How to Use the Command `fold` (with examples)

The fold command in Unix-like operating systems is a text processing utility designed to wrap each line in an input file to fit a specified width. By default, it formats the text to wrap at 80 characters. This command is particularly useful for preparing text for display in environments where text wrapping is constrained by specific width requirements. For instance, it can be used within scripts to prepare documents for printing where lines need to fit within set margins. The output of the fold command is printed to standard output (stdout), making it easy to integrate with other command-line utilities.

Use case 1: Wrap each line to default width (80 characters)

Code:

fold path/to/file

Motivation:

When dealing with plain text files that need to be displayed on terminals or printed, it’s often necessary to ensure that each line does not exceed a certain width—commonly 80 characters—to maintain readability and structure. This use case is a classic default setting where 80 characters per line are the conventional maximum width in terminal displays.

Explanation:

• fold: The command that executes the folding operation, ensuring that text is wrapped correctly.
• path/to/file: Specifies the path to the file you want to wrap. This argument is essential for directing the fold command to the appropriate text file.

Example output:

If the text inside the file before folding is:

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

The output on standard output will be:

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor incididunt 
ut labore et dolore magna aliqua.

Use case 2: Wrap each line to width “30”

Code:

fold -w30 path/to/file

Motivation:

In cases where documents or data sets are packaged into small formats, such as narrow-column newspaper articles or reports formatted for physical print (like brochures), lines need to be kept shorter than the default 80 characters. This example demonstrates customizing the fold command to wrap lines to a 30-character width.

Explanation:

• fold: Initiates the command for processing the input file.
• -w30: The -w flag specifies the width, followed by 30 to indicate that each line should be wrapped at 30 characters.
• path/to/file: Points to the file containing text that needs wrapping, guiding the command where to apply the width setting.

Example output:

Initial file content:

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

Output:

Lorem ipsum dolor sit amet,
consectetur adipiscing elit. S
ed do eiusmod tempor incididu
nt ut labore et dolore magna a
liqua.

Use case 3: Wrap each line to width “5” and break the line at spaces

Code:

fold -w5 -s path/to/file

Motivation:

For preserving the integrity of words while still reducing line length, this use case shows how to use the fold command with the -s flag to break at spaces. This can be useful for formatting data outputs tight on space, such as tables or forms that require clear column division but still maintain legibility by breaking lines at space-separated word boundaries.

Explanation:

• fold: The command that will be applied to the specified file.
• -w5: Sets the maximum width for each line to 5 characters.
• -s: Signals the command to break lines at the spaces where possible, ensuring that whole words are prioritized over strict width compliance.
• path/to/file: Directs the command to the specific file whose lines need to be adjusted.

Example output:

Initial text:

Lorem ipsum dolor sit amet, consectetur adipiscing elit.

Result:

Lorem
ipsum
dolor
sit
amet,
consec
tetur
adipi
scing
elit.

Conclusion:

The fold command is versatile and useful for wrapping text to specified widths, which is crucial in environments requiring strict text formatting. Its various options allow for customization to suit specific width constraints while considering word boundaries, making it a vital tool in text processing tasks.