Using sed to replace numbers with @ inserts @ between every character

Question

I want to replaced all number with '@' symbol. I am using the below sed command , but not getting the desired result.

command -

echo "abc 434 pankaj 444" | sed 's/[0-9]*/@/g'

Result -

@a@b@c@ @ @p@a@n@k@a@j@ @

Answer 1

Well, quite simply, [0-9]* matches strings that consist entirely of zero or more digits, include empty strings. Anything that matches an empty string, matches between any two characters, so the replacement @ is added between all letters in the input. Strings of multiple digits are replaced with one @ since the expression matches all consecutive digits at once.

So in the input string ab43 the matches to [0-9]+ are (with some whitespace added for clarity):

    a   b   434
  ^   ^     ^^^- here, a string of some digits
  ^   ^- here, a zero-length string
  ^- here, a zero-length string

Use [0-9] to match exactly one digit, or [0-9][0-9]* to match one or more (or [0-9]+ in extended regular expressions).