Glossary
Glob (wildcard)
Patterns like *.txt, expanded by the shell before the command runs.
Globs are filename patterns: * matches any sequence of characters, ? a single one, [abc] one of a set, and {a,b} expands to each alternative. Critically, the shell expands them against the filesystem before the command runs — ls *.txt hands ls a list of names, never an asterisk.
This explains why quoting matters: find . -name "*.txt" needs quotes so the pattern reaches find intact instead of being expanded by the shell first. Preview any glob by prefixing echo.
See it in practice
$ echo *.txt && find . -name "*.txt"Unquoted, the shell expands the pattern; quoted, find receives it intact and does its own matching. Same characters, different actor.
Where you'll meet it
Locate files anywhere in a directory tree by name, type, size, date — and act on them.
lsList the contents of a directory, with options for hidden files, long format, sorting and more.
echoPrint text and variables, and write or append to files with > and >>.
ShellThe program that reads your commands and runs them.