Working with Wildcards

Shells support a rich set of wildcards to help work with files. Awildcard is an expression that the shell uses to expand to a number of file names&mdashthat is, to all files that match the expression. Wildcards are often called globs. The use of globs is called globbing.

The * Wildcard

The main wildcard is a star, or asterisk (*), character. (Java programmers sometimes call this a splat.) A star alone matches anything and nothing, sort of Zen-like. Typically, you need to pair a star with some other characters to form a more specific expression. For example, *.txt matches all file names ending with .txt, including all of the following:

.txt

a.txt

a_very_long_name.txt

A_FILE_NAME_WITH_UPPERCASE_LETTERS.txt

The * means that you don&rsquot care what letters there are before the .txt.

Typically, an expression such as *.txt will match all text files. You can refine the wildcard expression further. For example, a*.txt matches all file names that start with a lowercase letter a and end with .txt. Again, the * means you don&rsquot care about any letters in between. Using the files from the previous list, a*.txt would match just the following:

a.txt

a_very_long_name.txt
>
> If you want files that start with an uppercase A or a lowercase a and end with .txt, use the expression [Aa]*.txt. This expression would match the following files:

a.txt

a_very_long_name.txt

A_FILE_NAME_WITH_UPPERCASE_LETTERS.txt

You can use the star more than once&mdashfor example, with the expression a*v*.txt. This expression would match only one file in the example list of files:

a_very_long_name.txt

On MS-DOS, each program has to support wildcards on its own. A few DOS commands, such as DIR, support a limited number of wildcard expressions. This is very different with Unix and Linux, as the shell supports the wildcard expressions so each program doesn&rsquot have to.