In a graphical system, mostly a non-login shell is used by a user. To run a non-login shell, we don't need the login credentials. Starting a shell in a graphical system provides a non-login shell. When a bash is invoked in non-login mode, the ~/.bashrc file is invoked and the configuration available in it is executed and applied in any bash shell being launched. Settings that are needed in both the login and non-login shell are kept in the ~/.bashrc file.

For example, on a Fedora 22 system default, the ~/.bashrc file looks as follows:

# .bashrc

# Source global definitions
if [ -f /etc/bashrc ]; then
        . /etc/bashrc
fi

# Uncomment the following line if you don't like systemctl's auto-paging feature:
# export SYSTEMD_PAGER=

# User specific aliases and functions

Any addition done in ~/.bashrc will be reflected only to the current user's bash shell. We can see that the .bashrc file also checks whether the etc/bashrc file is available. If available, that gets executed too. The /etc/bashrc file contains configuration applied to a bash shell for all users—that is, systemwide. Sysadmin can modify the /etc/bashrc file if any configuration needs to be applied to all users' bash shells.

The file /etc/bashrc also looks into the script files available in /etc/profile.d, which can be confirmed by the following code snippet taken from the /etc/bashrc file:

 for i in /etc/profile.d/*.sh; do
        if [ -r "$i" ]; then
            if [ "$PS1" ]; then
                . "$i"

The following example shows a modified .bashrc file. Name this file custom_bashrc:

# custom_bashrc

# Source global definitions
if [ -f /etc/bashrc ]; then
        . /etc/bashrc
fi

# Uncomment the following line if you don't like systemctl's auto-paging feature:
# export SYSTEMD_PAGER=

# User added settings
# Adding aliases
alias rm='rm -i'  # Prompt before every removal
alias cp='cp -i'  # Prompts before overwrite
alias df='df -h'  # Prints size in human readable format
alias ll='ls -l'  # Long listing of file

# Exporting environment variables
# Setting and exporting LD_LIBRARY_PATH variable
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:~/libs
# Setting number of commands saved in history file to 10000
export HISTFILESIZE=10000

# Defining functions
# Function to calculate size of current directory
function current_directory_size()
{
echo -n "Current directory is $PWD with total used space "
du -chs $PWD 2> /dev/null | grep total | cut -f1
}

The LD_LIBRARY_PATH environment variable is used to give the runtime shared library loader (ld.so) an extra set of directories to look for when searching for shared libraries. You can learn more about the shared library at http://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html.

Make a backup of your original ~/.bashrc file before modifying it:

$ cp ~/.bashrc ~/.bashrc.bak

Now, copy the custom_bashrc file to ~/.bashrc:

$ cp custom_bashrc ~/.bashrc

To apply modified settings, open a new bash shell. To apply a new .bashrc in the same bash shell, you can source into a new ~/.bashrc file:

$ source ~/.bashrc

We can check whether the new settings are available or not:

$ ll /home  # Using alias ll which we created

total 24
drwx------.  2 root    root    16384 Jun 11 00:46 lost+found
drwx--x---+ 41 foo  foo      4096  Aug  3 12:57 foo

$ alias  # To view aliases

alias cp='cp -i'
alias df='df -h'
alias ll='ls -l'
alias ls='ls --color=auto'
alias rm='rm -i'
alias vi='vim'

The alias command displays aliases that we added in .bashrc—that is, rm, cp, df, and ll.

Now, call the current_directory_size()function that we added in .bashrc:

$ cd ~	# cd to user's home directory
$ current_directory_size
Current directory is /home/foo with total used space 97G
$ cd /tmp
$  current_directory_size
Current directory is /tmp with total used space 48K

Make sure to move back the original .bashrc file whose backup we created at the beginning of this example, and source into it to get the settings reflected in the current shell session. This is required if you don't want any of the configuration changes that we did while playing out the preceding example:

$ mv ~/.bashrc.bak ~/.bashrc
$ source ~/.bashrc

In a non-graphical system, after a successful login, the user gets a shell. Such a shell is called a login shell. When a bash is invoked as a login shell, first the /etc/profile file gets executed; this runs the script available in /etc/profile.d/ as well. The following code snippet taken from /etc/profile also mentions this:

for i in /etc/profile.d/*.sh ; do
    if [ -r "$i" ]; then
        if [ "${-#*i}" != "$-" ]; then 
            . "$i"
        else

These are global settings applied to any user's login shell. Furthermore, ~/.bash_profile gets executed for a login shell. On a Fedora 22 system, the default content of the ~/.bash_profile file looks as follows:

# .bash_profile

# Get the aliases and functions
if [ -f ~/.bashrc ]; then
        . ~/.bashrc
fi

# User specific environment and startup programs

PATH=$PATH:$HOME/.local/bin:$HOME/bin

export PATH

From the contents, we can see that it looks for the .bashrc file in a user's home directory. If the .bashrc file is available in a home directory, it gets executed. We also know that the ~/.bashrc file executes the /etc/bashrc file as well. Next, we see that .bash_profile appends the PATH variable with the $HOME/.local/bin and $HOME/bin values. Furthermore, the modified PATH variable is exported as an environment variable.

A user can modify the ~/.bash_profile file as per his/her customized configuration needs, such as default shell, editor for login shell, and so on.

The following example contains a modified configuration in .bash_profile. We will use bash_profile as its filename:

# .bash_profile

# Get the aliases and functions
if [ -f ~/.bashrc ]; then
        . ~/.bashrc
fi

# User specific environment and startup programs

PATH=$PATH:$HOME/.local/bin:$HOME/bin

export PATH

# Added configuration by us
# Setting user's default editor
EDITOR=/usr/bin/vim
# Show a welcome message to user with some useful information
echo "Welcome 'whoami'"
echo "You are using $SHELL as your shell"
echo "You are running 'uname ' release 'uname -r'"
echo "The machine architecture is 'uname -m'"
echo "$EDITOR will be used as default editor"
echo "Have a great time here!"

Changes are made after the Added configuration by us comment. Before we apply this new configuration to ~/.bash_profile, we will first make a backup of the original file. This will help us in restoring the original content of the .bash_profile file:

$ cp ~/.bash_profile ~/.bash_profile.bak

A new file .bash_profile.bak will be created in the home directory. Now, we will copy our new configuration to ~/.bash_profile:

$ cp bash_profile ~/.bash_profile

To see the reflected changes in a login shell, we can either login as a non-graphical interface or just perform ssh into the same machine to run a login shell. SSH (Secure Shell) is a cryptographic network protocol for initiating text-based shell sessions on remote machines in a secure way. In UNIX and Linux-based systems, SSH to a local or remote machine can be done using the ssh command. The man page of ssh (man ssh) shows all the capabilities provided by it. To do a remote login on the same machine, we can run ssh username@localhost:

$ ssh foo@localhost    #  foo is the username of user

Last login: Sun Aug  2 20:47:46 2015 from 127.0.0.1
Welcome foo
You are using /bin/bash as your shell
You are running Linux release 4.1.3-200.fc22.x86_64
The machine architecture is x86_64
/usr/bin/vim will be used as default editor
Have a great time here!

We can see that all the details added by us are printed in a login shell. Another way to quickly test our new .bash_profile is by doing source to it:

$ source ~/.bash_profile

Welcome foo
You are using /bin/bash as your shell
You are running Linux release 4.1.3-200.fc22.x86_64
The machine architecture is x86_64
/usr/bin/vim will be used as default editor
Have a great time here!

To reset changes done in the ~/.bash_profile file, copy from the ~/.bash_profile.bak file that we created at the beginning of this example and source into it to get the changes reflected in the current shell:

$ mv ~/.bash_profile.bak ~/.bash_profile
$ source ~/.bash_profile

The .bash_logout file present in a user's home directory gets executed every time a login shell exits. This is useful when a user has logged in remotely or has a non-graphical interface. A user can add clean-up tasks to be performed before he/she logs off from a system. A clean-up task may include removing the temporary files created, clearing environment variables, logging off important data, archiving or encrypting certain tasks, uploading onto the Web, and so on.