Shell Programming and Scripting

a=${number:0:3}
b=${number:3:3}
c=${number:6:4}
echo "$a-$b-$c"

m=${nr#????};
echo ${nr%??????}-${m%???}-${nr#???????}

echo 1234567890 | sed 's/\(.\{3\}\)/&-/1;s/\(.\{7\}\)/&-/'

echo $nr|sed -r 's/(....)(...)(...)/\1-\2-\3/'

echo $nr|sed 's/\(....\)\(...\)\(...\)/\1-\2-\3/'

$ echo 1234567890 |awk '{print substr($0,1,3),substr($0,4,3),substr($0,7,4)}' OFS="-"
123-456-7890

echo 1234567890 | awk '{for(i=0;++i<=NF;)printf ((i~/4|7/)?"-"$i:$i)}' FS=