Asterisk
The asterisk (*- also called "splat" or "star") is
a substitution symbol that represents zero or more characters, except
the leading dot on a hidden file. The asterisk is often referred to as
a wildcard character. The asterisk can be very helpful with many
commands such as the ls
(list), cp
(copy), rm
(remove) and mv
(move). If there were a large number of files in a directory and you
only wanted to get a listing of project files that started with p1, you
could use an example like the one shown in Figure .
If you enter the ls
command by itself, you will see all files in the current
directory.
If you enter ls
d*, you will see all files that
start with the letter d plus all directories that start with d,
followed by a colon, then the directory contents.
Question Mark
The question mark (?) is a substitution character that matches any
single character, except for the leading dot on a hidden file. The
question mark is also referred to as a wildcard character. Figure
shows an example of the ls
command using the question mark in the fourth position. This indicates
that the file or directory name must start with dir but any character
can be in the fourth position and the file name cannot be more than
four characters long.
If no file name matches the wildcard
character (whether * or ?), you will receive the following error
message:
$ ls z?
z?: No such file or directory
$
Square Brackets
Square brackets ([ ]) can be used to match a set or range of
characters for a single character position in the file or directory
name. The characters inside the brackets do not generally need to be
in any order; for example, [abc] is the same as [cab]. However, if you
are looking for a range of characters, they must be in proper order
(for example, [a-z] or [3-9]). If you want to search for all
alphabetic characters, whether lowercase or uppercase, use [A-z] for
the pattern to match. You can use alphabetic or numeric characters for
the search pattern.
Figure
shows two examples using square brackets along with the asterisk
wildcard character. The first example defines a range and will list
all files and directories that start with the lower case letters b
through f with anything after that. The second example specifies that
the first character must be either the letter a or f and anything can
be after that. Notice that only files starting with f are displayed in
example 2.
Semicolon
The semicolon (;) enables you to enter multiple commands on a single
command line before pressing enter. Entering multiple commands on one
command line is an efficient way to accomplish a task. The semicolon
is also referred to as the command separator. Figure
shows two examples using the semicolon to separate commands. In the
first example, the clear
command will clear the screen, the cd
command will return you to your home directory and the ls
command will list files in that directory. The second example displays
the current date and time, and then the calendar for the current
month.
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Interactive
Media Activity
(Flash,
95 kB) |
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Using
Metacharacters
In this media activity,
you are logged in as user2 and your current working directory is: /home/user2. Refer to the Class File Tree Structure by clicking the 'tree' button located on the Menu Bar and type the commands that would accomplish the requested objectives.
Note: Be sure to press enter after each one. Click on step 1 to begin.
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Lab
Activity
(Adobe Acrobat
Reader, 44 kB) |
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Directory Listings with Metacharacters
In this lab
you will work with various metacharacters and use them with
the ls command to refine your directory listings. |
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