Initialization files and file editing

Initialization files and configuration

  • When the shell first starts (when you login), it reads some files. These are normal shell files, and it evaluates normal shell commands to set configuration.

  • You can always test things in your own shell and see if it works before putting it in the config files. Highly recommended!

  • You customize your environment means setting or expanding aliases, variables, functions.

  • The config files are:

    • .bashrc (when SSH) and

    • .bash_profile (interactive login to a workstation)

    • they are often a symlink from one to another

  • To get an idea how complicated .bashrc can be take a look at <>

One of the things to play with: command line prompt defined in PS1 [1]

PS1="[\d \t \u@\h:\w ] $ "

For special characters see PROMPTING at man bash. To make it permanent, should be added to .bashrc like export PS1.

Creating/editing/viewing file

  • A text editor edits files as ASCII. These are your best friend. In fact, text files are your best friend: rawest, most efficient, longest-lasting way of storing data.

  • “pager” is a generic term for things that view files or data.

Linux command line text editors like:

  • nano - simplest

  • vim - minimal. To save&quit, ESC :wq

  • emacs - or the simplest one nano. To save&quit: Ctrl-x Ctrl-c

To view contents of a file in a scrollable fashion: less

Quick look at the text file cat filename.txt (dumps everything to screen- beware of non-text binary files or large files!)

Other quick ways to add something to a file (no need for an editor)

echo 'Some sentence, or whatever else 1234567!-+>$#' > filename.txt

cat > filename2.txt to finish typing and write written to the file, press enter, then Ctrl-d.

The best text viewer ever less -S (to open a file in your EDITOR, hit v, to search through type /search_word)

Watching files while they grow tail -n 0 -f <file>

Try: add above mentioned export PS1 to .bashrc. Remember source .bashrc to enable changes

Exercise 1.5


  • link .bash_profile to .bashrc. Tip: see ln command from the previous session.

  • add umask 027 to .bashrc, try creating files. Tip: umask -S prints your current setting.

  • customize a prompt $PS1 and add it to your .bashrc, make sure is has a current directory name and the hostname in it in the format hostname:/path/to/current/dir. Hint: save the original PS1 like oldPS1=$PS1 to be able to recover it any time.