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Let's say, i opened a terminal and entered/executed some shell commands.

But i didnt invoke explicitly bash or any other shell.

What shell was used by default?

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4 Answers

The one specified on your line in /etc/passwd (it is a : separated line and the shell is the final one).

For example mine:

chris:x:1000:1000:Chris,,,:/home/chris:/bin/bash

Here it is /bin/bash (the Ubuntu default)

You can also use chsh:

$ chsh
Password: 
Changing the login shell for chris
Enter the new value, or press ENTER for the default
        Login Shell [/bin/bash]:

This is telling me my shell is /bin/bash and letting me change it.

Finally, echo $SHELL will do the same:

$ echo $SHELL
/bin/bash
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if it's bash, why is it sometimes invoked explicitly like sudo bash -c "netstat -an | grep LISTEN | grep -v ^unix" ?? –  DrStrangeLove Dec 14 '11 at 23:25
    
I think that's a bad command personally - none of that even requires root. If it did, it would be better written as sudo netstat -an | grep LISTEN | grep -v ^unix. I see no reason to enclose that in a bash subshell. –  Caesium Dec 14 '11 at 23:30
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@DrStrangeLove: If more than one command in the pipe needed root permissions, then sudo bash -c "..." would ensure that the entire pipe is executed by root. –  Keith Thompson Dec 15 '11 at 0:51
    
If you don't know which commands require root (and why), you shouldn't run them. Otherwise, why trust any command/program/script any more than is required. If you can't commandA | sudo commandB | commandC, you could do a sudo id first (runs the id command as root, but also acquires a "use sudo without password prompt" token that lasts for (default) 15 minutes. –  waltinator Dec 20 '11 at 4:10
    
Duh! sudo -v refreshes the token without all the effort of running id. –  waltinator Dec 20 '11 at 4:25
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GNU Bash is the shell used by default in terminals on Ubuntu. However when scripts are executed on system boot then dash is used, as it is dash that is /bin/sh.

This is defined in the $SHELL environmental variable. You can check by typing echo $SHELL in the terminal.

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+1 great answer (remembering dash)! –  user8290 Dec 14 '11 at 23:48
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typing the following will display what shell the terminal opened with:

echo $SHELL

However, to find out what shell you are currently in (you may have changed it) type

ps -p $$

e.g. you will see that the shell is bash in the example output

  PID TTY          TIME CMD
 3500 pts/0    00:00:01 bash

Another method is to use

echo $0

this will simply return the name of the current shell.

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By default it's bash:

env | grep SHELL

Produces

SHELL=/bin/bash
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Not necessarily. If you create a new user with useradd, it defaults to sh. $ useradd -D|grep SHELL SHELL=/bin/sh. –  Sparhawk Apr 10 at 6:48
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