The shell is both a command interpreter and a programming language. As a command interpreter, it executes commands you enter in response to its prompt. As a programming language, it executes commands from files called shell scripts. When you start a shell, it typically runs one or more startup files.
Running a shell script
When the file holding a shell script is in the working directory, there are three basic ways to execute the shell script from the command line.
1. Type the simple filename of the file that holds the script.
2. Type an absolute or relative pathname, including the simple filename preceded by ./.
3. Type bash or tcsh followed by the name of the file.
Technique 1 requires the working directory to be in the PATH ...