How to print out to the same line, overriding previous line?

Question

Sometimes I see some commands in the terminal that print results to stdout but in the same line. For example wget prints an arrow like below:

0[=>        ]100%
0[  =>      ]100%
0[    =>    ]100%
0[      =>  ]100%
0[        =>]100%

but it is printed out to the same line so it looks like the arrow is moving. How can I achieve the same thing in my programs using bash or sh? Do I need to use other tools?

UPDATE:

I know I mentioned wget, which comes by default in linux, GNU based unices ... Is there a general approach that works on BSDs too? (like OSX) -> OK, If I use bash instead of sh then it works :)

Answer 1

You can also use ANSI/VT100 terminal escape sequences to achieve this.

Here is a short example. Of course you can combine the printf statements to one.

#!/bin/bash

MAX=60
ARR=( $(eval echo {1..${MAX}}) )

for i in ${ARR[*]} ; do 
    # delete from the current position to the start of the line
    printf "\e[2K"
    # print '[' and place '=>' at the $i'th column
    printf "[\e[%uC=>" ${i}
    # place trailing ']' at the ($MAX+1-$i)'th column
    printf "\e[%uC]" $((${MAX}+1-${i}))
    # print trailing '100%' and move the cursor one row up
    printf " 100%% \e[1A\n"

    sleep 0.1
done

printf "\n"

With escape sequences you have the most control over your terminal screen.

You can find an overview of possible sequences at [1].

[1] http://ascii-table.com/ansi-escape-sequences-vt-100.php

Answer 2

You can use \r for this purpose:

For example this will keep updating the current time in the same line:

while true; do echo -ne "$(date)\r"; done

Answer 3

Use the special character \r. It returns to the beginning of the line without going to the next one.

for i in {1..10} ; do
    echo -n '['
    for ((j=0; j<i; j++)) ; do echo -n ' '; done
    echo -n '=>'
    for ((j=i; j<10; j++)) ; do echo -n ' '; done
    echo -n "] $i"0% $'\r'
    sleep 1
done