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I want to use sed to change the following text:

(3)www(5)first(3)nth(6)domain(3)com(0)

to:

www.first.nth.domain.com

Can each group between the parenthesis separators be captured and then reconstructed in order with period separators assuming that there will be from 2 to n+3 groups (infinity)? Is there another way?

I am already familiar with:

s/\(\d+\)/./g

but that only yields:

.www.first.nth.domain.com.
  • For the purposes of the RE is the number in brackets relevant? – roaima Mar 15 '16 at 19:53
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    Nothing stopping you from removing the first and last dot. – don_crissti Mar 15 '16 at 20:03
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This appears to satisfy your requirement. I'm not entirely sure whether you are looking to use the numbers in the brackets to validate the run-lengths, but I'm assuming not.

echo '(3)www(5)first(3)nth(6)domain(3)com(0)' |
sed -r -e 's/^\([0-9]+\)//' -e 's/(.)\([0-9]+\)(.)/\1.\2/g' -e 's/\([0-9]+\)$//'
www.first.nth.domain.com

The sed uses three different REs. The first and last strip off the bounded leading and trailing (\d+) expressions. The middle one strips the remainder.

  • basically three passes of sed? Is there no way to do it in just one pass? There is a reason for needing just one pass (sedcmd). – landen99 Mar 15 '16 at 20:29
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    @landen99 one pass with three operations. Try it. – roaima Mar 15 '16 at 21:51
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How about s/\([0-9]+\)/./g; s/^\.|\.$//g?

Your \d construction won't be recognized by some sed implementations. The above is a Posix extended regular expression. Which, you know, should work.

The trick in sed is just to work incrementally. You got most of the way there by replacing the parenthesized digits; you just didn't realize you could clean up the result with a second regex.

  • The thing is that extended regex is not (yet) supported by POSIX sed. You'll have to use BRE for full portability. – don_crissti Mar 15 '16 at 20:42

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