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cgp
Asked: 2009-06-16 10:42:13 +0800 CST

How to determine how many shells deep I might be?

  • 772

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.

scripting bash

4 Answers

  1. Best Answer
    echo $SHLVL

    From the bash manpage:

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

    • 19

  2. One way is to use pstree:

    $ pstree -h
[...]
├─sshd─┬─sshd───sshd───bash───bash───bash───bash───bash───pstree
│      └─sshd───sshd───bash───bash───bash───bash
[...]
    • 6 
  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
    • 2

  4. Also useful: $BASH_SUBSHELL

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