How to insert lines after second pattern with linux sed command - linux

Question

I want to insert this block:
host client3 {
hardware ethernet c0:03:03:bc:30:fa;
}
after this block:
subnet 11.10.0.0 netmask 255.255.255.0 {
range 11.10.1.2 11.10.1.254;
group {
filename "10M-5M-OKS2016NOV.cm";
The line: filename "10M-5M-OKS2016NOV.cm";
apears multiple times in the file. But only once inside subnet 11.10.0.0 netmask 255.255.255.0 {
Until now I can print the subnet block until the "filename":
sed -n -e :a -e '/subnet 11\.10\.0\.0 netmask 255\.255\.255\.0/,/}/{/filename "10M-5M-OKS2016NOV\.cm";/!{$!{N;ba};};p;}' dhcpd.conf
but when I try:
sed -n -e :a -e '/subnet 11\.10\.0\.0 netmask 255\.255\.255\.0/,/}/{/filename "10M-5M-OKS2016NOV\.cm";/!{$!{N;ba};};a\ \thost client3 {\n\thardware ethernet c0:03:03:bc:30:fa;\n\t}\n;}' dhcpd.conf
I get:
sed: -e expression #1, char 0: unmatched `{'
subnet 10.10.0.0 netmask 255.255.255.0 {
range 10.10.0.2 10.10.0.254;
group {
filename "10M-5M-OKS2016NOV.cm";
host client1 {
hardware ethernet a0:b4:3d:bc:df:fa;
}
host client2 {
hardware ethernet 90:6e:bb:ba:cd:d4;
}
}
}
subnet 11.10.0.0 netmask 255.255.255.0 {
range 11.10.1.2 11.10.1.254;
group {
filename "10M-5M-OKS2016NOV.cm";
host client1 {
hardware ethernet c0:14:e3:bc:df:fa;
}
host client2 {
hardware ethernet 90:6e:fb:ba:3d:04;
}
}
}
subnet 12.10.0.0 netmask 255.255.255.0 {
range 12.10.2.2 12.10.2.254;
group {
filename "10M-5M-OKS2016NOV.cm";
host client1 {
hardware ethernet c0:a4:3d:bc:df:fa;
}
host client2 {
hardware ethernet 90:6e:bb:ca:3d:04;
}
}
}

Answer 1

Please try something like:
#!/bin/bash
# define newline and tab characters for replacement
NL=$'\n'
NL="\\$NL"
TAB=$'\t'
TAB="\\$TAB"
sed '
:l
N
$!b l
# first of all slurp all lines in the pattern space
# and perform the replacement over the lines
s/subnet 11\.10\.0\.0 netmask 255\.255\.255\.0[^}]*filename "10M-5M-OKS2016NOV\.cm";/&'"$NL$TAB"'host client3 {'"$NL$TAB$TAB"'hardware ethernet c0:03:03:bc:30:fa;'"$NL$TAB"'}/g
' dhcpd.conf
It yields the following output by using the posted lines as dhcpd.conf,
subnet 10.10.0.0 netmask 255.255.255.0 {
range 10.10.0.2 10.10.0.254;
group {
filename "10M-5M-OKS2016NOV.cm";
host client1 {
hardware ethernet a0:b4:3d:bc:df:fa;
}
host client2 {
hardware ethernet 90:6e:bb:ba:cd:d4;
}
}
}
subnet 11.10.0.0 netmask 255.255.255.0 {
range 11.10.1.2 11.10.1.254;
group {
filename "10M-5M-OKS2016NOV.cm";
host client3 {
hardware ethernet c0:03:03:bc:30:fa;
}
host client1 {
hardware ethernet c0:14:e3:bc:df:fa;
}
host client2 {
hardware ethernet 90:6e:fb:ba:3d:04;
}
}
}
subnet 12.10.0.0 netmask 255.255.255.0 {
range 12.10.2.2 12.10.2.254;
group {
filename "10M-5M-OKS2016NOV.cm";
host client1 {
hardware ethernet c0:a4:3d:bc:df:fa;
}
host client2 {
hardware ethernet 90:6e:bb:ca:3d:04;
}
}
}
It initially slurps all the lines at first to process multi lines efficiently.
It assumes the right curly brace } does not appear in the search target block
to achieve the shortest match in regex.
Hope this helps.

Answer 2

This might work for you (GNU sed):
sed '/subnet 11\.10\.0\.0 netmask 255\.255\.255\.0/{:a;n;/filename "10M-5M-OKS2016NOV\.cm";/!ba;p;s/\S.*/host client3 {/p;s// hardware ethernet c0:03:03:bc:30:fa;/p;s//}/}' file
This finds the first line containing subnet 11.10.0.0 netmask 255.255.255.0 and then reads on further until the line containing filename "10M-5M-OKS2016NOV.cm";. After printing that line it uses the line as a template to format the required detail.
Another solution, using a preformed insertion file:
cat <<\! | sed '/subnet 11\.10\.0\.0 netmask 255\.255\.255\.0/!b;:a;n;/filename "10M-5M-OKS2016NOV\.cm";/!ba;r /dev/stdin' file
host client3 {
hardware ethernet c0:03:03:bc:30:fa;
}
!

Answer 3

sed is great as a stream editor, that means to process multiple times the same actions. Here you just want to insert once a bloc of text. That would be much simpler (more readable and maintenable) with ed:
ed dhcpd.conf <<EOF
/subnet 11.10.0.0/
/filename/
a
host client3 {
hardware ethernet c0:03:03:bc:30:fa;
}
.
w
q
EOF
Beware: ed is a file editor. That means that the dhcpd.conf file will be changed by the above script. Make sure to have a backup if things goes wrong...