fmt

Understanding the Basics of fmt

At its core, fmt reformats text by wrapping lines to a specified width. If no width is specified, it defaults to 79 characters. This is incredibly handy for preparing text for email, documents, or simply improving the readability of long, unbroken lines in a file.

Basic Usage:

The simplest way to use fmt is to pipe text to it:

cat my_long_text_file.txt | fmt

This command reads my_long_text_file.txt, and fmt reformats the text, wrapping lines at the default 79-character width, before printing to the standard output. To send the output to a new file:

cat my_long_text_file.txt | fmt > formatted_text.txt

Customizing fmt’s Behavior

fmt offers many options to fine-tune its output:

Specifying Width:

You can change the wrapping width using the -w option:

cat my_long_text_file.txt | fmt -w 80

This sets the wrapping width to 80 characters.

Suppressing Leading Whitespace:

Often, text files contain inconsistent indentation. The -u option removes leading whitespace from each line before reformatting:

cat my_unformatted_file.txt | fmt -u

Maintaining Paragraph Separation:

fmt cleverly handles paragraph separation. Blank lines are preserved, ensuring paragraphs remain distinct even after reformatting:

cat my_file.txt | fmt

(Assuming my_file.txt contains paragraphs separated by blank lines).

Handling Tab Characters:

Tabs can disrupt consistent formatting. fmt handles tabs by interpreting them based on the TABSTOP environment variable, usually set to 8 characters.

Dealing with Extremely Long Lines:

Very long lines might not wrap correctly. The -p option helps to preserve lines that exceed the specified width:

cat my_file.txt | fmt -w 60 -p

This command attempts to keep lines under 60 characters but allows lines exceeding this length to remain intact.

Input from a file directly:

You don’t always need to use cat. fmt can accept filenames as arguments:

fmt -w 60 my_file.txt

This reformats my_file.txt directly, wrapping lines to a width of 60 characters.

Advanced Examples: Combining Options

fmt’s true power lies in combining its options. For instance, to remove leading whitespace and set a custom width:

fmt -u -w 50 my_file.txt > output.txt

This command reformats my_file.txt, removing leading whitespace and setting the wrapping width to 50 characters. The output is saved to output.txt.

Beyond Simple Formatting: Practical Applications

fmt shines in automating text cleanup tasks within shell scripts or as part of a larger data processing pipeline. Imagine using fmt to standardize the format of log files before analysis, or to prepare text for inclusion in a generated report. Its simple yet effective approach to text manipulation makes it a tool in a Linux user’s arsenal.