Manipulating output with column and nl

Enhancing Terminal Outputs with column and nl in Linux

When working with text data or terminal outputs in Linux, formatting the data for better readability and analysis can often become necessary. Two powerful yet underutilized utilities that assist with this task are column and nl. These tools help in structuring the outputs effectively, making them easier to read and understand. This article explores how you can manipulate output using these tools and explains how to install them using different package managers like apt, dnf, and zypper.

Understanding column and nl

column is a utility that formats its input into multiple columns. Rows are filled before columns; you simply pipe output into column and it presents it in a nicely formatted table format. On the other hand, nl adds line numbers to its input, which is extremely useful for referencing or programming scenarios.

Installing column and nl

Most GNU/Linux distributions include column and nl with the default installation as part of the util-linux package and coreutils respectively. However, if for some reason they are not present, they can easily be installed.

• Debian/Ubuntu systems (using apt):

  sudo apt update
  sudo apt install bsdmainutils coreutils
  

• Fedora systems (using dnf):

  sudo dnf check-update
  sudo dnf install util-linux coreutils
  

• openSUSE systems (using zypper):

  sudo zypper refresh
  sudo zypper install util-linux coreutils
  

Using column to Format Output

The column tool is straightforward to use. For example, say you have a file named data.txt containing several rows of data separated by spaces:

name age location
Alice 30 New_York
Bob 25 Los_Angeles
Clara 22 Chicago

You can pipe this content directly into column like so:

cat data.txt | column -t

The -t option determines the number of columns based on the input file’s content. Here’s what the output would look like:

name   age  location
Alice  30   New_York
Bob    25   Los_Angeles
Clara  22   Chicago

Numbering Lines with nl

The nl command adds line numbers to each line. Running the following command will show numbering beside each line of your file:

nl data.txt

This outputs:

     1  name age location
     2  Alice 30 New_York
     3  Bob 25 Los_Angeles
     4  Clara 22 Chicago

Combining column and nl for Enhanced Output

Combining these tools can give you structured and numbered output, which can be extremely helpful for presenting data or debugging scripts.

cat data.txt | column -t | nl

This command will align all columns neatly and add a line number at the beginning of each line, enhancing both the readability and utility of the output.

Conclusion

The column and nl commands are simple yet powerful tools for formatting the output of text files or scripts in Linux. They are especially useful when you need to present data in a clearer format or when debugging scripts that require precise line references. By mastering these tools, Linux users can significantly improve their command-line efficiency and data handling capabilities.