cat - <<eofx >MyFile.txt
1-àèìòù-
2-áéíóú-
3-àèìòù-
4-âêîôû-
5-ãëïõü-
6-äåæö
eofx
echo "+-- MyFile.txt --------------------"
cat MyFile.txt
echo "+------------------------------"
awk '
BEGIN {
c["a"]="àáâãäåæ";
c["e"]="èéêë";
c["i"]="ìíîï";
c["o"]="òóôõö";
c["u"]="ùúûü";}
{r=$0;
for (x in c) {
for (i=1;i<=length(c[x]);i++) {
gsub(substr(c[x],i,1),x,r)}
} print "+- %s"$0" to "r;
}' MyFile.txt