How to determine how many shells deep I might be?

Question

I'm wondering whether I've called the shell recursively, is there an easy way to find out? Is any solution specific to the shell? I'm using bash.

Answer 1

echo $SHLVL

From the bash manpage:

SHLVL Incremented by one each time an instance of bash is started.

Answer 2

One way is to use pstree:

$ pstree -h
[...]
├─sshd─┬─sshd───sshd───bash───bash───bash───bash───bash───pstree
│      └─sshd───sshd───bash───bash───bash───bash
[...]

Answer 3

echo $SHLVL

This will catch if you do something like:

[sharpestmarble@sandbox ~]$ bash

Although that won't catch something like if you SSH into localhost.

[sharpestmarble@sandbox ~]$ ssh localhost

Answer 4

Also useful: $BASH_SUBSHELL

$ echo $SHLVL
1
$ (echo $SHLVL)
1
$ echo $BASH_SUBSHELL
0
$ (echo $BASH_SUBSHELL)
1
$ ( (echo $BASH_SUBSHELL) )
2