[SOLVED] sed question

I want to append a line after a particular set of lines in httpd.conf. There are multiple lines that match the one string, but if I add in the previous line, I can find the correct location with:

sed -nE '{N; /\s+#\s+Require all granted/p }' httpd.conf

gives me:

    #
    Require all granted

Now I want to add some lines after that, but not getting it to work. Any suggestions? I want to add: AllowMethods GET

Originally Posted by bradvan I want to append a line after a particular set of lines in httpd.conf. There are multiple lines that match the one string, but if I add in the previous line, I can find the correct location with: sed -nE '{N; /\s+#\s+Require all granted/{=;p} ; D}' httpd.conf gives me: 156 # Require all granted Now I want to add some lines after that, but not getting it to work. Any suggestions? I want to add: AllowMethods GET

You can use a to append what you want:

sed -nr 'N; /\s+#\s+Require all granted/{=;p;a AllowMethods GET
};D' conf

Notice, that everything that comes after a will be appended, i.e., you need a new line to continue the sed script.

On a side note, I do not know your exact requirement, but your script will only matches the first 'Require ...' in this snippet:

    #
    Require all granted

    #
    Require other granted

    #
    Require yet another granted

Thanks! In the httpd.conf file that I have, of the three matches, only one is preceded by a blank comment and that is the one I wish to append to. So, got this to work:

sed -i -r 'N; /\s+#\s+Require all granted/ a \
    AllowedMethods GET ' httpd.conf

which results in:

    #
    Require all granted
    AllowedMethods GET

which is what I want. Thanks!

just need to check somehow if that line was already there.

A simple grep for AllowedMethods. I only need it in once.

Originally Posted by bradvan Thanks! In the httpd.conf file that I have, of the three matches, only one is preceded by a blank comment and that is the one I wish to append to. So, got this to work: sed -i -r 'N; /\s+#\s+Require all granted/ a \ AllowedMethods GET ' httpd.conf which results in: # Require all granted AllowedMethods GET which is what I want. Thanks!

I just noticed that you removed the command 'D' from your sed. If you do this then you will only match on even lines, i.e., this will match:

$ cat sample.conf
    #
    Require all granted # line number 2

This, however will not match because the 'Require ...' part is on an odd line:

$ cat sample.conf
    An empty line
    #
    Require all granted # line number 3

So you may want to add back the command 'D' to delete up to the first newline.

Originally Posted by bradvan A simple grep for AllowedMethods. I only need it in once.

And what if There were multiple lines that may match that string

The O/P said it can only occur once.

Regarding the D command, this is a good point. But it deletes (up to an embedded \n) so it should be rather P;D
Print then delete!

Originally Posted by MadeInGermany Regarding the D command, this is a good point. But it deletes (up to an embedded \n) so it should be rather P;D Print then delete!

Good catch! I only tested with a hastily improvised dataset, focused on identifying the line in question and totally missed that.

Originally Posted by MadeInGermany The O/P said it can only occur once.

As long as the script/sed was not executed.
I would rather suggest a solution which can be executed several times without problems...

Argh! It doesn't work if I remove a blank line above it! Note: this is a script/set of instructions for setting up a kickstart server. So, this will only get run at the time of setting it up. The stock httpd.conf file does not have any AllowMethods statements in it. So a simple grep for that phrase will suffice to test whether or not to run the sed. Now, I can't quite get the sed to run with that blank line removed. Can't quite figure out how to drop the line from the pattern space. This works for the odd number of lines:

sed -i -r 'N; /\s+#\s+Require all granted/ a \
    AllowedMethods GET ' httpd.conf

(Also note that I am trying to edit the line; earlier I was just doing a search to test out the matching.) If it is easier to not edit in place, I can always send to a dummy file then move it back.

Originally Posted by bradvan Argh! It doesn't work if I remove a blank line above it! Note: this is a script/set of instructions for setting up a kickstart server. So, this will only get run at the time of setting it up. The stock httpd.conf file does not have any AllowMethods statements in it. So a simple grep for that phrase will suffice to test whether or not to run the sed. Now, I can't quite get the sed to run with that blank line removed. Can't quite figure out how to drop the line from the pattern space. This works for the odd number of lines: sed -i -r 'N; /\s+#\s+Require all granted/ a \ AllowedMethods GET ' httpd.conf (Also note that I am trying to edit the line; earlier I was just doing a search to test out the matching.) If it is easier to not edit in place, I can always send to a dummy file then move it back.

Yes, that is what I meant in my post #6. Try this:

sed -r 'N; /\s+#\s+Require all granted/{a \
    AllowMethods GET
b;};P;D' conf

Remember, that only a newline can terminate the a command inside the sed script.

PS: The -i switch should not affect the result, so just adding once you are satisfied should be fine.

Another solution: only run N command when the first line was met:

sed -r '/\s+#\s*$/{
    N; s/(\n\s*)Require all granted/\1AllowedMethods GET&/
  }' httpd.conf

The 2nd line is done by an s command. It allows to "inherit" the leading spaces.
The & is what matched before. So you can easily switch the order:

sed -r '/\s+#\s*$/{
    N; s/(\n\s*)Require all granted/&\1AllowedMethods GET/
  }' httpd.conf

Thanks! That worked great! I think I'm all set.