sed + append new lines after matched word but ignore if lines are exists

we create the follwinmg sed line in order to add the lines after mached word ( on redhat 7.x machines )

sed -i '/\[Service\]/a MemoryAccounting=yes\nMemoryCurrent=8192000\nMemoryLimit=8192000' /lib/systemd/system/rsyslog.service

example of the file before update

cat /lib/systemd/system/rsyslog.service
[Unit]
Description=System Logging Service
;Requires=syslog.socket
Wants=network.target network-online.target
After=network.target network-online.target
Documentation=man:rsyslogd(8)
Documentation=http://www.rsyslog.com/doc/

[Service]
Type=notify
EnvironmentFile=-/etc/sysconfig/rsyslog
ExecStart=/usr/sbin/rsyslogd -n $SYSLOGD_OPTIONS
Restart=on-failure
UMask=0066
StandardOutput=null
Restart=on-failure

[Install]
WantedBy=multi-user.target
;Alias=syslog.service

example of the file after the update by sed

cat /lib/systemd/system/rsyslog.service
[Unit]
Description=System Logging Service
;Requires=syslog.socket
Wants=network.target network-online.target
After=network.target network-online.target
Documentation=man:rsyslogd(8)
Documentation=http://www.rsyslog.com/doc/

[Service]
MemoryAccounting=yes
MemoryCurrent=8192000
MemoryLimit=8192000
Type=notify
EnvironmentFile=-/etc/sysconfig/rsyslog
ExecStart=/usr/sbin/rsyslogd -n $SYSLOGD_OPTIONS
Restart=on-failure
UMask=0066
StandardOutput=null
Restart=on-failure

[Install]
WantedBy=multi-user.target
;Alias=syslog.service

now the problem is when we run again the sed line then we get duplicate lines as

[Service]
MemoryAccounting=yes
MemoryCurrent=8192000
MemoryLimit=8192000
MemoryAccounting=yes
MemoryCurrent=8192000
MemoryLimit=8192000

any suggestion how to ignore editing when the lines are already exists ?

notes:

in order to complete service update we need to do the following:

systemctl daemon-reload
systemctl restart rsyslog.service

This should work

sed -i.SAVED '/\[Service\]/N;
s/\n/ /;
/\[Service\] Type=notify/c\
[Service]\
MemoryAccounting=yes\
MemoryCurrent=8192000\
MemoryLimit=8192000\
Type=notify

/\[Service\] M.*/s/ /\n/
' /lib/systemd/system/rsyslog.service

it's joining lines using N, replacing the nl with space checking if it matches the original line.

Also saving the original file just in case.

Using sed

$ sed -Eei.bak '/\[service]/I{n;/^memoryaccounting/I!{i MemoryAccounting=yes\nMemoryCurrent=8192000\nMemoryLimit=8192000' -e '}}' input_file
[Unit]
Description=System Logging Service
;Requires=syslog.socket
Wants=network.target network-online.target
After=network.target network-online.target
Documentation=man:rsyslogd(8)
Documentation=http://www.rsyslog.com/doc/

[Service]
MemoryAccounting=yes
MemoryCurrent=8192000
MemoryLimit=8192000
Type=notify
EnvironmentFile=-/etc/sysconfig/rsyslog
ExecStart=/usr/sbin/rsyslogd -n $SYSLOGD_OPTIONS
Restart=on-failure
UMask=0066
StandardOutput=null
Restart=on-failure

[Install]
WantedBy=multi-user.target
;Alias=syslog.service

This sed command will skip the insertion of text if the [Service] is immediately followed by a line starting with MemoryAccounting=.

sed -i.orig '
/\[Service]/{
n
/^MemoryAccounting=/b
i\
MemoryAccounting=yes\
MemoryCurrent=8192000\
MemoryLimit=8192000
}' rsyslog.service