Linux fmt Command with Practical Examples

Introduction

In this lab, you will learn how to use the Linux fmt command to format text files. The fmt command is a powerful tool for adjusting the width and alignment of text, allowing you to reformat text files, remove extra whitespace, and align text consistently. You will start by understanding the purpose of the fmt command, then explore how to format text files using various options, and finally customize the command to suit your specific needs.

The lab covers the following steps:

1. Understand the Purpose of the fmt Command
2. Format Text Files with the fmt Command
3. Customize fmt Command Options

The fmt command is a standard tool in Linux and is typically pre-installed. No additional installation is required.

Linux Commands Cheat Sheet

Understand the Purpose of the fmt Command

In this step, you will learn about the purpose and usage of the fmt command in Linux. The fmt command is a powerful tool for formatting text files, allowing you to adjust the width and alignment of text.

The fmt command is commonly used to:

• Reformat text files to a specified width
• Remove extra whitespace and line breaks
• Align text in a consistent manner

Let's start by creating a sample text file that we'll use throughout this lab:

echo "This is a sample text file with some long lines that need to be formatted." > sample.txt

Example output:

This is a sample text file with some long lines that need to be formatted.

Now, let's use the fmt command to format the text file:

fmt sample.txt

Example output:

This is a sample text file with some long lines
that need to be formatted.

As you can see, the fmt command has automatically reformatted the text to fit within the default line width of 75 characters.

Format Text Files with the fmt Command

In this step, you will learn how to use the fmt command to format text files with various options.

First, let's create another sample text file with some longer lines:

echo "This is another sample text file with some very long lines that need to be reformatted to a specific width." > sample2.txt

Example output:

This is another sample text file with some very long lines that need to be reformatted to a specific width.

Now, let's use the fmt command to format the text file to a specific width of 60 characters:

fmt -w 60 sample2.txt

Example output:

This is another sample text file with some very
long lines that need to be reformatted to a
specific width.

The -w option specifies the desired width for the reformatted text. You can adjust this value to suit your needs.

Another useful option is -c, which centers the text:

fmt -w 60 -c sample2.txt

Example output:

   This is another sample text file with some very
   long lines that need to be reformatted to a
   specific width.

The fmt command also supports other options, such as -u to remove unnecessary whitespace and -s to preserve the spacing between words.

Customize fmt Command Options

In this final step, you will learn how to customize the fmt command with additional options to suit your specific text formatting needs.

One common use case is to preserve the original indentation of the text. Let's create a sample file with indented lines:

cat > sample3.txt << EOF
    This is a sample text file with
        indented lines that need to be
            preserved.
EOF

Example output:

    This is a sample text file with
        indented lines that need to be
            preserved.

To preserve the indentation, we can use the -p option:

fmt -p sample3.txt

Example output:

    This is a sample text file with
        indented lines that need to be
            preserved.

As you can see, the indentation has been preserved.

Another useful option is -t, which can be used to specify the tab size. Let's create a sample file with tabs:

cat > sample4.txt << EOF
This	is a sample text file	with tabs.
EOF

Example output:

This	is a sample text file	with tabs.

Now, let's format the file using the -t option to set the tab size to 4 spaces:

fmt -t 4 sample4.txt

Example output:

This    is a sample text file    with tabs.

The fmt command provides several other options, such as -s to preserve spacing between words, -u to remove unnecessary whitespace, and -w to set the desired line width. Experiment with these options to find the best configuration for your text formatting needs.

Summary

In this lab, you learned about the purpose and usage of the fmt command in Linux, which is a powerful tool for formatting text files. You started by creating a sample text file and using the fmt command to automatically reformat the text to fit within the default line width. Then, you learned how to use various options with the fmt command, such as specifying a custom line width and centering the text, to format the text files according to your needs.

The fmt command is commonly used to reformat text files, remove extra whitespace and line breaks, and align text in a consistent manner. By understanding the capabilities of the fmt command, you can efficiently format and organize your text-based documents.

Linux Commands Cheat Sheet