What the shell does before running a command.
WHAT EXPANSION MEANS
The shell rewrites your command before the program ever sees it.
WHY THAT MATTERS
The program receives a list of filenames, not the pattern you typed.
WHAT AN ASTERISK MATCHES
Any sequence of characters, including none.
WHAT A QUESTION MARK MATCHES
Exactly one character.
WHAT SQUARE BRACKETS MATCH
Any one character from a set or range.
WHAT BRACE EXPANSION DOES
Generates a list from a pattern.
WHERE THAT HELPS
Creating several directories at once, or copying a file to a backup name in one step.
WHAT A DOT-PREFIXED FILE IS NOT MATCHED BY
A plain asterisk.
WHY THAT SURPRISES PEOPLE
Copying everything with an asterisk silently omits hidden files, which is most configuration.
WHAT HAPPENS WHEN NOTHING MATCHES
The pattern is passed through literally, in most shells.
WHY THAT CAUSES CONFUSION
A command receives a literal asterisk and reports a file not found with that name.
WHAT TO DO BEFORE ANY DESTRUCTIVE COMMAND WITH A WILDCARD
Run ls with the same pattern and read the output.
WHY
It shows exactly what the command will act on.
WHAT TO NEVER DO
Put a space between a path and an asterisk unintentionally.
WHY
Deleting a directory and everything in the current one are one keystroke apart.
