ls

Description

ls is a standard Unix utility that lists the files in the directory specified in the path. By default it lists the files in the current directory. It is similar to dir command in Windows.

It can be modified with flags to further improve its functionality.

The command syntax is:

ls [flags] [path to directory]

Flags

Some of the popular flags that are used with ls command are as follows:

• -a or --all: lists hidden items
• -l: display more information about the items.
• -r: lists the items in reverse order.
• -t: lists the item sorted by time.
• --help: get more information about the command and uncommon flags.

-a

Description:

With the -a option, the ls command will show hidden files and sub-folders. By default, files and folders beginning with . are hidden and they are not listed when doing a typical ls command

Usage: Consider we are inside a folder that contains three files: file1.txt, file2.txt and a hidden file .file.txt. If we want to see the hidden file we need to use the -a flag as:

ls -a

Output:

.file.txt  file1.txt  file2.txt

-l

Description:

With the -l flag, the ls command will list the files in the current directory in a detailed, long-form format.

The long form listing consists of the following columns.

1. File Type and Permissions: The leftmost column displays a series of characters that indicate the file type and its permissions. The first character indicates the file type, with '-' for a regular file, 'd' for a directory, 'l' for a symbolic link, and more. The following nine characters represent the file's permissions, with 'r' for read, 'w' for write, and 'x' for execute. These characters are displayed for the file owner, the group, and others, with three characters for each.

2. Number of Hard Links: The second column shows the number of hard links associated with the file or directory. Hard links are multiple directory entries that point to the same inode on disk.

3. Owner: The third column displays the owner of the file or directory.

4. Group: The fourth column shows the group associated with the file or directory.

5. File Size: The fifth column indicates the size of the file in bytes.

6. Modification Date and Time: The next columns display the date and time when the file was last modified.

7. File/Directory Name: The final column shows the name of the file or directory.

Usage: Taking the example from above we can enter the following into the terminal

ls -l

Output:

-rw-r--r-- 1 username groupname 1024 Nov  5 12:40 file1.txt
-rw-r--r-- 1 username groupname 1024 Nov  5 12:40 file2.txt

Let's interpret the first line of output to better understand the flag.

• -rw-r--r--: This represents the file permissions and file type. It indicates that file1.txt is a regular file (- indicates a regular file, d would indicate a directory). The rw-r--r-- part represents the permissions for the file (read, write for the owner, read for the group, and read for others).

• 1: This shows the number of hard links to the file or directory. In this case, it's 1.

• username: This is the owner of the file.

• groupname: This is the group associated with the file.

• 1024: This is the file size in bytes.

• Nov 5 12:40: These are the date and time of last modification.

• file1.txt: This is the name of the file.

-r

Description:

With the -a option, the ls command will show files and sub-folders sorted in reverse alphanumeric order.

Usage: Taking the example from above we can enter the following into the terminal

ls -r

Output:

file2.txt  file1.txt

-t

Description:

With the -t option, the ls command will show files and sub-folders sorted by time.

Usage: Taking the example from above we can enter the following into the terminal

ls -t

Output:

file2.txt  file1.txt

--help

Description:

With the --help option, the ls command will show other flags and options for the command that are not commonly used.

Usage:

ls --help

Examples

1. When you want to long list all files (Including Hidden Files) in your home directory:

   ls -la ~
   

   which is shorthand notation for chaining flags, and is equivalent to:

      ls -l -a ~
   

   More about this in the Additional Information section.

2. If you want to know the items contained in /etc folder of the filesystem:

   ls /etc or ls [path_to_etc]
   

3. If you want to sort the content in your home directory to see which was added most recently:

    ls -t ~
   

4. If you want to look at the items in a folder in reverse alphabetical order:

    ls -r [path_to_folder]
   

Additional Information

As seen in example 1, the flags can be combined. This is common for all commands in linux that do not take a parameter after the flag. Hence the -l and -a flag can be combined to -la flag.

Exercises

1. Use the --help flag and find the flag to recursively list the items in a folder.

2. Navigate to the /usr/bin directory and find out the tools installed in your system.

3. Find the number of pictures in your system. Hint: wc command prints the number of newline, words and bytes for each file.

4. Navigate to your Downloads folder and find out what was your first download.

5. Reverse list the items in your home directory.