The asterisk, also known as a wildcard, when used in a file name expansion, matches all the file names in a directory. The file name expansion is also known as Globbing. It takes into account some special characters as *, which is expanded to all, and ?, which expands to any single character along with some character lists in brackets:
zarrelli:~$ ls -lah [es]*
-rw-r--r-- 1 zarrelli zarrelli 36 Feb 17 07:50 external-data
-rwxr--r-- 1 zarrelli zarrelli 211 Feb 17 17:40 external-script-return.sh
-rwxr--r-- 1 zarrelli zarrelli 373 Feb 18 11:58 external-script-return-whatever.sh
-rwxr--r-- 1 zarrelli zarrelli 257 Feb 17 08:22 external-script.sh
-rwxr--r-- 1 zarrelli zarrelli 391 Feb 17 17:37 sourcing-return.sh
-rwxr--r-- 1 zarrelli zarrelli 235 Feb 19 10:40 sourcing-return-whatever.sh
-rwxr--r-- 1 zarrelli zarrelli 284 Feb 17 07:53 sourcing.sh
As we can see in the example, we listed all the * files whose names started either with e or s. But it also interprets the ^ character as negation:
zarrelli@moveaway:~/Documents/My books/Mastering bash/Chapter 4/Scripts$ ls -lah [^es]*
-rw-r--r-- 1 zarrelli zarrelli 0 Feb 16 08:35 *
-rw-r--r-- 1 zarrelli zarrelli 0 Feb 16 08:35 1
-rw-r--r-- 1 zarrelli zarrelli 0 Feb 16 08:35 2
-rw-r--r-- 1 zarrelli zarrelli 0 Feb 16 08:35 3
-rwxr--r-- 1 zarrelli zarrelli 249 Feb 16 13:24 comment.sh
-rwxr-xr-x 1 zarrelli zarrelli 409 Feb 16 14:59 menu.sh
-rwxr--r-- 1 zarrelli zarrelli 700 Feb 19 11:22 parm-sub.sh
-rw-r--r-- 1 zarrelli zarrelli 0 Feb 19 14:16 test.colon
-rw-r--r-- 1 zarrelli zarrelli 10 Feb 19 14:22 test.colon.2
-rw-r--r-- 1 zarrelli zarrelli 5 Feb 16 14:07 test.txt
-rwxr-xr-x 1 zarrelli zarrelli 42 Feb 19 14:14 test-variable.sh
In this case, we listed all the files in the current directory whose names did not start with either e or s. Be careful as the * in file globbing does not trap file names starting with a dot:
zarrelli:~$ mkdir test
zarrelli:~$ cd test/
zarrelli:~$ touch file
zarrelli:~$ touch .another_file
zarrelli:~$ ls -l *
-rw-r--r-- 1 zarrelli zarrelli 0 Feb 19 15:08 file
Something is clearly missing, so let's try this:
zarrelli:~$ ls -lah
total 8.0K
drwxr-xr-x 2 zarrelli zarrelli 4.0K Feb 19 15:08 .
drwxr-xr-x 3 zarrelli zarrelli 4.0K Feb 19 15:08 ..
-rw-r--r-- 1 zarrelli zarrelli 0 Feb 19 15:08 .another_file
-rw-r--r-- 1 zarrelli zarrelli 0 Feb 19 15:08 file
You could also try this for some nice effects:
ls -l .*
Final remarks, you will find the asterisk used as a wild card in regular expressions as well with the same meaning and also as a multiplication operator in arithmetic operations.