Beginners Guide for File Command on Linux

The file command in Linux is used to determine the MIME encoding (e.g. “image/jpeg; charset=binary”) or file type (e.g. “ASCII text”) for the target file.

Tutorial Details

The result (stdout data) comes from the three sets of tests as follows:

• The filesystem test is used to determine the type of the file or whether the file is empty using the stat command result.
• Than magic test is performed to check the file for data in particular fixed formats.
• Lastly, the language test is used to search for particular strings that can appear anywhere in the first few blocks of a file.

Syntax of the File Command

The file command requires two arguments: one is the option, and the other is the filename.

$ file [OPTION] [FILENAME]

Find the Type of the File

The following command will return the property or description of the referenced file (it will also work for files without extensions).

$ file file.txt

Output:

Printing only the File Type

From the above command, you can remove “file.txt:” from the output by just printing the “ASCII text” in brief mode using the “-b” flag.

$ file -b file.txt 

Output:

Printing the Type of Multiple Files

You can pass multiple files as an argument to the file command to print their properties.

$ file file.txt file.zip 

Output:

Listing the Files Type in the Current Working Directory

Replace “file.txt” with a “*” wildcard to print the property for all files and directories in the current working directory.

$ file *

Output:

Listing the Files Type for the Target Directory

Following the previous command, you can specify the directory path and use the “*” wildcard to list all the file properties in the target directory.

$ file Documents/*

Output:

Listing the Files Type for Specific Range

Specify the range of files within the square bracket “[RANGE]” to find the file property.

$ file [a-z]*

Output:

Align the Output

As you can see above, the padding makes the command unaligned, which can be aligned using the “-N” flag.

$ file -N [a-z]*

Output:

Look Inside the Compressed File

The following command will look into the compressed “.zip” or “.tar.xz” files and determine the file property inside.

$ file -z file.zip 
$ file -z file.tar.xz 

Output:

Reading the Special Files

The “-s” flag allows you to read special files like “/dev/sda” or “/dev/null” files, as shown.

$ sudo file -s /dev/sda
$ file -s /dev/null

Output:

Reading the File MIME Encoding

The “-i” flag can be used to determine the MIME encoding for the target file.

$ file -i file.tar.xz 
$ file -i file.txt
$ file -i photo.jpg 

Output:

That was the end of the final example.

Bye bye! We’ll talk again in the next article.