Linux equivalent of $SHLVL or $SH_LEVEL

jisner · 11-04-2006, 05:56 PM

This is my first post. I have some shell scripts that I'm bringing over from Solaris to Linux (Ubuntu). Several of these scripts mention the shell variable $SH_LEVEL and $SHLVL. Both variables are defined in Linux, but both always return 1, rather than indicating the actual shell depth. For example:

echo $SHLVL
1
bash
echo $SHLVL
1

etc.

What is the correct way to determine the shell depth, or is this concept missing in Linux?

matthewg42 · 11-04-2006, 08:00 PM

That is very strange - it works as expected for me, and I only see SHLVL:

Code:

matthew@chubby:~$ set |grep -e LVL -e LEV
SHLVL=1
matthew@chubby:~$ bash
matthew@chubby:~$ set |grep -e LVL -e LEV
SHLVL=2

What version of bash / Ubuntu are you using? I'm on edgy running the 386 kernel with bash as follows:

Code:

matthew@chubby:~$ bash --version
GNU bash, version 3.1.17(1)-release (i486-pc-linux-gnu)
Copyright (C) 2005 Free Software Foundation, Inc.

jisner · 11-05-2006, 08:53 AM

Ah, thanks. I have to admit that I lied in my original post. I'm actually using ksh, but I thought it didn't matter when I typed the example. With ksh, these variables are always 1. So I guess the problem is with ksh. Versions: ksh (93q+93r-1)on Ubuntu (6.06).

soggycornflake · 11-05-2006, 09:25 AM

Works fine in zsh too. I just tried ksh (93) with SHLVL currently at 2 and it's still 2, so I guess ksh doesn't use it at all.

matthewg42 · 11-05-2006, 09:29 AM

Quote:

Originally Posted by jisner

Ah, thanks. I have to admit that I lied in my original post. I'm actually using ksh, but I thought it didn't matter when I typed the example. With ksh, these variables are always 1. So I guess the problem is with ksh. Versions: ksh (93q+93r-1)on Ubuntu (6.06).

I don't think ksh supports this feature. There's no mention of it in the manual page, and looking though the built-in special variables names, I couldn't fund anything which looks like it does the same thing.

jisner · 11-06-2006, 08:17 AM

Quote:

Originally Posted by matthewg42

I don't think ksh supports this feature. There's no mention of it in the manual page, and looking though the built-in special variables names, I couldn't fund anything which looks like it does the same thing.

It worked on Solaris, so I think this must have something to do with Linux, or the Linux version of ksh. Oh well, it's not critical. Thanks for your comments!

matthewg42 · 11-06-2006, 09:01 AM

Perhaps the Solaris ksh is newer, or on that system it has been fudged to use SHLVL.

Here's how to fudge it. In your .profile, add the line:

Code:

export ENV="$HOME/.ksh_shlvl"

Then create the file $HOME/.ksh_shlvl and put this in it:

Code:

if [ "$SHLVL" = "" ]; then
  SHLVL=1
else
  let SHLVL+=1
fi

If you want it system-wide, you can put the ENV in the /etc/profile of course, and have the location of .ksh_shlvl somewhere else, e.g. /etc/ksh_shlvl.

Caveats:

1. The first shell you open has to be a login shell. All subsequent shells will inhert the ENV value as long as you exported it in the first shell. Therefore this might not work in scripts unless you explicitly set the ENV value, but I think all shells you start after re-logging into X (or the console) should have it. I'm assuming you use ksh as your interactive shell here. Be careful about cron jobs - you don't get the /etc/profile or the local .profile executed in cron shells.

2. You can't use your ENV variable for anything else. If you need it for something else, you;ll have to handle the SHLVL thing yourself.

3. Forgetting to copy that weird .ksh_shlvl file to a new system may break your scripts. Fudges like this invariably lead to annoying problems.

4. If someone annoyingly sets SHLVL to a non-integer, you're going to get annoying errors.