I'm trying to find the best regular expression to extract a version number from a string. For example:

 echo "Version (release mode)" | sed -ne 's/.*\([0-9]\+\.[0-9]\+\.[0-9]\+\.[0-9]\+\).*/\1/p'

The problem here is that it works only if the version number is in the format "a.b.c.d". If someone decides to add or remove a digit ("a.b.c.d.e", "a.b.c"), it will break. So I'd like to factorize the regex and tell sed that I want:

(1 or more numbers followed by a dot) x 1 or more times, followed by a number.

I can't find how to "group" the "1 or more numbers followed by a dot" so I can tell I want that pattern at least once. I've tried this but it doesn't work:


Any ideas ?


Try next 'sed' command:

$ echo "Version (release mode)" | sed -ne 's/[^0-9]*\(\([0-9]\.\)\{0,4\}[0-9][^.]\).*/\1/p'

It uses the {i,j} syntax, which selects the expression a number of times between the first and the last number. There souldn't be any numbers in the string before the version number.

Another examples:

$ echo "Version (release mode)" | sed -ne 's/[^0-9]*\(\([0-9]\.\)\{0,4\}[0-9][^.]\).*/\1/p' 
$ echo "Version 1.2 (release mode)" | sed -ne 's/[^0-9]*\(\([0-9]\.\)\{0,4\}[0-9][^.]\).*/\1/p'
$ echo "Version 1.2. (release mode)" | sed -ne 's/[^0-9]*\(\([0-9]\.\)\{0,4\}[0-9][^.]\).*/\1/p'

EDIT to comments:

$ echo "Version (release mode)" | sed -nre 's/^[^0-9]*(([0-9]+\.)*[0-9]+).*/\1/p'
  • You're specifying here the number of digits you want. What I want is that it works with any number of digits. – liberforce Dec 2 '11 at 18:01
  • I've edited the answer. I hope it works now. – Birei Dec 2 '11 at 21:33
  • I would fail on for example, but I got the general idea, thanks. – liberforce Dec 5 '11 at 11:06
  • I finally modified a bit your last answer to work with number with several digits, and added the syntax of extended regexp that Vinicius pointed me out. This gave me: echo "Version (release mode)" | sed -nre 's/^[^0-9]*(([0-9]+\.)*[0-9]+).*/\1/p'. Thanks to both of you for your answers ! – liberforce Dec 5 '11 at 12:18
  • I've edited the answer to show the final correct 'sed' command. Thank you. – Birei Dec 5 '11 at 16:36

Try this:


It means "match 1 or more digits and then match any number of (dot + digits)".

  • I've tried but you forgot to escape characters, so I tried several different combinations, but it failed even with escaping, unless I didn't find the right one. – liberforce Dec 2 '11 at 18:03
  • 1
    You have to pass the -E flag so that the regex will be interpreted as an extended regex, like in: sed -E -e 's/[0-9]+($|\.[0-9]+)*/x/g' in.txt > out.txt – Vinicius Pinto Dec 2 '11 at 23:08
  • I'm using sed on MinGW, and it looks like -E doesn't exist on that version (sed 4.2.1). That option is renamed -r or --regexp-extended. Thanks for the tip. – liberforce Dec 5 '11 at 11:09

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