Appending a line to a file ONLY if it doesnt already exist. Using Sed?

Question

Hi I need to add the following line to the end of a config file:

include "/configs/projectname.conf"

to a file called lighttpd.conf

I am looking into using sed to do this, but i cant work out how to only insert it if the line doesnt already exist. Is anyone able to enlighten me?

Thanks in advance,

Ben

Answer 1

Just keep it simple :)

grep + echo should suffice:

grep -q 'include "/configs/projectname.conf"' foo.bar || echo 'include "/configs/projectname.conf"' >> foo.bar

Answer 2

use awk

awk 'FNR==NR && /configs.*projectname\.conf/{f=1;next}f==0;END{ if(!f) { print "your line"}} ' file file

Answer 3

Here's a sed version:

sed -e '\|include "/configs/projectname.conf"|h; ${x;s/incl//;{g;t};a\' -e 'include "/configs/projectname.conf"' -e '}' file

If your string is in a variable:

string='include "/configs/projectname.conf"'
sed -e "\|$string|h; \${x;s|$string||;{g;t};a\\" -e "$string" -e "}" file