notes: unix

Unix is user-friendly — it's just choosy about who its friends are.

The Art of UNIX Programming (2003) by Eric S. Raymond

Created in 1969 at AT&T Bell Labs to run on departmental computers for the PDP-11. It used 16-bit words and had 64KiB/128KiB RAM.

It was initially written in ASM, but sparked the creation of C which was designed to make Unix development easier.

Unix gives you just enough rope to hang yourself -- and then a couple of more feet, just to be sure.

Eric Allman

Philosophy

smaller kernel, a master process which provides services to system and user processes
a simple datatype (text) and simple interprocess communication
allows chaining of processes
seperation between ordinary users and superusers using privileges
files
almost everything is a file
- processes are files
- directories are files that point to other files
files are just sequences of bytes

filenames
extensions are conventional, not required
filenames can be any non-whitespace character (sus)
current dir is ., parent is ..
dotfiles are hidden
commands
<commandname> [<options>] [<objects>]
shell
the program that handles command interpretation
shell locates commands and objects
you can chain commands into shell scripts
- first was Bourne Shell sh in 1976
- followed by Bourne Again Shell bash in 1989
- Korn Shell ksh in 1983

Environment variables are defined by the system and will be will be passed to the shell.

system path is stored in env var PATH, list of dirs seperated by :, usually contains the following paths
/bin
- top level system commands
- cat, echo
/usr/bin
- system level commands that generally come with the system but may need to be installed
- python, gcc
- usr stands for Unix System Resources (though it originally meant user, since it used to be the user's directory, see The bin Split)
/usr/local/bin
- programs that you have installed for all users of your system locally
- pip3, ps2pdf
~/bin
- a users programs
.
- current directory
CDPATH
all locations that cd can direct you to
similar to PATH
PS1
shell prompt text
umask 077
permissions applied to files on creation

More environment variables can be setup in the ~/.profile executable.