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Options And Arguments
This brings us to a very important point about how most commands work. Commands are often followed by one or more options that modify their behavior, and further, by one or more arguments, the items upon which the command acts. So most commands look kind of like this:
command -options arguments
command -options arguments
Most commands use options consisting of a single character preceded by a dash, for ex- ample, “-l”, but many commands, including those from the GNU Project, also support long options, consisting of a word preceded by two dashes. Also, many commands allow multiple short options to be strung together. In this example, the ls command is given two options, the “l” option to produce long format output, and the “t” option to sort the result by the file's modification time.
[me@linuxbox ~]$ ls -lt
[me@linuxbox ~]$ ls -lt
More Fun With ls
We'll add the long option “--reverse” to reverse the order of the sort:
[me@linuxbox ~]$ ls -lt --reverse
[me@linuxbox ~]$ ls -lt --reverse
Note that command options, like filenames in Linux, are case-sensitive.
The ls command has a large number of possible options. The most common are listed in Table 3-1.
Table 3- 1: Common ls Options
Option | Long Option | Description |
-a | --all | List all files, even those with names that begin |
with a period, which are normally not listed | ||
(i.e., hidden). | ||
-A | --almost-all | Like the -a option above except it does not |
list . (current directory) and .. (parent | ||
directory). | ||
-d | --directory | Ordinarily, if a directory is specified, ls will |
list the contents of the directory, not the | ||
directory itself. Use this option in conjunction | ||
with the -l option to see details about the | ||
directory rather than its contents. | ||
-F | --classify | This option will append an indicator character |
to the end of each listed name. For example, a | ||
“/” if the name is a directory. | ||
-h | --human-readable | In long format listings, display file sizes in |
human readable format rather than in bytes. | ||
-l | Display results in long format. | |
-r | --reverse | Display the results in reverse order. Normally, |
ls displays its results in ascending | ||
alphabetical order. | ||
-S | Sort results by file size. | |
-t | Sort by modification time. |