col command in Linux with Examples

The col utility of Linux is excellent at stripping any reverse line feeds and instead replacing the whitespace characters with tabs wherever possible. They find it particularly handy when processing output from such commands as `nroff` and `tbl`. The `col` utility reads data from the standard input and writes it to the standard output. Thus, it is a convenient utility while processing text on pipelines.

Syntax

col [-bfhpx] [-l num]

Basic Example

Construct an example file called `sample.txt` with a message including reverse line feeds and whitespace:

sample.txt data

We then run the basic ‘col’ command without options:

cat sample.txt | col > output.txt

This command inputs and removes reverse line feeds, using optimized whitespace.

Basic col command example

Key Options of col command

1. -b (No Backspaces)

This option does not show the backspaces, printing instead only the last character written to each column position.

cat sample.txt | col -b > output_no_backspace.txt

2. -f (Forward Half Line Feeds)

This option allows half line feeds to be passed through, which may be useful for some formats of text.

cat sample.txt | col -f > output_half_line_feeds.txt

3. -h (Do Not Expand Multiple Spaces)

This option will not produce multiple spaces, but instead it will use tabbing where possible:

cat sample.txt | col -h > output_no_multiple_spaces.txt

4. -l (num Buffer Lines)

This option specifies the number of lines to buffer in memory; the default is 128 lines.

cat sample.txt | col -l 256 > output_buffered.txt

5. -p: Pass Unknown Control Sequences

This option allows unknown control sequences to pass without change, instead of being filtered.

cat sample.txt | col -p > output_pass_control.txt

6. -x: Output Multiple Spaces

This option prints multiple spaces for every tab. This could be necessary for certain types of layout format.

cat sample.txt | col -x > output_multiple_spaces.txt

Conclusion

The col command is a general-purpose tool under the Linux text processing toolkit. It is quite indispensable when formatting complex text such as man pages or at any other point of output in different text formatting tools. Further, knowing its different options and usage will enable you to control line feeds, whitespaces, and control characters in your text processing workflows effectively.