How to get default shell

you can use the following command echo $SHELL

For macOS:

dscl . -read /Users/username UserShell

For the current macOS user:

dscl . -read ~/ UserShell

To parse the path inline using sed:

dscl . -read ~/ UserShell | sed 's/UserShell: //'

Using $SHELL will report the current login shell, not the default login shell. In certain cases, these are not the same. For example, when working in an IDE such as Visual Studio Code which opens an integrated terminal without consulting the default shell.

In addition, as pointed out by Martin C. Martin, $SHELL is a constant that will not change after chsh changes the default login shell.

You can grep in the /etc/passwd file for current username, and use cut to extract the appropriate column of information:

grep ^$(id -un): /etc/passwd | cut -d : -f 7-

$(id -un) is a safer than $USER to get user name. Using ^ in front of user name and : after makes sure you don't get a false match if your user name is a sub section of someone else user name.

$SHELL can also be used, as suggested. However it won't work if chsh was used in current shell, as the variable is not updated. Also the variable is not protected against being changed, so it can theoretically be set to something completely different.

Update to attempt an OS X compatible solution. Probably not optimal regexp:

grep ^.*:.*:$(id -u): /etc/passwd | cut -d : -f 7-

This is based on user id's. If the whole user entry is missing, not only user name, then osx must store this somewhere else.