mread Command in Linux

Introduction to the Linux mread Command

In this tutorial, we will delve into the Linux mread command, a powerful utility designed for extracting data from files. The mread command empowers users to read a precise number of bytes from a given file and then present the resulting data. We will cover the fundamental syntax of the mread command, examine its diverse set of options, and demonstrate real-world file reading scenarios through practical examples.

This lab explores the following core areas:

  1. Grasping the Fundamentals of the mread command
  2. Investigating the Options Available in the mread command
  3. Implementing File Reading Operations with mread

Understanding the mread Command

In this segment, we will familiarize ourselves with the mread command, a crucial Linux tool for reading data from files. Specifically, the mread command provides the functionality to read a determined quantity of bytes from a file and then output that information.

To properly understand the mread command, let's execute the command below:

mread -h

Example output:

Usage: mread [OPTION]... FILE
Read FILE, writing to standard output.

With no FILE, or when FILE is -, read standard input.

Mandatory arguments to long options are mandatory for short options too.
  -n, --bytes=BYTES        print BYTES bytes
  -c, --chars=CHARS        print CHARS characters
  -s, --skip-bytes=BYTES   skip BYTES input bytes first
  -q, --quiet, --silent    never output headers giving file names
  --help     display this help and exit
  --version  output version information and exit

The mread command features a collection of options to precisely define how the file reading process is performed. Let's examine the most frequently used options:

  1. -n, --bytes=BYTES: This option specifies the exact number of bytes that the command will read from the specified file.
  2. -c, --chars=CHARS: This option defines the exact number of characters to be read from the file.
  3. -s, --skip-bytes=BYTES: This option allows you to skip a defined number of bytes at the beginning of the file before the reading operation starts.
  4. -q, --quiet, --silent: This option removes the display of the file name header in the output. This is useful for scripting and automation.

Now that we have a fundamental grasp of the mread command, let's proceed to explore its practical applications and options with further examples.

Exploring mread Command Options

In this section, we'll dive into the various options available with the mread command. We will demonstrate how these options provide versatile methods for reading files, tailored to specific requirements.

Let's begin by creating a sample file for our tests:

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

Now, let's put some of the mread command options to the test:

  1. Reading a Specific Number of Bytes:

    mread -n 10 sample.txt

    Example output:

    This is a

    As demonstrated, the -n option controls the precise number of bytes that are read from the input file.

  2. Reading a Specific Number of Characters:

    mread -c 10 sample.txt

    Example output:

    This is a

    The -c option lets you define the exact number of characters to be extracted from the file.

  3. Skipping Bytes Before Reading:

    mread -s 5 -n 10 sample.txt

    Example output:

    a sample

    The -s option allows you to jump over a specified number of bytes before the command starts reading, effectively selecting a section of the file.

  4. Reading from Standard Input:

    echo "This is another sample text." | mread -c 10

    Example output:

    This is an

    If the FILE argument is omitted or set to -, mread will take its input from standard input, enabling piping from other commands.

  5. Suppressing the File Name Header:

    mread -q -n 10 sample.txt

    Example output:

    This is a

    The -q (or --quiet) option turns off the display of the file name in the output, making the output cleaner for parsing or other uses.

By understanding these options, you can effectively tailor the mread command to your specific requirements, allowing for precise and flexible file reading.

Performing File Reading Operations with mread

In this final section, we will apply the mread command to execute practical file reading operations.

Firstly, we create a larger sample file:

dd if=/dev/urandom of=sample.bin bs=1M count=5

This will generate a 5 MB binary file containing random data.

Now, let's perform file reading with mread:

  1. Reading the First 1 MB of the File:

    mread -n $((1024*1024)) sample.bin

    This command reads and outputs the initial 1 MB of the sample file.

  2. Reading the Last 1 MB of the File:

    mread -s $((5*1024*1024-1024*1024)) -n $((1024*1024)) sample.bin

    Here, we skip the first 4 MB of the file and read the final 1 MB.

  3. Reading the File in 512 KB Chunks:

    chunk_size=$((512*1024))
offset=0
while [ $offset -lt $((5*1024*1024)) ]; do
  mread -s $offset -n $chunk_size sample.bin
  offset=$((offset + chunk_size))
done

    This example breaks down the file into 512 KB segments and displays them sequentially.

  4. Comparing File Contents with Another File:

    mread sample.bin | diff - reference.bin

    Assuming a reference.bin file is available, this command compares the content of sample.bin with reference.bin, displaying differences.

By reviewing these examples, you should now be well-versed in using the mread command to read files using different techniques.

Conclusion

In this lab, we learned how to use the Linux mread command for reading data from files within a systemadmin context. We examined the different options available with the mread command, for example, reading a specific amount of bytes or characters, or skipping bytes prior to reading. We explored many different examples of how to use the mread command in order to read files. We focused on learning the most important information on how to use the mread command and its options, and how to effectively use it to read files as a systemadmin or Linux user.

400+ Linux Commands