regex in sed to replace particular string-CodePudding

I have a file config.txt which consist of lines like below

$ cat config.txt | head -n 3
[email protected]:26601
[email protected]:26604
[email protected]:26607

$ cat ip.txt | head -n 3
10.0.4.5
10.3.5.6
10.3.5.8

I would like to replace the IP address on config.txt with ip's on ip.txt file respectively

the expected output is

[email protected]:26601
[email protected]:26604
[email protected]:26607

Since the ip's in config file are dynamic, I need to use regex in sed to replace the IP. for an example:

$ echo "[email protected]:26601" | sed "s/*@\ :*/*@10.0.4.5:*/g"

but its not updating the ip's. I am very new to the regex in scripting. Kindly help!

CodePudding user response：

Well, in this case it is possible to use sed and a regex. You could first join the files and then use regex to shuffle lines:

paste config.txt ip.txt | sed 's/@[^:]*\(.*\)\t\(.*\)/@\2\1/'

Note that sed works in the context of a single line only. But a regex is not "dynamic", if the ip's in config file are dynamic then you should use something "more" then regex, better a full programming language with support for maps and internal state, like awk but also perl or python.

CodePudding user response：

A way using awk instead. It first reads ip.txt and stores its contents in an array indexed by line number, and then for each line of config.txt, replaces the IP address in it with the one from the corresponding line of ip.txt:

$ awk 'FNR==NR { ips[FNR] = $0; next }
       { sub(/@[^:] :/, "@" ips[FNR] ":"); print }' ip.txt config.txt
[email protected]:26601
[email protected]:26604
[email protected]:26607