Shell Commands

The Shell is a tool for setting up the environment for a program to run.

This includes:

• The initial working directory
• The std in, out, err streams
• environment variables such as "USER=XXX", "HOME=/XXX/XXX"
• User id

sh is a lightweight scripting language and can be used for configuration

sort < foo.txt | sed 's/a/b/' | grep back

Behind the scene, the 3 functions each runs in their own enviornment

foo.txt → sort → pipe → sed → piple → grep

A simple shell command

grep abc def ghi

In a high level picture, shell rearrange and configure the program to execute the functions

The shell doesn't care which of the strings are file names or pattern

Quoting