Have you ever found yourself needing to process CSV files and generate output in a structured table format? Not too long ago, I was dealing with a messy file that wasn't properly formatted. It had excessive spaces between each column, and I needed to convert it into CSV format for database upload. After cleaning it up and generating the CSV output, I found it difficult to visually verify the data's integrity because the formatting wasn't very clear. That’s when the column command became extremely useful for me.

According to the manpage, the column command is for "columnating lists." In simpler terms, it's a lightweight utility that allows you to format your data into a structured table format—organizing it into rows and columns—based on how your source file is laid out. The column command is part of the util-linux package.

An important thing to keep in mind is that the column command behaves differently on Debian-based and RHEL-based distributions. This is because Debian-based systems use the column utility from the bsdmainutils package instead of the one from util-linux. The version in util-linux is more up-to-date compared to the one in bsdmainutils. You can read more about this in the bug report.

<code>$ dpkg -S $(which column)</code>

For this demonstration, I'm using CentOS 7, and I’ll show you the differences between Ubuntu and CentOS 7. To check the version of the column command (and also the version of util-linux), run the following command. Note that this won’t work on Debian or Ubuntu systems.

<code>$ column --version  # does not work on Debian/ubuntu</code>

Alternatively, you can check the util-linux version using these commands:

<code>$ rpm -qa | grep -i util-linux   # for Redhat, Centos, Fedora, Amazon Linux
$ dpkg -l | grep -i util-linux    # for Ubuntu</code>

Before diving into the column command, it's a good idea to check the man page to explore all available options.

<code>$ man column</code>

Display File Content in Table Format

You can use the column command to convert a file into a table by passing the filename as an argument along with the -t option. For example, I'll use the /etc/passwd file as input.

<code>$ column -t /etc/passwd</code>

Looking at the image above, the output might not be what you expected—it may look odd. This is because column uses space as the default delimiter. This behavior can be changed by specifying a custom delimiter.

Using a Custom Delimiter

Custom delimiters offer more flexibility. Use the -s option followed by your desired delimiter. Let’s use ":" as the delimiter to format the /etc/passwd file properly.

<code>$ column -s ":"  -t /etc/passwd</code>

As you can see, the output is now neatly formatted. Starting from util-linux version 2.23, the -s option no longer treats multiple adjacent delimiters as one.

However, if you run the same command on Ubuntu, you'll notice that it does treat multiple delimiters as one. This is due to the version of column included in bsdmainutils.

<code>$ column -s ":"  -t /etc/passwd</code>

To fix this behavior on Debian or Ubuntu, use the -n flag.

<code>$ column -t -s ":" -n /etc/passwd             # Only on Debian/Ubuntu</code>

Skip or Include Empty Lines

By default, the column command ignores blank lines in the input file. Let’s say your input file is in CSV format and contains blank lines between entries. When you format it using column, those blank lines will be skipped.

<code>$ column -t -s ";" dummy.txt</code>

As shown in the image above, empty lines in dummy.txt are ignored when generating the table.

Note: This behavior is consistent across both bsdmainutils and util-linux versions of the column command. However, on Debian or Ubuntu, you can override this by using the -e flag.

<code>$ column -e -t -s "," dummy.txt        # Only on Debian/Ubuntu</code>

Now the table is generated correctly, and the empty lines are preserved.

Customize Output Separator

By default, two spaces are used as the separator between columns. You can change this by using the -o option. However, this feature is only available in the util-linux version of column (used in RHEL-based systems).

<code>$ column -t -s "," -o "||" dummy.txt    # Only on Rhel based distro</code>

Transpose Rows into Columns

Using the -x option, you can transpose rows into columns. This feature works the same way in both RHEL and Ubuntu variants of the column command. This can be particularly useful when you need to extract certain fields and make them headers in your CSV file.

<code>$ column -x fillcols.txt</code>

Alternatively, if you run the column command without any flags, it behaves the same as if you had used the -x flag.

Determine Terminal Column Width

The column command uses the ($COLUMNS) environment variable to determine the width of your terminal. Based on that, it adjusts how the table is displayed.

<code>$ echo $COLUMNS</code>

In the example below, I resized my terminal window so that $COLUMNS was set to 60, and then I ran the column command. I then resized the window again so that $COLUMNS was set to 114, and ran the same command again. You can clearly see the difference in how the table is displayed based on terminal size.

<code>$ column -t -s ":" /etc/passwd | head 5</code>

That wraps up this guide. If you have any suggestions or feedback, feel free to leave a comment below.

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