$SHELL does not reflect current shell

student04 · 06-10-2008, 08:08 AM

On both Solaris 8 and 10 I have the following:

Code:

user@computer>uname -a
SunOS computer 5.8 Generic_117350-39 sun4u sparc SUNW,Ultra-60
user@computer>echo $SHELL
/bin/csh
user@computer>which bash
/usr/bin/bash
user@computer>/usr/bin/bash
bash-2.03$ echo $SHELL
/bin/csh
bash-2.03$
bash-2.03$ ps -ef | grep user
user 22458 21665  0 09:01:44 pts/8    0:00 /usr/bin/bash
user 22475 22458  0 09:03:18 pts/8    0:00 grep user
user 21665 21663  0 08:29:38 pts/8    0:00 -csh
bash-2.03$

Why does this variable not update? How am I supposed to determine which shell I am running without visually seeing "bash" in the prompt (for all I know the prompt could be modified in some configuration file to look like that of a csh shell, using the "%" character).

-AM

colucix · 06-10-2008, 09:30 AM

According to the BASH manual page

Code:

SHELL  The full pathname to the shell is kept in this environment variable. If it is not set when the
       shell starts, bash assigns to it the full pathname of the current user’s login shell.

I don't know how to force the shell to set the SHELL variable upon invocation, but a unique method to determine the current shell is

Code:

echo $0

if the current shell is the login shell you will get something like -csh (that is if the first character of $0 is -, it is a login shell), otherwise you will get the full pathname of the current shell.

student04 · 06-10-2008, 11:27 AM

Ah, that's interesting. See, I've relied on the value set in this variable to determine what shell I was running. Now that it's not consistent, I'm confused.

When I run the echo command from within my login shell I get the following:

Code:

user@computer>echo $0
No file for $0

But, invoking bash beforehand it tells me what I have correctly:

Code:

user@computer>/usr/bin/bash
bash-2.03$ echo $0
/usr/bin/bash
bash-2.03$

So even though this variable is incorrect I can assume that when I run 'bash' I am in the BASH shell? A silly question, but having made this assumption in the past that's what I looked at... Oh and I am using telnet not ssh if that makes a difference (for reasons I have no authority over).

Thanks,
AM

colucix · 06-10-2008, 11:59 AM

Yes, sorry. The C-shell is an exception to the echo $0 method. A more portable way is

Code:

ps -p $$ -o comm=

this prints out the command associated to the process ID of the current shell. As you probably know, the special variable $$ holds the process ID of the script in which it appears. For interactive shells it is the process ID of the shell itself. Also note that the equal sign at the end of the output format specification is meant to suppress the header of the ps output. I tested on Solaris 5.8 and it works.

student04 · 06-10-2008, 01:22 PM

Thanks. I learn new things everyday.

-AM