Sed regex - include original matching

Question

INPUT:

dsfgsdf8gfsd
2011.06.26. v
iudsfg98sdfg
sosdufgsdfg
2011.06.27. h
8xdofguiosdfg
jdasfhasd89fa
2011.06.28. k
ydsfgsdgsdg
dsfgdsfzfszgh
2011.06.29. sze
ds9fgisdfgsdfg
asdfasdfasddf
2011.06.30. cs
dsg789sdiofgsdg
dsfig89dsfgds
2011.07.01. p
sd9fg8sdgsdg
sdlfjgsd89öfgxcbv
dsglsd9gcxbv
dsflgjsdlfgfsdg
sdfsdfgdxfgxc
2011.07.02. szo
cvbdsgfsd
2011.07.03. v
dfgsdfgsd
2011.07.04. h
sdfgsdfgsdg

How can I get this OUTPUT with e.g.: sed? (or Perl?)

2011.06.26. v
iudsfg98sdfg
sosdufgsdfg
----------
2011.06.27. h
8xdofguiosdfg
jdasfhasd89fa
----------
2011.06.28. k
ydsfgsdgsdg
dsfgdsfzfszgh
----------
2011.06.29. sze
ds9fgisdfgsdfg
asdfasdfasddf
----------
2011.06.30. cs
dsg789sdiofgsdg
dsfig89dsfgds
----------
2011.07.01. p
sd9fg8sdgsdg
sdlfjgsd89öfgxcbv
dsglsd9gcxbv
dsflgjsdlfgfsdg
sdfsdfgdxfgxc
----------
2011.07.02. szo
cvbdsgfsd
----------
2011.07.03. v
dfgsdfgsd
----------
2011.07.04. h
sdfgsdfgsdg

So I want to swap the:

2011.06.26. v

AND

2011.06.27. h

etc. to this:

----------
2011.06.26. v

AND

----------
2011.06.27. h

I already tried (don't laugh :D ):

sed "s/[0-9]\{4\}\.[0-9]\{2\}\.[0-9]\{2\}\. /WTF/g"

But I don't know how to match "h, k, sze, cs, p, szo, v" in sed, and I don't know how can I put the matched things to the "WTF" (in .../WTF/g")

Has anyone any idea? :\

Thank you!

Answer 1

A starting point is this sed line:

$ echo 2011.06.26. v | sed 's/^\([0-9]\+\.[0-9]\+\.[0-9]\+\. \([hv]\|sze\)\)$/----------\n\1/'
----------
2011.06.26. v

Since sed uses basic regular expression syntax (by default), you have to escape the ()|+ characters to get their special meaning (grouping, alternative, one or more). With \1 you backreference the first group match.

Answer 2

I found this solution using sed:

sed -n '/^[0-9]\{4\}\.[01][0-9]\.[0123][0-9]\./,${:a;N;$!ba;{s/\([0-9]\{4\}\.[01][0-9]\.[0123][0-9]\.\)/--------------\n\1/g;p}}'

The disadvantage is that the date has to be matched twice. Maybe there's another (better) solution.
The output is exactly as you expect in your example.

Answer 3

In other words you want to insert the line ---------- before every line that contains a YYYY.MM.DD date followed by a space and a bunch of lowercase letters. There are several ways to do this. You can use the insert command (i):

sed -e '/^[0-9][0-9][0-9][0-9]\.[0-9][0-9]\.[0-9][0-9] [a-z][a-z]*$/ i \
----------'

Or you can replace the empty string at the beginning of the line by a newline.

sed -e '/^[0-9][0-9][0-9][0-9]\.[0-9][0-9]\.[0-9][0-9] [a-z][a-z]*$/ s/^/----------\
'

Or you can use & in the replacement text of an s command to stand for the matched pattern.

sed -e 's/^[0-9][0-9][0-9][0-9]\.[0-9][0-9]\.[0-9][0-9] [a-z][a-z]*$/----------\
&'

Some sed implementations allow you to write \n instead of backslash-newline in the replacement text, but on others \n prints \n or n.