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.

score 19 · Accepted Answer · answered Jun 15 '09 at 18:46

19

echo $SHLVL

From the bash manpage:

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

answered Jun 15 '09 at 18:46

brian-brazil

Ah, there it is! – cgp Jun 15 '09 at 18:47
2

So I guess checking the parent process ID recursively would be a waste of time, eh? – sangretu Jun 15 '09 at 18:50
1

Checking the parent process does have the advantage that it'll work for any shell. – brian-brazil Jun 15 '09 at 18:52

score 6 · Answer 2 · answered Jun 15 '09 at 18:50

One way is to use pstree:

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

score 2 · Answer 3 · answered Jun 15 '09 at 18:48

2

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

answered Jun 15 '09 at 18:48

Kevin M

score 1 · Answer 4 · answered Jun 16 '09 at 19:40

1

Also useful: $BASH_SUBSHELL

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

answered Jun 16 '09 at 19:40

Dennis Williamson

4 Answers4