Linux file Command with Practical Examples

Introduction

In this lab, we will explore the Linux file command and learn how to identify different types of files, including text files, binary files, and compressed files. We will start by using the file command to determine the type of various files, and then move on to handling compressed files.

The file command is a versatile tool that can be used to identify the type of a file based on its contents, even if the file extension doesn't match the actual file type. This can be particularly useful when dealing with unknown or unusual file types.

Linux Commands Cheat Sheet

Exploring the file Command

In this step, we will explore the versatile file command in Linux. The file command is used to determine the type of a file, whether it is a text file, an executable, or a binary file.

Let's start by running the file command on a few different files:

cd ~/project
file README.md
file Dockerfile
file example.zip

Example output:

README.md: Markdown document, UTF-8 text
Dockerfile: ASCII text
example.zip: Zip archive data, at least v2.0 to extract

As you can see, the file command provides information about the type of each file. For the README.md file, it identifies it as a Markdown document. For the Dockerfile, it recognizes it as an ASCII text file. And for the example.zip file, it identifies it as a Zip archive.

The file command can also be used to identify the type of a file based on its contents, even if the file extension doesn't match the actual file type. Let's try an example:

echo "This is a text file" > example.txt
file example.txt

Example output:

example.txt: ASCII text

Even though the file extension is .txt, the file command correctly identifies it as an ASCII text file.

The file command is a powerful tool for understanding the contents of files on your system. It can be particularly useful when dealing with unknown or unusual file types.

Identifying File Types

In this step, we will learn how to use the file command to identify different types of files, including text files, binary files, and compressed files.

Let's start by creating some sample files:

cd ~/project
echo "This is a text file" > text_file.txt
dd if=/dev/urandom of=binary_file.bin bs=1M count=1 > /dev/null 2>&1
gzip text_file.txt

Now, let's use the file command to identify the file types:

file text_file.txt
file binary_file.bin
file text_file.txt.gz

Example output:

text_file.txt: ASCII text
binary_file.bin: data
text_file.txt.gz: gzip compressed data, was "text_file.txt", last modified: Tue Apr 18 12:34:56 2023, max compression

As you can see, the file command correctly identifies the text_file.txt as an ASCII text file, the binary_file.bin as a binary data file, and the text_file.txt.gz as a gzipped file.

The file command can also provide more detailed information about the contents of a file. For example, let's try it on a compressed file:

file -z text_file.txt.gz

Example output:

text_file.txt.gz: gzip compressed data, was "text_file.txt", last modified: Tue Apr 18 12:34:56 2023, max compression

The -z option tells the file command to look inside compressed files and provide information about the original file.

Understanding how to use the file command to identify different file types is an essential skill for working with files in a Linux environment.

Handling Compressed Files

In this step, we will learn how to work with compressed files using the file command and other Linux utilities.

First, let's create a compressed file:

cd ~/project
tar -czf archive.tar.gz text_file.txt binary_file.bin

Now, let's use the file command to identify the compressed file:

file archive.tar.gz

Example output:

archive.tar.gz: gzip compressed data, last modified: Tue Apr 18 12:34:56 2023, max compression

The file command correctly identifies the archive.tar.gz file as a gzipped compressed file.

To extract the contents of the compressed file, we can use the tar command:

tar -xzf archive.tar.gz
ls -l

Example output:

total 2048
-rw-r--r-- 1 labex labex     20 Apr 18 12:34 binary_file.bin
-rw-r--r-- 1 labex labex     19 Apr 18 12:34 text_file.txt

The tar -xzf command extracts the contents of the archive.tar.gz file, and we can see the extracted binary_file.bin and text_file.txt files.

Linux also provides other tools for working with compressed files, such as gzip and gunzip for handling gzipped files, and unzip for handling ZIP archives. Let's try using gunzip to decompress the text_file.txt.gz file we created earlier:

gunzip text_file.txt.gz
file text_file.txt

Example output:

text_file.txt: ASCII text

The gunzip command decompresses the text_file.txt.gz file, and the file command confirms that the decompressed file is an ASCII text file.

Understanding how to work with compressed files is an essential skill for managing files and data in a Linux environment.

Summary

In this lab, we explored the versatile file command in Linux, which is used to determine the type of a file. We learned how to use the file command to identify different file types, including text files, binary files, and compressed files. The file command can provide valuable information about the contents of a file, even if the file extension doesn't match the actual file type. We also practiced creating sample files and using the file command to analyze their types. This lab has equipped us with a better understanding of the file command and its practical applications in working with various file types on a Linux system.

Linux Commands Cheat Sheet