shell scipts are files with `.sh` extension. It need to be executable to perform work.
create a file first.sh
first line is #! /bin/sh it gives link to bash shell residing in /bin for executing the script by sh tool.next line is echo tool with simple parameter of string. All the lines starting with # are comments which will be not executed by shell. semicolon is not mandotry unless multiple commands are used in a single line.
Now close the file. file need to be given executable permission. `chmod +x first.sh` gives executable permission. Now call the file by name `./first.sh` to execute.
There is another method to execute by passing file to sh command. `sh first.sh` command executes first.sh by sh tool and gives output in console.