LinuxQuestions.org - [SOLVED] sed: delete blank lines and modify line immediately after such

- Programming (https://www.linuxquestions.org/questions/programming-9/)

- - sed: delete blank lines and modify line immediately after such (https://www.linuxquestions.org/questions/programming-9/sed-delete-blank-lines-and-modify-line-immediately-after-such-4175526274/)

sed: delete blank lines and modify line immediately after such

sed 4.2.2 on arch 3.18.0
I have many files containing multiple paragraphs of text. In some there are no blank lines and each paragraph begins with a single TAB character. This is the standard I wish to apply to all other files, so I want to remove all blank lines and prepend their following line with a TAB.

I believed the following sed script would do the job

Code:

~ $ sed '/\s*/ {

N

/\n[^\t]/ {

s/.*\n\([^\t].*\)/\t\1/

}

> }' p

but for this input in file p

Code:

drwxr-xr-x 12 root root 4096 Oct 18 09:36 var/



lrwxrwxrwx  1 root root    7 Jul  4 05:44 bin -> usr/bin/

drwxr-xr-x  3 root root 4096 Oct 18 09:34 boot/

lrwxrwxrwx  1 root root    7 Jul  4 05:44 lib -> usr/lib/

          

drwx------  2 root root 4096 Oct 18 02:36 lost+found/

drwxr-xr-x  2 root root 4096 Jul  4 05:44 mnt/

drwxrwxrwx 11 g    g    4096 Oct 20 10:59 opt/

dr-xr-xr-x 91 root root    0 Oct 20 07:28 proc/

I got the following output

Code:

drwxr-xr-x 12 root root 4096 Oct 18 09:36 var/



        drwxr-xr-x  3 root root 4096 Oct 18 09:34 boot/



        drwxr-xr-x  2 root root 4096 Jul  4 05:44 mnt/

        dr-xr-xr-x 91 root root    0 Oct 20 07:28 proc/

What am I doing wrong?

/\s*/ means nothing, it is useless, it matches always, if you want to specify empty lines use /^\s*$/ instead
sed is not able to do multi line search/replace, so using \n will not work
N will join two lines, that is ok, you just need to replace the empty line with a single tab before that.

Quote:

Originally Posted by pan64 (Post 5273874)

Not with any of the following

Code:

sed 's/^\s*$/\t/' N  p

sed 's/^\s*$/\t/' { N }  p

sed -e 's/^\s*$/\t/' -e '/^\t$/ { N }'  p

The substitution works fine, but not the join

How about something like:

Code:

sed -e '/^\s*$/{N;s/^\s*\n/\t/}'

Of course the very first line should be indented??

Quote:

Originally Posted by grail (Post 5274028)

How about something like:

Code:

sed -e '/^\s*$/{N;s/^\s*\n/\t/}'

Of course the very first line should be indented??

Thank you, that does the job perfectly. No problem about the first line, subsequent program assumes first line is a new paragraph.

Not that it is too important, but for future onlookers, the '-e' is not required. In my doodlings I was initially trying multiple sed statements joined together :)