1 min read

How to Build a Textual Progress Bar for CLI and Terminal Apps

March 06, 2020
tags: cli, node, terminal

I find textual interfaces extremely interesting and I’m trying to figure out how some common components can be creates

this is the time of a progress bar


to create a textual progress bar we need to understand two simple concepts

  • you can control where the cursor Is programmatically
  • There are ANSI escapes code to cancel the entire screen or the current line (\r)

One way to achieve this is to start a loop and on every iteration print the special escape code \r that will clear the line at the cursor position and then print one of the following to simulate a progress

[.        ]
[..       ]
[...      ]
[....     ]
[.....    ]
[......   ]
[.......  ]
[........ ]

In this example, I’ll be using Node.js

async function main() {
  /* using 20 to make the progress bar length 20 charactes, multiplying by 5 below to arrive to 100 */

  for (let i = 0; i <= 20; i++) {
    const dots = ".".repeat(i)
    const left = 20 - i
    const empty = " ".repeat(left)

    /* need to use  `process.stdout.write` becuase console.log print a newline character */
    /* \r clear the current line and then print the other characters making it looks like it refresh*/
    process.stdout.write(`\r[${dots}${empty}] ${i * 5}%`)
    await wait(80)


function wait(ms) {
  return new Promise(res => setTimeout(res, ms))

This was relatively simple but with some custom colors can have a huge impact in the UX of a tool, especially it takes some time to complete and there is no other feedback for the user that everything is going ok

full code available on the repo on github

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Blog by Jaga Santagostino.
Software consultant, polyglot developer, maker of things, lifelong learner.
ReactJS Milano & milano.dev organizer