I want to write a program to change systems ip address from dhcp/static to static only. my original file’s contents will be either this
some initial text [ipv6] method=auto [ipv4] method=static dns=8.8.8.8; addresses1=192.168.1.10;24;192.168.1.1;
or it may be like this,
some initial text [ipv6] method=auto [ipv4] method=auto
Now, i want to change after [ipv4] pattern, so that after editing my file should looks like this
some initial text [ipv6] method=auto [ipv4] method=static dns=8.8.8.8;4.4.4.4; addresses1=192.168.1.20;24;192.168.1.1;
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Answer
Here’s a Perl solution. It sets the record delimiter to 2 newlines, so paragraphs are read. If the paragraph contains [ipv4], replace the input with the replacement. Replace data with the name of your file, or with "$@" and make it into a shell script. Add -i as an option to Perl if you want to overwrite files (don’t do that until you’ve tested it).
perl -pe '
my $replacement = qq"[ipv4]n" .
"method=staticn" .
"dns=8.8.8.8;4.4.4.4;n" .
"addresses1=192.168.1.20;24;192.168.1.1;nn";
$/ = "nn";
$_ = $replacement if (m/^[ipv4]$/m);' data
There are many alternative ways of writing that code; I make no claims other than “it works for me”.
Given the text of your question as the input, the output is:
I want to write a program to change systems ip address from dhcp/static to static only. my original file's contents will be either this some initial text [ipv6] method=auto [ipv4] method=static dns=8.8.8.8;4.4.4.4; addresses1=192.168.1.20;24;192.168.1.1; or it may be like this, some initial text [ipv6] method=auto [ipv4] method=static dns=8.8.8.8;4.4.4.4; addresses1=192.168.1.20;24;192.168.1.1; Now, i want to change after [ipv4] pattern, so that after editing my file should looks like this some initial text [ipv6] method=auto [ipv4] method=static dns=8.8.8.8;4.4.4.4; addresses1=192.168.1.20;24;192.168.1.1;