I found the .bashrc file and I want to know the purpose/function of it. Also how and when is it used?

up vote 99 down vote accepted

.bashrc is a shell script that Bash runs whenever it is started interactively. It initializes an interactive shell session. You can put any command in that file that you could type at the command prompt.

You put commands here to set up the shell for use in your particular environment, or to customize things to your preferences. A common thing to put in .bashrc are aliases that you want to always be available.

.bashrc runs on every interactive shell launch. If you say:

$ bash ; bash ; bash

and then hit Ctrl-D three times, .bashrc will run three times. But if you say this instead:

$ bash -c exit ; bash -c exit ; bash -c exit

then .bashrc won't run at all, since -c makes the Bash call non-interactive. The same is true when you run a shell script from a file.

Contrast .bash_profile and .profile which are only run at the start of a new login shell. (bash -l) You choose whether a command goes in .bashrc vs .bash_profile depending on on whether you want it to run once or for every interactive shell start.

As a counterexample to aliases, which I prefer to put in .bashrc, you want to do PATH adjustments in .bash_profile instead, since these changes are typically not idempotent:

export PATH="$PATH:/some/addition"

If you put that in .bashrc instead, every time you launched an interactive sub-shell, :/some/addition would get tacked on to the end of the PATH again, creating extra work for the shell when you mistype a command.

You get a new interactive Bash shell whenever you shell out of vi with :sh, for example.

  • 5
    Minor quibble: unlike most other shells, bash does not automatically load the per-instance config file .bashrc when it's started as a login shell. This can sometimes lead to unexpected behavior. The usual workaround is to source .bashrc from .profile or .bash_profile instead. – Ilmari Karonen May 13 '14 at 11:14
  • @IlmariKaronen Since .bashrc isn't intended for use by other shells, it's better not to source it from .profile (which might be used by other non-bash shells). – chepner May 14 '14 at 2:32
  • @IlmariKaronen what happens (read: how can I debug why) when source ~/.bashrc or . ~/.bashrc or [[ -f ~/.bashrc ]] && source. ~/.bashrc or [ -f ~/.bashrc ] && source ~/.bashrc don't work? – Nikos Alexandris Feb 12 '17 at 14:22
  • @NikosAlexandris: That's a separate question. Please ask it separately. – Warren Young Feb 12 '17 at 14:36
  • @WarrenYoung I would but I realised that .bashrc is indeed sourced (using the recommended command from superuser.com/a/183980/128768). The problem I face is actually the not sourcing of https://github.com/junegunn/fzf via this command inside .bashrc: source ~/.fzf.bash. I launch a new terminal, then Ctrl+R and I get `__fzf_history__`bash: fzf: command not found. I source manually .bashrc and the same key shortcut launches fzf as expected. Apologies for the noise here. – Nikos Alexandris Feb 12 '17 at 15:46

The purpose of a .bashrc file is to provide a place where you can set up variables, functions and aliases, define your (PS1) prompt and define other settings that you want to use every start you open a new terminal window.

It works by being run each time you open up a new terminal, window or pane.

You can see mine here (pic with syntax highlighting):

HISTCONTROL=ignoreboth:erasedups HISTSIZE=100000 HISTFILESIZE=200000
ls --color=al > /dev/null 2>&1 && alias ls='ls -F --color=al' || alias ls='ls -G'
md () { [ $# = 1 ] && mkdir -p "$@" && cd "$@" || echo "Error - no directory passed!"; }
git_branch () { git branch 2> /dev/null | sed -e '/^[^*]/d' -e 's/* \(.*\)/\1/'; }
HOST='\033[02;36m\]\h'; HOST=' '$HOST
TIME='\033[01;31m\]\t \033[01;32m\]'
LOCATION=' \033[01;34m\]`pwd | sed "s#\(/[^/]\{1,\}/[^/]\{1,\}/[^/]\{1,\}/\).*\(/[^/]\{1,\}/[^/]\{1,\}\)/\{0,1\}#\1_\2#g"`'
BRANCH=' \033[00;33m\]$(git_branch)\[\033[00m\]\n\$ '
PS1=$TIME$USER$HOST$LOCATION$BRANCH
PS2='\[\033[01;36m\]>'
set -o vi # vi at command line
export EDITOR=vim
test -f ~/.bash_aliases && . $_
test -f ~/.git-completion.bash && . $_
test -s ~/.autojump/etc/profile.d/autojump && . $_
[ ${BASH_VERSINFO[0]} -ge 4 ] && shopt -s autocd
[ -f /etc/bash_completion ] && ! shopt -oq posix && . /etc/bash_completion
[ -z $TMUX ] && export TERM=xterm-256color && exec tmux
export PATH="$PATH:$HOME/.rvm/bin" # Add RVM to PATH for scripting
[[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$home/.rvm/scripts/rvm"

Explanation:

-1. Set up my history file to ignore duplicates and be much larger than the default.
-2. Color option for ls depending on if you are using linux or OSX
-3. Function "md" to make and cd into a directory with one command
-4. Find the current git branch if in a git repo and...
-5. -9. Define an awesome PS1 prompt, as in <code>20:00:43 durrantm Castle2012 /hom/durrantm/Dropnot/_/rails_apps/linker master \n $ _</code>
-10. Improved PS2 prompt
-11. Set vi as the editor at the command line
-12. Set vi as the default editor
-13. execute my .bash_aliases file if it exists
-14. Execute my git tab completion script (for remotes and branches) if it exists.
-15. Execute autojump if it exists
-16. Allow cd'ing without typing the cd part if the bash version >= 4
-17. Execute a bash completion script if it exists
-18. Use TMUX if it is present
-19. Add rvm to my PATH
-20. Use rvm if it exists.

I've made this portable so that it works on any of my linux or OSX machines without customization - hence a number of tests for presence are done before using certain functions and other scripts.

This also makes it easier to use the entire file immediately on a new machine without having issues that affect opening a new terminal window.

  • Overkill...       ͏͏͏͏͏͏͏͏͏ – Pacerier Nov 2 '17 at 13:42
  • huh? too helpful for you? – Michael Durrant Nov 3 '17 at 2:12
  • 1
    Thank you SO much for sharing. A wealth of information here. – Vic Jul 3 at 15:28

It is a bash config file.

Interactive (non-login) shells, then the config is read from these files:

  • $HOME/.bashrc

For Login shells, the config is read from these files:

  • /etc/profile (Always sourced)
  • $HOME/.bash_profile (the rest of these files are checked in order until one is found, then no others are read)
  • $HOME/.bash_login
  • $HOME/.profile

Simple illustration of how/when they are loaded is in the image below.

I added an echo to my .bashrc and .bash_profile

Interactive shell vs login shell

see man bash for more information

  • 2
    This doesn't really add additional value to an old question. Also, I see that you're new to Unix & Linux, try not to post pictures of text, instead it's better to use the code block formatting and copy from your console. This allows the text to be searched/copied/etc. In the case of your example there aren't really any complicated commands or anything that would be good to search, but a good practice for other answers. – Centimane Sep 15 '16 at 18:24
  • 1
    I'm not sure I fully understand your reference to 'old question' It is in the top question list, and it is relevant with 60k views. I thought the added value came from the format, as opposed to a dialog/conjecture like the previous answers. but the format has been edited as well. I will keep in mind your comments about using code blocks, thanks. – Timothy L.J. Stewart Sep 15 '16 at 19:31
  • 1
    It's in the top of the 'active' question list because you posted an answer. The question was originally asked in 2014, and accepted an answer. The accepted answer states the purpose of .bashrc and distinguishes the difference between .bashrc and .bash_profile which covers the content of your answer. Don't be discouraged, you put forward an honest effort, but try to focus on answering questions with some content not covered by other answers. – Centimane Sep 15 '16 at 19:36

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