Linux Shells by Example

9.1. Introduction

When commands are executed from within a file, instead of from the command line, the file is called a shell script and the shell is running noninteractively. When the bash shell starts running noninteractively, it looks for the environment variable, BASH_ENV (ENV) and starts up the file (normally bashrc) assigned as its value. After the BASH_ENV file has been read, the shell will start executing commands in the script.^[1]

^[1] when bash starts interactively, in the -norc or --norc option is given, the BASH_ENV or ENV file will not be read.

9.1.1. The Steps in Creating a Shell Script

A shell script is normally written in an editor and consists of commands interspersed with comments. Comments are preceded by a pound sign and consist ...