In this section, we will continue to talk about content representation in Unix, and we will look at how we can effectively name files, particularly, when we have large numbers of files that are of a particular type. So, if we're looking at the content of the current directory for our application, LS would show us that we have three types of files for each of the three species. The three species are apple, peach, and pear, and for each of the species, we have a genome file, a genes file and a samples file. So that's simple, right? But now, let's imagine that we have 100 species, and that we have 1,000 files for each one. Well, how can we represent, or how can we least files, in that case efficiently? We can use the so called naming patterns. We can use wild cards. For instance, one very popular wild card, and very useful one, is the star. So star represents any combination of letters and numbers, so any string. So we can very simply type now, list all the fives that are associated with the species apple, apple.star, and that would give us the three files that correspond to the species apple, apple.genes, apple.genome, and apple.samples. And we can do so with the other species as well. Another wild card, that now stands for just one character, is marked with a question mark. So, for instance, we can say ls ?pple.genome, and this will return apple.genome. So, as you can see, the question mark stands for the a at the beginning of file name. We can also represent a range of characters in square brackets. So we can say, square brackets, any lower case letter between A and Z, multiple times, and this what star stands for, .genome. So this is a representation that will give us all the files that have the extension genome. Apple.genome, peach.genome, and pear.genome. We can also do combinations. So for instance, we can look at all the genomes files whose name starts with the letter P. LS p star .genome, and that will give us peach.genome and pear.genome. Lastly, there's one more way of representing one more naming pattern that I would like to show you, which is the curly brackets. So in curly brackets, we can specify a number of options. So we can say, ls open curly bracket pear, peach.genome, and it will list all the files that have either pear or peach at the beginning of the file name, followed by .genome. So in this case, peach.genome and pear.genome. So this way we can represent a very large number of files that share a common naming pattern in a very effective way.
