[SOLVED] SED merging line

fievetl · 07-09-2012, 09:41 PM

Hi all,

I've been trying to merge several lines based on keyword on 2 different lines.

For example :
key1

key2

should become :
key1 key2

key1 can be found multiple time in the file, but I want to merge lines only when key2 is there 2 lines after.

It is pretty simple to do in vi :
:%s/key1\n\nkey2/key1 key2
but somehow it doesn't work with SED.

I've been surfing around the forum and all similar thread solution didn't work as well...

Any idea anyone ?
Thanks.

jschiwal · 07-09-2012, 11:24 PM

Sed reads and operates on lines of text. For 3 lines to be in the line buffer, You need to use the `N' command or add a line to the hold buffer with the `H' command.

dru8274 · 07-10-2012, 06:42 AM

Perhaps something like this...

Code:

# Firstly, create a data file
$ cat >data.dat <<EOF
one
key1
two
key2
three
EOF

$ sed -n '/^key1/ {N; N; s/^\(key1[^\n]*\)\n[^\n]*\n\(key2[^\n]*\)$/\1 \2/p }' data.dat
key1 key2

Happy with ur solution... Tick "yes" and mark as Solved!

fievetl · 07-10-2012, 07:10 AM

Thanks dru8274,

It helped. Now I can merge those three lines together, but somehow this is the only line in my result, now I need the rest of the file to remain untouched.
So I try to remove the search part /^key1/, but my result becomes empty.

Any idea ?
Thanks

dru8274 · 07-10-2012, 07:22 AM

And howabout this?

Code:

sed '/^key1/ {N; N; s/^\(key1[^\n]*\)\n\([^\n]*\)\n\(key2[^\n]*\)$/\1 \3\n\2/ }' data.dat

Happy with ur solution... Tick "yes", and mark as Solved

David the H. · 07-10-2012, 07:33 AM

sed is not well-designed for multi-line editing. It normally takes one line at a time into its edit buffer, minus the newline, applies the given expressions to it, and then re-adds the newline to any output afterwards.

For something like this you have to tell it to grab and store multiple lines at once with the "N" command (or perhaps by use of the hold buffer). Only then will there be literal newlines in the buffer for you to work with.

You'll also need to process the lines in a loop if you need to catch multiple sequential occurrences, as it replaces the whole buffer after each operation.

See here for how to handle your situation.
http://sed.sourceforge.net/sedfaq4.html#s4.25

Here are a few more useful sed references:
http://www.grymoire.com/Unix/Sed.html
http://sed.sourceforge.net/grabbag/
http://sed.sourceforge.net/sedfaq.html
http://sed.sourceforge.net/sed1line.txt

The grymoire tutorial in particular will give you all the basics.

fievetl · 07-10-2012, 08:18 AM

Wow, thanks dru8274,

I would have never found this on my own!
Problem solved

Appreciate it!