bash/sed - adding multiple lines at specific location in file-CodePudding

I want to automate adding new backends to a configuration file and can't figure out how to do it. The relevant part of the file looks like this:

[backend]
backends = backend-1 backend-2
timeout = 10
connectionsperhost = 100

[backend-1]
url = https://somedomain.com
secret = 6135bcb7849ca1886e2de193

[backend-2]
url = https://anotherdomain.com
secret = 75048ad646a5af787cbbaaa3

I'm looking for a simple solution to add another backend entry with a specific url and secret.

[backend-3]
url = https://adiffrentdomain.com
secret = 42349234238423424

and at the same time append the name "backend-3" to the line "backends = " at the "[backend]" section.

Is there a way to make this work with sed or bash scripting in genereal?

kindly appreciate any help or hints!

CodePudding user response：

With awk for an arbitrary new backend entry with newbackendname, url and secret being the only provided inputs. Simply adds the new backend to the backends =-list and the corresponging block directly after the general [backend]-block.

awk -vnewentry="newbackendname" -vurl="http://new.url" -vsecret="secret123" '
  #in backends= line: add new entry (at first position)
  #and set `add` marker
  /^backends =/{sub(/^backends = /,"&"newentry" ",$0) ; add=1}
  #marker exists and empty line (end of header block) is found:
  #print new entry and unset marker `add`
  add && /^$/{ print "\n["newentry"]"
               print "url = "url
               print "secret = "secret
               add=0}
  #print by default
  1' infile.txt

Hopefully the comments make it easy to follow. With this code, you may as well just add url and secret via shell variables as awk -vurl="$URL" -vsecret="$SECRET" -vnewentry="$NEWBACKEND" '...' infile.txt

CodePudding user response：

Using sed

$ sed '/backends =/s/$/ backend-3/;/^\[backend-2/{N;N;s|secret.*|&\n\n[backend-3] \
url = https://adifferentdomain.com \
secret = 42349234238423424|}' input_file
[backend]
backends = backend-1 backend-2 backend-3
timeout = 10
connectionsperhost = 100

[backend-1]
url = https://somedomain.com
secret = 6135bcb7849ca1886e2de193

[backend-2]
url = https://anotherdomain.com
secret = 75048ad646a5af787cbbaaa3

[backend-3]
url = https://adiffrentdomain.com
secret = 42349234238423424

If the input is coming from variables, you would want to use double quotes instead to expand the variables. E.g;

sed "/backends =/s/$/ backend-3/;$a\\n[backend-3] \
url = $url_input \
secret = $secret_input" input_file

CodePudding user response：

You can try an approach with awk. It adds a backends entry to lines starting with backends and attaches a [backend-x] section with the given info after the last line of the [backend] block (after connectionsperhost).
Obviously it relies on the entries of the backends being correct since it doesn't count the [backend] sections individually.

url="www.domain.com"
s=9283283h4923h42934

% awk -v url="${url}" -v s="${s}" '/^backends/{x=NF-1; $0=$0" backend-"x} 
    /^connectionsperhost/{ print; $0="\n[backend-"x"]\nurl = "url"\nsecret = "s} 
    {print}' file
[backend]
backends = backend-1 backend-2 backend-3
timeout = 10
connectionsperhost = 100

[backend-3]
url = www.domain.com
secret = 9283283h4923h42934

[backend-1]
url = https://somedomain.com
secret = 6135bcb7849ca1886e2de193

[backend-2]
url = https://anotherdomain.com
secret = 75048ad646a5af787cbbaaa3

Data

cat file
[backend]
backends = backend-1 backend-2
timeout = 10
connectionsperhost = 100

[backend-1]
url = https://somedomain.com
secret = 6135bcb7849ca1886e2de193

[backend-2]
url = https://anotherdomain.com
secret = 75048ad646a5af787cbbaaa3