How can I specify many files at once?

Most shell commands will work on multiple files if you give them multiple filenames. For example, you can get the first column from all of the seasonal data files at once like this:

cut -d , -f 1 seasonal/winter.csv seasonal/spring.csv seasonal/summer.csv seasonal/autumn.csv

But typing the names of many files over and over is a bad idea: it wastes time, and sooner or later you will either leave a file out or repeat a file's name. To make your life better, the shell allows you to use wildcards to specify a list of files with a single expression. The most common wildcard is *, which means "match zero or more characters". Using it, we can shorten the cut command above to this:

cut -d , -f 1 seasonal/*

or:

cut -d , -f 1 seasonal/*.csv