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 ( 2.2 ) 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 (
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). [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 ./- |
$ |
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It's better to make a symbolic link ( 18.4 ) 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 ( 18.4 ) .) A third way is to write a little C program ( 52.8 ) 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:
$-csh
...normal C shell login process... % ...run whatever commands you want... %logout
$ ...back to original shell
Article 2.16 shows how this can be used to change your normal login shell.
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