As stated, glob commands achieve a similar effect to regular expressions. There are some differences though. For example, the * character in regular expressions stood for zero or more occurrences of the preceding character. For globbing, it is a wildcard for any and all characters, more similar to the .* notation of regular expressions.

As with regular expressions, a glob pattern can consist of normal characters, combined with special characters. Take a look at an example where ls is used with different arguments/globbing patterns:

reader@ubuntu:~/scripts/chapter_09$ ls -l
total 68
-rw-rw-r-- 1 reader reader  682 Oct  2 18:31 empty-file.sh
-rw-rw-r-- 1 reader reader 1183 Oct  1 19:06 file-create.sh
-rw-rw-r-- 1 reader reader  467 Sep 29 19:43 functional-check.sh
<SNIPPED>
reader@ubuntu:~/scripts/chapter_09$ ls -l *
-rw-rw-r-- 1 reader reader  682 Oct  2 18:31 empty-file.sh
-rw-rw-r-- 1 reader reader 1183 Oct  1 19:06 file-create.sh
-rw-rw-r-- 1 reader reader  467 Sep 29 19:43 functional-check.sh
<SNIPPED>
reader@ubuntu:~/scripts/chapter_09$ ls -l if-then-exit.sh 
-rw-rw-r-- 1 reader reader 416 Sep 30 18:51 if-then-exit.sh
reader@ubuntu:~/scripts/chapter_09$ ls -l if-*.sh
-rw-rw-r-- 1 reader reader 448 Sep 30 20:10 if-then-else-proper.sh
-rw-rw-r-- 1 reader reader 422 Sep 30 19:56 if-then-else.sh
-rw-rw-r-- 1 reader reader 535 Sep 30 19:44 if-then-exit-rc-improved.sh
-rw-rw-r-- 1 reader reader 556 Sep 30 19:18 if-then-exit-rc.sh
-rw-rw-r-- 1 reader reader 416 Sep 30 18:51 if-then-exit.sh

In the scripts directory for the previous chapter, we first run a normal ls -l. As you know, this prints all files in the directory. Now, if we use ls -l *, we get the exact same result. It would seem that, given an absence of arguments, ls will inject a wildcard glob for us.

Next, we use the alternative mode of ls, which is where we present a filename as the argument. In this case, because filenames are unique for each directory, we only see a single line returned.

But, what if we wanted all scripts (ending in .sh) that start with if-? We use the globbing pattern of if-*.sh. In this pattern, the * wildcard is expanded to match, as man glob says, any string, including the empty string.