A shell does much more than simply run commands. It also has
powerful features to make this task easier: wildcards for matching
filenames, a “command history” to recall previous commands quickly,
pipes for making the output of one command become the input of another,
variables for storing values for use by the shell, and more. Take the
time to learn these features, and you will become faster and more
productive. Let’s skim the surface and introduce you to these useful
tools. (For full documentation, run
Wildcards are a shorthand for sets of files with similar names.
a* means all files
whose names begin with lowercase “a.” Wildcards are “expanded” by the
shell into the actual set of filenames they match. So if you
the shell first expands
into the filenames that begin with “a” in your current directory, as
if you had typed:
ls aardvark adamantium apple
ls never knows you used a
wildcard: it sees only the final list of filenames after the shell
expands the wildcard. Importantly, this means
every command, regardless of its origin, works
with wildcards and other shell features.
Here’s an example of wildcard use. Suppose you have a folder containing hundreds of JPEG images from your digital camera, named IMG_1001.jpg through IMG_1864.jpg. You need to delete all the images ending in 20.jpg:
IMG_1020.jpg IMG_1120.jpg IMG_1220.jpg IMG_1320.jpg ...
The names of these files are not consecutive, nor are their dates, ...