How to delete and replace last line in the terminal using bash?

Question

I want to implement a progress bar showing elapsed seconds in bash. For this, I need to erase the last line shown on the screen (command \"clear\" erases all the screen, but

Answer 1

Can achieve it by placing carriage return \r.

In a single line of code with printf

for i in {10..1}; do printf "Counting down: $i\r" && sleep 1; done

or with echo -ne

for i in {10..1}; do echo -ne "Counting down: $i\r" && sleep 1; done

Answer 2

echo a carriage return with \r

seq 1 1000000 | while read i; do echo -en "\r$i"; done

from man echo:

-n     do not output the trailing newline
-e     enable interpretation of backslash escapes

\r     carriage return

Answer 3

In case the progress output is multi line, or the script would have already printed the new line character, you can jump lines up with something like:

printf "\033[5A"

which will make the cursor to jump 5 lines up. Then you can overwrite whatever you need.

If that wouldn't work you could try printf "\e[5A" or echo -e "\033[5A", which should have the same effect.

Basically, with escape sequences you can control almost everything in the screen.

Answer 4

The carriage return by itself only moves the cursor to the beginning of the line. That's OK if each new line of output is at least as long as the previous one, but if the new line is shorter, the previous line will not be completely overwritten, e.g.:

$ echo -e "abcdefghijklmnopqrstuvwxyz\r0123456789"
0123456789klmnopqrstuvwxyz

To actually clear the line for the new text, you can add \033[K after the \r:

$ echo -e "abcdefghijklmnopqrstuvwxyz\r\033[K0123456789"
0123456789

http://en.wikipedia.org/wiki/ANSI_escape_code

Answer 5

The \033 method didn't work for me. The \r method works but it doesn't actually erase anything, just puts the cursor at the beginning of the line. So if the new string is shorter than the old one you can see the leftover text at the end of the line. In the end tput was the best way to go. It has other uses besides the cursor stuff plus it comes pre-installed in many Linux & BSD distros so it should be available for most bash users.

#/bin/bash
tput sc # save cursor
printf "Something that I made up for this string"
sleep 1
tput rc;tput el # rc = restore cursor, el = erase to end of line
printf "Another message for testing"
sleep 1
tput rc;tput el
printf "Yet another one"
sleep 1
tput rc;tput el

Here's a little countdown script to play with:

#!/bin/bash
timeout () {
    tput sc
    time=$1; while [ $time -ge 0 ]; do
        tput rc; tput el
        printf "$2" $time
        ((time--))
        sleep 1
    done
    tput rc; tput ed;
}

timeout 10 "Self-destructing in %s"

Answer 6

Use the carriage return character:

echo -e "Foo\rBar" # Will print "Bar"