What Shell Are You Using Currently?

devUnix · 01-04-2011, 09:17 AM

Hi,

Is there anyway to find out what shell we are currently using?

For example, I logged in and issued the following command to check my current shell:

Code:

%echo $SHELL
/bin/sh

then I changed to bash by executing the following command and checked again as to what shell I changed to:

Code:

%bash
[devarish@m-net ~]$ echo $SHELL
/bin/sh

but I got the same output, i.e. /bin/sh.

Whereas the entry in /etc/passwd says a different story:

Code:

[devarish@m-net ~]$ grep ^$USER /etc/passwd
devarish:*:68166:10:Devarishi Kumar Mahadeva:/home/devarish:/usr/local/bin/menu
[devarish@m-net ~]$

So, how can we make sure from within a shell script that at any particular time or while that script is executing as to what shell the logged-in user is currently working in because echo $SHELL reports the same output even when the user has changed to some other shell temporarily?

Please note that we are not issuing the chsh command to change the shell permanently.

pwc101 · 01-04-2011, 09:36 AM

Code:

ps hp $$ | awk '{print $NF}'

devUnix · 01-04-2011, 09:59 AM

Quote:

Originally Posted by pwc101

Code:

ps hp $$ | awk '{print $NF}'

My question was long, your answer was short!

[1]

Code:

-bash-2.05b# ps p $$
  PID TTY      STAT   TIME COMMAND
 1389 pts/0    S      0:00 -bash
-bash-2.05b# ps p $$ | awk '{print $NF}'
COMMAND
-bash

[2]

Code:

-bash-2.05b# sh
sh-2.05b# ps p $$
  PID TTY      STAT   TIME COMMAND
 1827 pts/0    S      0:00 sh
sh-2.05b#

Thanks, Guru! I got it that echo $$ reports the current PID and when it is run on the Shell Prompt then it is the PID of the currently running Shell.

devUnix · 01-04-2011, 10:16 AM

Please see that when we change our current Shell to some other Shell then our Shell Script stops functioning as soon as it changes the current Shell and it resumes as soon as we exit from the changed Shell:

Source Script:

Code:

-bash-2.05b# cat > chkShell.sh
#!/bin/bash
echo "Parent Process:"
ps p $PPID
echo "Current Process:"
ps p $$
echo "Changing Shell to sh..."
sh
echo "Let us see where we are now:"
ps p $$
-bash-2.05b# chmod 755 chkShell.sh

Sample Run of the Script:

Code:

-bash-2.05b# chkShell.sh
Parent Process:
  PID TTY      STAT   TIME COMMAND
 1833 pts/0    S      0:00 -bash
Current Process:
  PID TTY      STAT   TIME COMMAND
 1961 pts/0    S      0:00 /bin/bash /root/bin/chkShell.sh
Changing Shell to sh...
sh-2.05b# echo $SHELL
/bin/bash
sh-2.05b# ps p $$
  PID TTY      STAT   TIME COMMAND
 1964 pts/0    S      0:00 sh
sh-2.05b# exit
exit
Let us see where we are now:
  PID TTY      STAT   TIME COMMAND
 1961 pts/0    R      0:00 /bin/bash /root/bin/chkShell.sh
-bash-2.05b#

So, how can we get out of the changed Shell from within the script itself without having to type "exit" at the command prompt?

I tried "exit" in the script but it didn't work. "return" would work only in a function and a sourced script.

Any ideas?

pwc101 · 01-04-2011, 10:59 AM

Err... I can't think of a way of doing this. Sorry.

edit: You may have better luck using expect.