Golang Printing Tabstopped Text into Aligned Columns

May 5, 2019

One of the strengths of Golang as a language is it has a pretty strong standard library of packages out of the box. Things like the httptest package and even the http package is strong enough that there are countless http servers open sourced built on top of it. One of the hidden convenient packages I’ve used is the tabwriter to help print out tabstopped text into aligned text.

If you have written any kind of command line tools in go printing out results or output can be tedious to format with dynamic lenghts of the output. The tabwriter package in Go is a way to help with that as a standard built-in to the language. First you start out by creating the writer itself:

package main

import (
	"os"
	"text/tabwriter"
)

func main() {
	writer := tabwriter.NewWriter(os.Stdout, 0, 8, 1, '\t', tabwriter.AlignRight)
}

The NewWriter function takes in an io.Writer compatible type, which we will use STDOUT. Following that are the different spacing settings, first is the min cell width, next is the width of the tab characters in spaces, last is the padding added to each cell before the length is computed. After that is the character to use for the padding which is a \t tab character here. The last input is a modifier flag for the formatting of text, such as alignment.

Now lets use the writer to add some content to display connection info for sites. We will want to display a hostname, a port, along with a username/password combination.

package main

import (
	"fmt"
	"os"
	"text/tabwriter"
)

func main() {
	writer := tabwriter.NewWriter(os.Stdout, 0, 8, 1, '\t', tabwriter.AlignRight)
	fmt.Fprintln(writer, "host\tport\tuser\tpassword")
	fmt.Fprintln(writer, "localhost\t:4000\tadmin\tadmin123")
	fmt.Fprintln(writer, "admin.productionapp.com\t:43\tprod-admin\th^3asd2#r0ealk")
	writer.Flush()
}

Running this should give the output below:

host			port	user		password
localhost		:4000	admin		admin123
admin.productionapp.com	:43	prod-admin	h^3asd2#r0ealk

As you can see the alignment of the columns by tabstop are handled for you depending on the length calculation of the content between the tabstops. We have to use fmt.Fprintln here to write to the writer directly with out lines to be formatted by the tabwriter. Try playing around with some of the configurations to see how each option affects the output and formatting.

The code here is pretty simple to understand and allows for customization and all of this is built into the standard libary of packages in Golang which is nice. If you have ever had to implement this yourself or need to install 3rd-party packages to achieve this you will appreciate having this available to you at no extra cost.