./fu.sh arquivo frase 1000

fu.sh

#!/bin/bash

if [ "$#" -ne 3 ]
then
	exit
fi

echo "arquivo: $1"
echo "tamanho: $3"
echo "frase: \"$2\""

> "$1"

tam="`du $1 | awk '{ print $1 }'`"

yes "$2" > "$1" &
pid_yes=$!

while [ "$tam"  -lt "$3" ]
do
	tam="`du $1 | awk '{ print $1 }'`"
	
	echo -en "$tam/$3\r"
done
kill "$pid_yes"

echo