is there a way i can either insert a character into a line or substitute and arbitrary character with itself plus some other carachter(s) in sed?

Question

like say i have a string of numbers that constitute a phone number and are like so

##########

and i want to format them like :

###-###-####

insert only puts in new lines, and i dont know how to make say an expression like

sed (s/[0-9]/TheNumberIFound-/)//3//6

so is there some way i can ask sed to just add something after a matched pattern, or to replace the matched pattern with itself plus some other char?

Answer 1

$ echo "1234567890" | sed -re 's/([0-9]{3})([0-9]{3})([0-9]{4})/\1-\2-\3/g'
123-456-7890

• [0-9] does match any digit in one position in the phone number.
• {3} tells sed to match the pattern prepended to this, 3 times.
• The ( and ) (parentheses) surrounding the three repeats of these logs the matched numbers in "memories"
  the "memories" are then "recalled" with \1 for the first parenthese, \2 for the second and so on.
• Therefore \1-\2-\3 makes your reformatted phone number.
• Add the g at the end to make sed do this more than once per line.

Intentionally attempted to keep language at 'noob' level ;-p