1 Startup Files: .bash_profile and .bashrcIndex

Loading shell defaults, options, aliases, the prompt, and functions is done when the shell first starts. You can change things while the shell is running, but the changes are not saved. Start-up files are places to save things so that every new shell gets them.

All startup file references are to files in your home directory, which is where cd takes you without arguments. Your home directory is also usually available in the environment variable $HOME.

Your start-up files are not re-read by your current shell after you edit them - you have to tell your current BASH shell to re-read them to make the new content take effect in the current shell, e.g. $ source ./.bashrc

2 $HOME/.bash_profileIndex

If you use a Linux system (e.g. RedHat, Knoppix, Ubuntu, Fedora, SuSE, etc.), your login shell is already BASH and it reads (“sources”) the .bash_profile file when you log in. The .bash_profile is only read once by the login shell, not by any other non-login shells you might start up after you log in.

The .bashrc file is not read by a login shell, so most people put source ./.bashrc in their .bash_profile.

You can put things in .bash_profile that need to be done exactly once when you log in and that are inherited by other shells:

• set (and export) PATH and/or TERM
• set umask
• set your erase character (backspace character)
• set your prompt PS1 (and export it:  export PS1)

Any aliases you define in these login profile files will apply only to the BASH shell at login, not to any other shells you start. It is usually better to define aliases in your $HOME/.bashrc file and use source ./.bashrc in the .bash_profile.

If you find that a nested shell is not inheriting PATH, TERM, or PS1, you must “export” the variable, e.g. “export PS1”.

To define aliases and shell options that cannot be exported or inherited, use the other start-up file .bashrc:

Your start-up files are not re-read by your current shell after you edit them - you have to tell your current BASH shell to re-read them to make the new content take effect in the current shell, e.g. $ source ./.bash_profile

3 $HOME/.bashrcIndex

Put things in your .bashrc that don’t get exported or inherited from parent shells and that must be set new for each new shell, such as aliases and shell options.

Every non-login BASH shell reads (“sources”) .bashrc when it first starts up. Every new non-login BASH shell reads this file, unless you use the “--norc” option when you start it.

Any aliases and options you define in .bashrc will apply to all BASH shells, except your login shell that sources .bash_profile instead.

The .bashrc file is not read by a login shell, so most people put source ./.bashrc in the .bash_profile.

Set your personal BASH aliases and functions in the .bashrc file, e.g. alias cd..='cd ..'

Set your own useful shell options in your .bashrc; I recommend these:

• shopt -s failglob
• set -o ignoreeof -o noclobber -o notify -o nounset
• set -o physical -o interactive-comments

shopt -s failglob

Give an error message if a GLOB fails to match any pathnames, instead of silently returning the GLOB pattern unchanged.

set -o ignoreeof

The shell will ignore ^D (EOF) at the prompt; use “exit” to exit.

set -o noclobber

Protects files from being overwritten when “>” redirection is used. Use the “force” syntax “>|” (that’s a pipe character) to force overwriting, e.g. date >| file

set -o notify

Notifies user immediately when a background job (started with “&” or bg) completes. Without this, you won’t be told that the background job is done until you push ENTER.

set -o nounset

Displays an error when expanding a variable that has not been set. Essential for detecting typing errors in variable names.

set -o physical

Expand all symbolic links in output of pwd and when using cd so that you see the real directory names and paths. Essential for system administrators to know exactly where you are in the file system.

set -o interactive-comments

Allow “#” to comment out any following text when typed interactively, e.g. echo a b # this text is not seen

Refer to the BASH man page for details on these options.

Your start-up files are not re-read by your current shell after you edit them - you have to tell your current BASH shell to re-read them to make the new content take effect in the current shell, e.g. $ source ./.bashrc

alias l='less'
alias mv='mv -i'
alias cp='cp -i -p'
alias ls='ls -abp --color=auto'
alias grep='grep --color=auto'

export HISTSIZE=2000
export HISTFILESIZE=1000000
export HISTCONTROL=ignoredups
export HISTTIMEFORMAT=
shopt -s cmdhist
shopt -s histappend

4 What happens when you Log In?Index

When you type in your user name (userid) and password to log in, the system encrypts your password and compares it against the encrypted password in the password files. If they match, you are allowed to log in.

At log-in time, the system sets your current directory to be the HOME directory listed for your account in the password file. An initial environment is prepared (e.g. containing a system default PATH).

For a text command-line (terminal or console) log in, the shell specified in the password file is executed. (This shell is usually /bin/bash.)

For a graphical log-in, a window manager is started and your Desktop is initialized for display.

If your login shell is /bin/bash, the BASH process reads (“sources”) some system start-up files such as /etc/profile and /etc/bash.bashrc that may set system defaults for various Environment Variables.

Next, a login shell looks in your home directory for more start-up files such as .bash_profile or .bash_login that you can use to alter the system defaults. (See “man bash” for the full list.) You can create your own initialization files to customize your environment and terminal settings.

(Some systems give default .bash_login and .bash_logout files when you create a new account. The default files are copied from a system directory such as /etc/skel.)

5 Non-interactive shells and PS1Index

Do not set the PS1 prompt string in any start-up file unless it is already set, indicating an interactive shell. Do not produce any output in any start-up file unless the shell is interactive (has PS1 set non-empty).

Non-interactive shells do not set a prompt, and these shells must not generate prompts or output when they run. Programs transferring files to/from your account depend on non-interactive shells executing without generating any unexpected output.

You can check to see if your shell is generating any unexpected output by using ssh to execute the true command (or any command that generates no output) and watching for any output after you enter your password:

$ ssh localhost true
*** COURSE LINUX SERVER ***
user@localhost's password: 
Welcome back gracious Lord of All.
$ 

The above “Welcome” line output from an echo command inside a .bashrc will cause file transfer programs to fail.

To prevent the rest of a .bashrc from running if the shell is not interactive, insert this line at the start of the file (make sure you type this as shown, including the spaces):

[ -z "$PS1" ] && return

The above line will skip the rest of the file if the shell is not being used interactively. The result will be no unexpected output when a shell is used non-interactively. You can test this using a command that produces no output, such as true or cd, and making sure that no output appears:

$ ssh localhost true
*** COURSE LINUX SERVER ***
user@localhost's password: 
$ 

Above, there is no unexpected output from the non-interactive shell, but if you fully log in and the shell is interactive, the .bashrc runs normally and generates the expected output:

$ ssh localhost
*** COURSE LINUX SERVER ***
user@localhost's password: 
Welcome back gracious Lord of All.
YesMaster$ exit
exit
$