Making a "Login" Shell
When you log in to most UNIX systems, your shell is a login shell. When a shell is a login shell, it acts differently. For example, the shell reads a special setup file () like profile or login. UNIX "knows" how to tell the shells to be login shells. If you type the shell's name (like sh or /bin/csh) at a prompt, that will not start a login shell.
Sometimes, when you're testing an account or using a window system, you want to start a login shell without logging in. UNIX shells act like login shells when they are executed with a name that starts with a dash (-). [1] The easiest way to do this, which wastes a lot of disk space (and may not work on your system anyway if the shells are read-protected), is to make your own copy of the shell and name it starting with a dash:
[1] bash also has a command-line option, -login, that makes it act like a login shell.
bin /- |
$ |
|---|
It's better to make a symbolic link () to the shell:
$cd $HOME/bin$ln -s /bin/csh ./-csh
(Or, if your own bin subdirectory is on the same filesystem as /bin, you can use a hard link ().) A third way is to write a little C program () that runs the actual shell but tells the shell that its name starts with a dash. This is how the UNIX login process does it:
main() {
execl("/bin/csh", "-csh", 0);
}
No matter which way you choose, you can execute your new shell by typing its name:
$-cshnormal C shell login process... % run whatever commands you want... %logout$ back to original shell
Article shows how this can be used to change your normal login shell.
- JP