[Chapter 51] 51.9 Making a "Login" Shell
Author: Jerry Peek, Tim O'Reilly & Mike Loukides
Date: 1998-08-04T21:57:27Z

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| Chapter 51 Miscellaneous Useful Programs and Curiosities |

## 51.9 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 (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 (`-`). [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
    ./-
    $ cd $HOME/bin
    $ cp /bin/csh ./-csh

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.

- JP

51.8 Type Bang Splat. Don't Forget the Rabbit Ears |  | 51.10 The date Command