Overview
fmt optimizes the line length of text paragraphs to enhance readability. By default, it wraps lines to a width of 75 characters, but this can be adjusted using the -w option.
Key Features
- Reformats text paragraph line breaks
- Outputs to a specified width
- Processes standard input and files
- Offers various formatting options
Key Options
Formatting
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Usage Examples
Basic Formatting (75-character width)
echo "This is a very long sentence. The fmt command can be used to reformat the line breaks of this sentence. It helps improve readability." | fmtFormats text from standard input to the default width (75 characters).
Formatting to a Specific Width (e.g., 40 characters)
echo "This is a very long sentence. The fmt command can be used to reformat the line breaks of this sentence. It helps improve readability." | fmt -w 40Uses the -w option to set the maximum width of output lines to 40 characters.
Formatting File Content
printf "This is a very long line that needs to be formatted. It will be wrapped to the default width.\n" > example.txt
fmt example.txt
rm example.txtReads the content of a file, formats it, and outputs the result to standard output.
Splitting Long Lines Without Joining Short Ones
echo -e "Short line.\nThis is a very long sentence. The fmt command can be used to reformat the line breaks of this sentence. It helps improve readability." | fmt -sUses the -s option to split only long lines, keeping short lines as they are.
Formatting Comment Blocks
echo -e "# This is a very long comment line that needs to be formatted to a specific width.\n# It should only affect lines starting with a hash symbol." | fmt -w 50 -p "#"Uses the -p option to format only lines starting with a specific prefix.
Tips & Notes
fmt is primarily optimized for formatting paragraphs in plain text files. It may not be suitable for code or structured data.
Usage Tips
- Automatic line wrapping for long lines when writing emails
- Aligning paragraphs in README files or documents
- Using pipes (|) to combine with other commands
Notes
fmt operates on paragraphs, so text not separated by blank lines may be treated as a single long paragraph. For formatting code or script files, it is recommended to use dedicated tools like `clang-format` or `prettier`.