Often you want a command to work with a group of files. Wildcards are
used to create a filename expansion pattern: a series of characters
and wildcards that expands to a list of filenames. For example, the pattern
/etc/* expands to a list of all6.2 the files in /etc.
* is a wildcard that can stand for any series of characters, so the
pattern /etc/* will expand to a list of all the filenames beginning
This filename list is most useful as a set of arguments for a command. For example,
the /etc directory contains a series of subdirectories called rc0.d,
rc1.d, etc. Normally to view the contents of these, you would type
ls /etc/rc0.d /etc/rc1.d /etc/rc2.d /etc/rc3.d
ls /etc/rc4.d /etc/rc5.d /etc/rc6.d /etc/rcS.d
This is tedious. Instead, you can use the ? wildcard as shown here:
/etc/rc?.d expands to a list of filenames that begin with rc,
followed by any single character, followed by .d.
Available wildcards include the following:
Matches any group of 0 or more characters.
Matches exactly one character.
If you enclose some characters in brackets, the result is a wildcard
that matches those characters. For example, [abc] matches either
a, or b, or c. If you add a ^ after the first bracket, the sense
is reversed; so [^abc] matches any character that is not a,
b, or c. You can include a range, such as [a-j], which matches
anything between a and j. The match is case sensitive, so to allow any letter,
you must use [a-zA-Z].
Expansion patterns are simple once you see some concrete examples:
This will give you a list of all filenames that end in .txt,
since the * matches anything at all.
This gives a list of filenames that end in either .h
This gives you all three-letter filenames that begin with a.
This gives you all three-letter filenames that do not
begin with a.
This gives you every filename that starts with a, regardless
of how many letters it has.