fold - Linux

Overview

The fold command in Linux is used to wrap each input line to fit a specified width. It is primarily used to ensure that long lines of text fit within a certain width for better readability in devices or windows that cannot horizontally scroll. This command is very useful when dealing with text outputs or files in terminal that do not automatically wrap text, or when formatting output in scripts and text processors.

Syntax

The basic syntax of the fold command is:

fold [OPTION]... [FILE]...

If no FILE is specified, or when FILE is -, fold reads from standard input.

Options/Flags

  • -b, --bytes: Count bytes rather than columns, which means control characters (like tab and backspace) are treated as having width 1.
  • -s, --spaces: Break lines at spaces. Makes the output more readable, as lines are broken at space characters closest to the specified width.
  • -w, --width=WIDTH: Use WIDTH columns instead of the default 80. This option specifies the maximum line width. If WIDTH is set to a smaller size than the longest word, that word appears on its own line but not folded.
  • --help: Display a help message and exit.
  • --version: Output version information and exit.

Examples

Example 1: Wrap text from a file to a width of 50 columns:

fold -w 50 filename.txt

Example 2: Wrap the standard input (from a pipe) and break lines at spaces:

cat longtextfile.txt | fold -s -w 60

Example 3: Wrap text counting bytes instead of column width:

echo "This is a tab:	" | fold -b -w 10

Common Issues

  • Long Words: fold does not split individual words. If a word is longer than the line width, it will not wrap, potentially causing formatting problems.

  • Non-Uniform Handling of Tabs and Control Characters: Without the -b flag, tabs and other control characters are treated differently, which may not reflect the actual visual layout.

    Solution: Use -b flag if an exact alignment is important, keeping in mind that it treats every character as having equal width.

Integration

fold can be combined with other commands to format and present text data effectively. For example, to view a wrapped log file in real time:

tail -f /var/log/syslog | fold -w 80

Or, integrate fold with grep to search and neatly display long lines:

grep 'error' /var/log/syslog | fold -w 80
  • fmt: Similar to fold, but tries to balance line lengths and does not break words.
  • cut: Used to remove sections from each line of files.
  • cat: Concatenate and display files.

For more reading and resources, refer to the GNU Coreutils: https://www.gnu.org/software/coreutils/manual/coreutils.html