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

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2 Answers 2

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.bashrc is a shell script that Bash runs whenever it is started interactively. 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.

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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 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 at 2:32

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:enter image description here

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 enter image description here
-10. Improved PS2 prompt
-11. Set vi as the editor at the command line
-12. Set vi as the default editor
-13. execute my 1.bash_aliases1 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.

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