Have you ever wanted to write a bunch of words just in the same line over and over again?
Many applications, like encoders or converters, do that in order to show dynamic information to the user without filling up the screen (and thus the terminal buffer).

Here is how you can do it easily in bash.

The code is quite simple:

while :; do
echo -n -e "\r$(date)"
sleep 1
done

The trick consists of three parts:

1. -n: we tell echo that we don’t want it to insert any new line character at the end of the string.
2. -e: we tell echo to translate any escaped sequence to the corresponding control character.
3. we use \r, which is simply a return carriage control character; this way, we always print in the same line over and over.

With the same approach we can develop a fancy text progress bar.
For example, here is a nice cp command equipped with a simple progress bar:

#!/bin/bash

bar_width=30
tick=0.2

if [ $# -ne 2 ]; then
    cat << EOM
$0: missing file operand
Use $0 filein fileout.
EOM
    exit 1
fi

function draw_progressbar() {

# parameters:
# $1 - actual size
# $2 - final size

    local part=$1
    local place=$((part*bar_width/$2))
    local i

    echo -en "\r$((part*100/total))% ["
   
    for i in $(seq 1 $bar_width); do
        [ "$i" -le "$place" ] && echo -n "#" || echo -n " ";
    done
    echo -n "]"

}

total=$(stat -c "%s" $1)

cp $1 $2 &

sleep $tick;
while fuser -s $2; do
    draw_progressbar $(stat -c "%s" $2) $total
    sleep $tick;   
done

draw_progressbar $(stat -c "%s" $2) $total
echo ""

References:

• “Can I do a spinner in BASH?” Q.33 of BASHFAQ on wooledge.org
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