Determining user's current shell

[Deepak Extross]

I need to check if the user's current shell is csh.
$shell isn't foolproof, and I'm sure there must be a more elegant alternative to running a csh-specific command and checking $?.
Any ideas?

[Steven Sim Kok Leong]

Hi,

login shell can be extracted from /etc/passwd. For current shell, I prefer the easier way of checking the last access timestamp of the .profile, .cshrc, .bashrc, .dtprofile etc.

1) Check user profile access time, eg. for csh,

$ ls -lu .cshrc
- -rw-r--r-- 1 user1 users 814 Feb 18 20:02 .cshrc
$ csh
sys 21: ls -lu .cshrc
- -rw-r--r-- 1 user1 users 814 Feb 19 13:50 .cshrc

2) Use syntax testing:

For sh/ksh/bash,
# export a=1

For csh, tcsh,
# echo >/dev/null 2>&1
Ambiguous output redirect.
# echo $?
Variable syntax.

Hope this helps. Regards.

Steven Sim Kok Leong

[Steven Sim Kok Leong]

Hi,

One issue with using the last access timestamps on .cshrc user profile is that the user can skip its execution (if he wants to) by executing:

# csh -f

Thus, a syntax check though more inconvenient is still more reliable:

For sh/ksh/bash:
# setenv
sh: setenv: not found.

For csh:
sys 21: setenv
setenv: Too few arguments.

Hope this helps. Regards.

Steven Sim Kok Leong

[Steven Sim Kok Leong]

Hi,

The $SHELL variable only works for the login shell which can be extracted from /etc/passwd:

$ echo $SHELL
/usr/bin/sh
$ csh
sys 21: echo $SHELL
/usr/bin/sh

If you wish to prevent $SHELL from being tampered, you can add this in your /etc/profile between the traps:

readonly SHELL

Hope this helps. Regards.

Steven Sim Kok Leong

[SHABU KHAN]

hi,

how about:

env | egrep 'csh|ksh'

-Shabu

[Deepak Extross]

Hi Shabu,
I'm looking for current shell, not default shell.
To make matters worse, the user can have multiple telnet sessions open, each running a different shell.
Syntax-testing as suggested by Steven will definitely work, but I was looking for a more elegant solution.

[Steven Sim Kok Leong]

Hi Deepak,

For different windows, if the prompt is different for each profile, .cshrc etc then the prompt can be used to identify the shell a user is current running, ie.

sh/ksh/bash:

$ ksh
$
$

csh/tcsh:

$ csh
sys 21:
sys 21:

In .cshrc,

set prompt = "$system \!: "

Hope this helps. Regards.

[Steven Sim Kok Leong]

Hi,

I think I have found the elegant solution you wanted:

Execute this:

# ps -fp `echo $$`

$ ksh
$ ps -fp `echo $$`
UID PID PPID C STIME TTY TIME COMMAND
user1 16088 16079 0 15:01:49 pts/0 0:00 ksh

$ csh
sys 21: ps -fp `echo $$`
UID PID PPID C STIME TTY TIME COMMAND
user1 16334 16088 0 15:06:28 pts/0 0:00 csh

sys 22: sh
$ ps -fp `echo $$`
UID PID PPID C STIME TTY TIME COMMAND
user1 16345 16334 0 15:06:40 pts/0 0:00 sh

You can thus incorporate this in your script eg:

shell_used=`ps -fp `echo $$`|tail -1|awk '{print $8}'`

Hope this helps. Regards.

Steven Sim Kok Leong

[Steven Sim Kok Leong · Accepted solution]

Hi,

The echo is redundant.

Instead of ps -fp `echo $$`, ps -fp $$ alone is sufficient.

# ps -fp $$|tail -1|awk '{print $8}'

shell_used=`ps -fp $$|tail -1|awk '{print $8}'`

Hope this helps. Regards.

Steven Sim Kok Leong

[Deepak Extross]

Thanks, Steven!
That deserves a bunny :-)

[Robin Wakefield]

Hi Deepak,

Probably best to just use "ps -p $$", then you don't have to worry about the timestamp being 1 or 2 fields long:

shell_used=`ps -p $$ | awk /:/'{print $4}'`

Rgds, Robin.

[Steve Steel]

Hi

If you start from another shell or not.

shell in lowercase is set to /usr/bin/csh if you are using csh.

Otherwise if your shell has been open for a while there can be 9 parameters with the 9th as shell name

This works



#!/sbin/sh
MYSHELL=$(ps -fp $$|tail -1|sed -e 's/^.* //' -e 's/-//')

run as . showshell

Then MYSHELL is correct or adjust the previous
entry.

Steve Steel