Prepend certain lines of file

Question

I'd like to create a script to comment out lines of my Mac OS X hosts file that contain .com. And also one to reverse it.

So this:

127.0.0.1    foo.com
127.0.0.1    bar.com
127.0.0.1    baz
127.0.0.1    qux

would become:

#127.0.0.1   foo.com
#127.0.0.1   bar.com
127.0.0.1    baz
127.0.0.1    qux

I looked around on Google and the sed man page and tried a few things with bash and sed, but I haven't come close.

sed 's/^/^#/' | grep '.com' < hosts

grep '.com' | sed 's/^/^#/' < hosts

Thank you for any help!

try this http://stackoverflow.com/questions/742466/how-can-i-reverse-the-order-of-lines-in-a-file — Fredrik Pihl, Feb 05 '13 at 19:11
doh, nothing except OP stated "And also one to reverse it." hence the link above — Fredrik Pihl, Feb 05 '13 at 19:17
That's another interpretation which, when you state it sounds more reasonable :-) — Fredrik Pihl, Feb 05 '13 at 19:24

Barmar · Accepted Answer · 2013-02-05T19:23:06.467

7

sed '/\.com/s/^/#/' < hosts

Interpretation:

If you want to replace the original file, use sed's -i option:

sed -i.bak '/\.com/s/^/#/' hosts

This will rename hosts to hosts.bak and create a new hosts with the updated contents.

To undo it, use:

sed -i.bak '/^#.*\.com/s/^#//' hosts

edited Feb 05 '13 at 19:23

answered Feb 05 '13 at 19:11

Barmar

I think OP wants it to be saved onto a file cause if he wanted it at stdout he could have just added a `cat ` in front of his command and it would work – noMAD Feb 05 '13 at 19:22
@noMAD He used input redirection, which is the same thing. But I updated my answer to show how to replace with sed. – Barmar Feb 05 '13 at 19:25

score 0 · Answer 2 · answered Feb 06 '13 at 01:28

0

With awk

awk '$2 ~ /.com/{$0 = "#"$0;}{print}' temp.txt

Output

#127.0.0.1    foo.com
#127.0.0.1    bar.com
127.0.0.1    baz
127.0.0.1    qux

answered Feb 06 '13 at 01:28

Mirage

2 Answers2