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key points:

• Save commands in files (usually called shell scripts) for re-use.
• bash [filename] runs the commands saved in a file/
• $@ refers to all of a shell script’s command-line arguments.
• $1, $2, etc., refer to the first command-line argument, the second command-line argument, etc.
• Place variables in quotes if the values might have spaces in them.
• Letting users decide what files to process is more flexible and more consistent with built-in Unix commands.