• * : Matches any string
• *a* : Matches any string containing an ‘a’
• *9* : Matches any string containing a digit ‘9’
• *.[xy] : Matches any string ending with .x or .y
• *[ab]* : Matches any string containing a character ‘a’ or ‘b’
• *[42]* : Matches any string containing a digit ‘4’ or ‘2’
• ? : Matches any single character

Examples

Let us consider the following files:
$ ls -l
Sample outputs:

total 0
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:37 001
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:37 002
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:39 1.txt
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:37 13
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:37 13aa
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:37 42
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:37 4213aa
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:42 A.txt
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:22 bar
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:39 c.txt
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:37 cd4213aa
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:37 file2.txt
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:37 file4.txt
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:37 file40.txt
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:22 foo
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:22 raj
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:22 sai
-rw-r--r--  1 veryv  wheel  0 Aug 24 01:22 vivek

To list all .txt file run:
$ ls *.txt
1.txt c.txt file2.txt file4.txt file40.txt
To see txt files with 1 char names (eg z.txt, 3.txt)
$ ls ?.txt
1.txt c.txt
List txt files that start with a capital letter:
$ ls [A-Z]*.txt
A.txt
Can you guess what the following command does?
$ ls [A-Za-z]*.txt
A.txt c.txt file2.txt file4.txt file40.txt
You can use a wildcard with any Linux/Unix command such as rm command,cp command,mv command,tar command and so on. To delete files containing a number ‘4’ or ‘2’ in their filename:
$ ls *[42]*
$ rm -v *[42]*
To limit to .jpg extension:
$ ls *[42]*.jpg
$ rm -v *[42]*.jpg
Another example where file name start with a capital ‘X’ and ends with .JPG extension and files containing a number ‘4’ or ‘2’ in their filename:
$ ls X*[42]*.jpg
$ rm -v X*[42]*.jpg

A note about option which change globbing behavior for bash shell

Turn on extglob by running the following shopt command:
$ shopt -s extglob
From the bash man page:

Composite patterns may be formed using one or more of the following sub-patterns:
 
      ?(pattern-list)
               Matches zero or one occurrence of the given patterns
      *(pattern-list)
               Matches zero or more occurrences of the given patterns
      +(pattern-list)
               Matches one or more occurrences of the given patterns
       @(pattern-list)
               Matches one of the given patterns
       !(pattern-list)
               Matches anything except one of the given patterns

To see all the mp4 and mov files that start with either “foo” or “bar”:
$ ls +(foo|bar)*+(.mp4|.mov)
To list all the files except ones matching *.mp4:
$ ls -l !(*.mp4)
OR delete all the files except ones matching *.gif files:
$ rm -v !(*.gif)
For more info see your shell man page:
$ man bash
$ man ksh