I need to modify an ntp configuration file by adding some options to the line containing Ip addresses. I have been trying it for so long using sed command, but no able to modify the line unless i don’t know the IP addresses. Let say, i have few lines as, server 172.0.0.1 server 10.0.0.1
I need to add iburst option after the ip address.
I have tried command like.. sed -e 's/(d{1,3}.d{1.3}.d{1,3}.d{1,3})/ 1 iburst/g' ntp_file
or sed -e 's/^server +d{1,3}.d{1,3}.d{1,3}.d{1,3}/server 1.2.3 iburst/g' ntp_file
but its not modifying the line. Any kind of suggestions would be really appriciated.
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Answer
The regex you have used as POSIX BRE cannot match the expected strings due to d shorthand class that sed does not support, the misused dot inside a range quantifier and incorrect escaping of grouping and range quantifier delimiters.
You may use
sed -E -i 's/[0-9]{1,3}(.[0-9]{1,3}){3}/ & iburst/g' ntp_file
The POSIX ERE (enabled with the -E option) expression means to match
[0-9]{1,3}– one to three digits(.[0-9]{1,3}){3}– three occurrences of a dot and one to three digits
The replacement pattern is & iburst where & stands for the whole match.
The g flag replaces all occurrences.