How can I exclude the lines which matche the range patterns in sed?

Question

I am writing sed expression which tries to print the text within a range of patterns:

apt-cache showpkg gdm | sed -n '/Reverse Depends:/,/Dependencies:/ p'

This basically works, current output is:

Reverse Depends: 
  libgdm1:i386,gdm 3.8.3-3~
  ...
  ...
  gnome-control-center-data,gdm 3.0
Dependencies:

But I don't want the lines containing the patterns themselves, I want:

  libgdm1:i386,gdm 3.8.3-3~
  ...
  ...
  gnome-control-center-data,gdm 3.0

I know I can just just pipe the output to grep with -v option:

grep -v "Reverse Depends:"

But I hope sed has an option for it. I have tried

$ apt-cache showpkg gdm | sed -n '/Reverse Depends:/-1,/Dependencies:/-1 p'

But it doesn't work:

sed: -e expression #1, char 19: unknown command: `-'

@don_crissti That's excellent. Post that as an answer with a brief explanation of how it works! I'll upvote it. — Ben Kovitz, Apr 03 '18 at 23:40

score 4 · Accepted Answer · edited Apr 13 '17 at 12:36

4

Just delete everything between the first line and the first pattern, between the second pattern and the last line:

apt-cache showpkg gdm | sed '1,/Reverse Depends:/d;/Dependencies:/,$d'

Note that this approach will fail if your first pattern occurs on the first line and doing regexes checking more than is necessary can affect performance.

A better approach:

$ apt-cache showpkg gdm |
  sed -n '/Reverse Depends:/{
    :1
    n
    /Dependencies:/q
    p
    b1
  }'

edited Apr 13 '17 at 12:36

Community

answered Jan 25 '16 at 09:37

cuonglm

ah I wish I thought of that, thanks cuonglm! I will accept when stackexchange lets me :) – the_velour_fog Jan 25 '16 at 09:39
To get this to work I actually had to use apt-cache showpkg gdm | sed '1,/Reverse Depends:/d' | sed '/Dependencies:/,$d' for some reason it didnt work for me otherwise - using GNU sed. but the basic idea worked – the_velour_fog Jan 25 '16 at 10:28
@the_velour_fog: Please paste exact the command you run. I tried GNU sed without any issue. – cuonglm Jan 25 '16 at 10:29
when I used your command in a bash script and added a variable and redirected output to a file I was having problems - but now its working fine - so it obviously was my mistake!

1 Answers1