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@ @
  • 1
    echo "abc 434 pankaj 444" | sed 's/[0-9]/@/g' Dec 3, 2017 at 16:32

6 Answers 6


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).

  • then the regex pattern should replace all alphabets with '@' symbols, since alphabets has zero digits. Dec 3, 2017 at 17:20
  • @PankajPandey, err, right. I rephrased that a bit.
    – ilkkachu
    Dec 3, 2017 at 17:26
  • @PankajPandey, should they be? Neither [0-9]* nor [0-9] match any letters, and I thought you wanted to replace only numbers?
    – ilkkachu
    Dec 3, 2017 at 17:37
  • by that logic, alphabetic characters should also be replaced by '@' since they also do not match to any of the digits. Dec 3, 2017 at 17:38
  • i just want to understand the behaviour of sed command, as I feel it's behaviour is somewhat erratic. Dec 3, 2017 at 17:38

Replace each digit with @

echo "abc 434 pankaj 444" | sed 's/[0-9]/\@/g'
#Output: abc @@@ pankaj @@@

or replace each number with @

echo "abc 434 pankaj 444" | sed 's/[0-9]\+/\@/g'
#Output: abc @ pankaj @

depending on the desired output you need

  • Why escape the @ in the replacement, and why -E? Also, why not tr '0-9' '@'? However, this would replace all digits with @, not all numbers. One could potentially read the question in a way that means that the wanted output should be abc @ pankaj @.
    – Kusalananda
    Sep 9, 2020 at 12:39
  • Note that \+ is a GNU extension. The standard equivalent is \{1,\}. With -E (soon to be standard), you can use + or {1,}. Sep 9, 2020 at 13:01
echo "abc 434 pankaj 444"| tr "[0-9]" "@"

abc @@@ pankaj @@@

Replace * with any special character can be achieved by using tr command.

mystring="This is my number: 12345"
echo $mystring | sed 's/[0-9]/*/g'
  • 2
    tr is certainly one tool that can be used. But your example doesn't explain how - you used sed, not tr. Also your answer suggests that what OP wants to do requires a script and a variable - surely this is not what you want to say? Sep 25, 2021 at 20:03

Depending on whether you want to replace digits or whole numbers (runs of consecutive digits) with @, you may use the tr command without or with its -s option:

$ echo "abc 434 pankaj 444" | tr '[:digit:]' '[@*]'
abc @@@ pankaj @@@
$ echo "abc 434 pankaj 444" | tr -s '[:digit:]' '[@*]'
abc @ pankaj @

The -s option of tr makes the utility "squeeze" any consecutively occurring character from the second argument found in the data. In this case, using -s makes tr combine runs of @ characters into single @ characters.

The two arguments [:digit:] and [@*] tell tr to replace digits with @ characters. Most (all?) implementations of tr allow you to write @ in place of [@*] as the second argument. The [@*] literally means "as many @ as there are characters in the set described by the first argument".

Note that tr will squeeze any pre-existing runs of consecutive @ characters in the input if -s is in effect.

Your approach with sed does not work as expected because you insert a @ character wherever there are zero or more matches of a digit. There are zero digits between each character in the input, so the expression matches between each character.

A modified substitution that would work correctly and replace runs of digits with a single @ would be

sed 's/[[:digit:]]\{1,\}/@/g'

By using \{1,\} in place of * (which in itself is the same as \{0,\}) we force at least one match of the preceding expression. You will see \{1,\} written as + in extended regular expressions.

By removing \{1,\} from the expression, leaving the substitution as s/[[:digit:]]/@/g, you replace each individual digit with a @.

  • 1
    Beware though that echo @@123@@ | tr -s '[:digit:]' '[@*]' outputs @ Sep 26, 2021 at 15:50
  • @StéphaneChazelas That's a big whoops. I will add the necessary notices to the text. Thanks!
    – Kusalananda
    Sep 26, 2021 at 16:12

You can achieve this by awk command too

echo "abc 434 pankaj 444" |awk '{gsub("[0-9]","@",$0);print $0}'

  • 1
    While true, sed is the right tool for the job and will work given a small modification. Dec 3, 2017 at 18:24

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