Cool bash stuff with ANSI escape codes

Let’s see a few fun stuff you can do with a bit of bash and ANSI escape codes

Example #1: ASCII Progress bar

You know a script is cool when it shows a progress bar. And you write only cool scripts, right?

For this, we don’t need fancy stuff, just the \r char will do the magic for us. Let’s also assume you have a percentage variable lying around with display the progress of whatever unoptimized thing you’re doing as an integer from 0 to 100.

Python is our friend, and lets us roll with this one-liner:

print('\r[' + '#'*percentage + ' '*(100 - percentage) + ']', end=' ')

Pretty straightforward, right? But I hear you, you’re not using python, you’re making a script, so take this bash two-liner:

$ bar=$(printf "%100s" | tr ' ' '#')
$ printf "\r[${bar:0:$percentage}%$((100 - percentage))s]"

Ok so there’s some bash fancy stuff. Let’s decompose that a bit:

$(printf "%100s" | tr ' ' '#') - makes a string with 100 spaces, and replaces them with #
${bar:0:$percentage} bash’s magic variable substitution, works like python’s bar[0:percentage]
%$((100 - percentage))s printing the remaining spaces until we get to a length of 100

For specimen demonstration purposes, I stuck that in a loop for you to show it off:

bar=$(printf "%100s" | tr ' ' '#')
for i in {1..100}; do
	printf "\r[${bar:0:$i}%$((100 - i))s]"
	sleep 0.03
done

Results:

Using the escape sequence\x1b[y;xH we can move the cursor to the (x,y) coordinates in the terminal. We also know that \e[?25l hides the cursor and \e[?25h shows it back.

#!/bin/bash

# get terminal size
read LINES COLUMNS < <(stty size)

# available selections (colon separated)
IFS=: read -a text <<< "selection #1:selection #2:selection #3:selection #4" 
w=30
h=$((${#text[@]}+1))
x=$((COLUMNS/2 - w/2))
y=$((LINES/2 - h/2))

sel=0

# hide cursor
printf "\e[?25l"

# line (bool vert, int x, int y, int len)
function line () {
	if [[ $1 == v ]]; then
		for (( i = 1; i < $4; i++)); do
			printf "\x1b[$(($3 + $i));$(($2))H|"
		done
	else 
		for (( i = 1; i < $4; i++)); do
			printf "\x1b[$(($3));$(($2 + $i))H-"
		done
	fi
}

while true; do
	# erase screen
	printf "\x1b[2J"

	# box borders
	line h $x       $y       $w
	line h $x       $((y+h)) $w
	line v $x       $y       $h
	line v $((x+w)) $y       $h

	# box corners
	printf "\x1b[$((y+h));$((x+w))H+"
	printf "\x1b[$((y));$((x+w))H+"
	printf "\x1b[$((y+h));$((x))H+"
	printf "\x1b[$((y));$((x))H+"

	# display text selections
	for ((i = 0; i < ${#text[@]}; i++)); do
		printf "\x1b[$((y+i+1));$((x+w/2-${#text[i]}/2))H"
		if [[ $sel -eq $i ]]; then
			printf "\x1b[41;1m${text[i]}\x1b[0m"
		else
			printf "${text[i]}"
		fi
	done

	# read only one char of input
	read -sn1 input
	case $input in
		j)  sel=$(((sel+1) % ${#text[@]})) ;;
		k)  sel=$(((sel-1) % ${#text[@]}))
			if [[ sel -lt 0 ]]; then sel=3; fi ;;
		"") printf "\x1b[$((y+h+1));0H"
			echo "You selected ${text[$sel]}"
			break ;;
		q)  break ;;
	esac
done

# show cursor when we're done
printf "\e[?25h"

This is the result, moving the selection up and down with j and k keys:

Cool bash stuff with ANSI escape codes

Example #1: ASCII Progress bar

Example #2: bash selection menu