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key points:

• A for loop repeats commands once for every thing in a list.
• Every for loop needs a variable to refer to the thing it is currently operating on.
• Use $name to expand a variable (i.e., get its value). ${name} can also be used.
• Do not use spaces, quotes, or wildcard characters such as ‘*’ or ‘?’ in filenames, as it complicates variable expansion.
• Give files consistent names that are easy to match with wildcard patterns to make it easy to select them for looping.
• Use the up-arrow key to scroll up through previous commands to edit and repeat them.
• Use Ctrl+R to search through the previously entered commands.
• Use history to display recent commands, and ![number] to repeat a command by number.