The is command, like in, is one of those you expect to be very straightforward. It lists files, but how many options can it possibly have? In true Linux style, the answer is many, although again you need only know a few to wield great power!
The basic usage is simply is, which out the files and directories in the current location. You can filter that using normal wildcards, so all these are valid:
Any directories that match these filters are recursed into one level. That is, if you run is my* and you have the files myfiie1.txt and myfiie2.txt and a directory mystuff, the matching files are printed first. Then is prints the contents of the mystuff directory.
The most popular parameters for customizing the output of is are
• -r Recursively lists directories.
All files that start with a period are hidden in Linux, so that includes the .gnome directory in your home directory, as well as .bash_history and the . and .. implicit directories that signify the current directory and the parent. By default, is does not show these files, but if you run is -a, they are shown. You can also use ls -a to show all the hidden files except . and ... The -h parameter needs to be combined with the -s parameter, like this:
That outputs the size of each matching file in a human-readable format, such as 108KB or 4.5MB.
Using the -l parameter enables much more information about your files. Instead of just providing the names of the files, you get output like this:
drwxrwxr-x 24 paul paul 4096 Dec 24 21:33 arch
-rw-r—r— 1 paul paul 18691 Dec 24 21:34 COPYING
-rw-r—r— 1 paul paul 88167 Dec 24 21:35 CREDITS
drwxrwxr-x 2 paul paul 4096 Dec 24 21:35 crypto
That shows four matches and prints a lot of information about each of them. The first row shows the arch directory; you can tell it is a directory because its file attributes starts with a d. The rwxrwxr-x following that shows the access permissions, and this has special meanings because it is a directory. Read access for a directory allows users to see the directory contents, write access allows you to create files and subdirectories, and execute access allows you to cd into the directory. If a user has execute access but not read access, he will be able to cd into the directory but not list files.
Moving on, the next number on the line is 24, which also has a special meaning for directories: It is the number of subdirectories, including . and ... After that is paul paul, which is the name of the user owner and the group owner for the directory. Next is the size and modification time, and finally the directory name itself.
The next line shows the file copying, and most of the numbers have the same meaning, with the exception of the 1 immediately after the access permissions. For directories, this is the number of subdirectories, but for files this is the number of hard links to this file. A 1 in this column means this is the only filename pointing to this inode, so if you delete it, it is gone.
Ubuntu comes configured with a shortcut command for ls -l: ll.
The --sort parameter allows you to reorder the output from the default alphabetical sorting. You can sort by various things, although the most popular are extension (alphabetically), size (largest first), and time (newest first). To flip the sorting (making size sort by smallest first), use the -r parameter also. So, this command lists all .ogg files, sorted smallest to largest:
Finally, the -r parameter recurses through subdirectories. For example, typing ls /etc lists all the files and subdirectories in /etc, but ls -r /etc lists all the files in and subdirectories in /etc, all the files and subdirectories in /etc/acpi, all the files and subdirectories in /etc/acpi/actions, and so on until every subdirectory has been listed.
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