sed command search and replace

zulkifal · 11-23-2012, 10:04 AM

I have this problem where I am looking for a string and replacing it but the issue is that my search criteria returns multiple strings and i need to change only one e.g in /etc/sudoers file

#wheel......
#whel...... NO PASSWD

i only want to remove hash from the line that does not end with "NO PASSWD".I tried using line number method but this string seems to have a different line numbering on different systems. Any ideas?
Thanks

steelneck · 11-23-2012, 10:48 AM

You could pipe the inverted output from grep to sed, like this:

Code:

grep -v "NO PASS" /etc/sudoers | sed 's/#wheel/wheel/'

You may also know that you can use the -i option for sed to write the change to file instantly.

linosaurusroot · 11-23-2012, 11:27 AM

I'd advise against changing sudoers directly. Always write to a new file such as sudoers.tmp (with correct owner, group and mode) then use

Code:

visudo -c sudoers.tmp

to confirm satisfactory syntax. Finally rename the temp file to sudoers.

zulkifal · 11-23-2012, 12:04 PM

I agree with you "linosaurusroot".
Thanks "steelneck" for reply but that command doesnt seem to work. lets make it this way:
what is the right command to search for a string:
# %wheel ALL=(ALL) ALL

and replace it with

%wheel ALL=(ALL) ALL

keep in mind that we have a similar string like
# %wheel ALL=(ALL) NOPASSWD: ALL
in the same file
Thanks

linosaurusroot · 11-23-2012, 12:24 PM

You could cheat by having for each block of rules you are preparing to switch on and off surround them by comments:

Code:

groucho ALL=/bin/false
# begin wheel group all access
%wheel ALL=(ALL) ALL
# end wheel group all access
harpo ALL=/bin/true

wax on

Code:

sed -i '/# begin wheel/,/# end wheel/s/^#%\(.*\)/%\1/'   sudoers.tmp

wax off

Code:

 sed -i '/# begin wheel/,/# end wheel/s/^\(%wheel\)/#\1/'  sudoers.tmp

steelneck · 11-24-2012, 10:19 AM

Quote:

Originally Posted by zulkifal

Thanks "steelneck" for reply but that command doesnt seem to work.

Well, in first post you wrote "NO PASSWD" and now it is "NOPASSWD", could that be the root to that my line did not work for you?

As to the question you wrote now:

Code:

sed 's/# %wheel ALL=(ALL) ALL/%wheel ALL=(ALL) ALL/'

That one will not hit the line containing NOPASSWD

zulkifal · 11-26-2012, 08:19 AM

Thx steelneck , by the way "linosaurusroot" . can you explain what you wrote? bcause i didnt get it.

schneidz · 11-26-2012, 10:01 AM

this worx for me:

Code:

 [schneidz@hyper ~]$ sed s/'# %wheel ALL=(ALL) ALL'/'%wheel ALL=(ALL) ALL'/ sudo.tmp
%wheel ALL=(ALL) ALL

zulkifal · 11-26-2012, 10:56 AM

Its working now . Thanks everyone