1。
EDIT Ok, it's not so robust approach as was pointed out in comments :)
Another thing to try is
编辑Ok，它不像注释中指出的那样健壮
ps -ef | awk '{print $2, " ", $8;}' | fgrep $PPID
will yield 'bash' if you in sub-shell.
如果在子shell中，将产生“bash”。