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A shell script is a reusable series of commands put in an executable text file. Any text editor can be used to write scripts.
Scripts start with #! followed by the path to the shell executing the commands from the script. Comments are added to a script for your own future reference, and also to make it understandable for other users. It is better to have too many explanations than not enough.
Debugging a script can be done using shell options. Shell options can be used for partial debugging or for analyzing the entire script. Inserting echo commands at strategic locations is also a common troubleshooting technique.