Replace a line if previous lines match-CodePudding

I'm trying to write a bash script but I'm currently stuck.

Let's say i have the following file:

targets {
        type = pppcfg_target_internet;
        name = "internet";
        only_crypt_auth = no;
        local {
                username = "";
                passwd = "";

I would like to replace the username and password. The problem is, this section exists multiple times, except for the second line.

So what I would like to do:

Replace "username" and "password" if there is a "type = pppcfg_target_internet;" a few lines before.

Preferably, I'd like to keep it flexible enough that I don't have to set it to the exact line in case the code changes a bit or a line gets added.

So "If there is "pppcfg_target_internet" in the 5-10 lines above the searched string, replace "password" and "username".

I will be glad to receive any help. Also for the recommendation whether to use "ask" or "sed".

CodePudding user response：

You can use sed to choose range of text between specific lines where you want to replace, like the following

sed '/pppcfg_target_internet/,/}/s/passwd.*/passwd = "newpass"/g'

This means, that between strings with "pppcfg_target_internet" and "}" find and replace string starting with passwd with the next string: 'passwd = "newpass"'

Maybe it would be good to create some unique block ending

CodePudding user response：

This might work for you (GNU sed):

sed -E '/type = pppcfg_target_internet;/{:a;N;/passwd/!ba
        s/(username = ).*/\1"new user";/m;s/(passwd = ).*/\1"new pass";/m}' file

Gather up lines between type = pppcfg_target_internet; and passwd and then substitute new user and password values.

N.B. The use of the m flag on the substitute command to assure the substitution only occurs for that matching line.