How to append a variable with dollar sign after a string match using sed?

Question

I have a variable with dollar signs in it:

ipvar_definitions="
var SSH_SERVERS \$HOME_NET
var FTP_SERVERS \$HOME_NET
var SIP_SERVERS \$HOME_NET
"

I want to append the value of this variable after a match using sed or perl or whatever one liner I can use.

When trying with sed using the code below:

sed   "/var SNMP_SERVERS/a ${ipvar_definitions}" /etc/snort.conf

I get this error:

sed: -e expression #1, char 24: expected newer version of sed

I get this error because my variable has dollar signs in it. I'd like to solve this in a one liner using sed, perl, awk or whatever I can use.

For clarification I am posting a sample input and the expected output:

Input:

# List of snmp servers on your network
var SNMP_SERVERS $HOME_NET

# Configure your service ports.  This allows snort to look for attacks destined

Expected output:

# List of snmp servers on your network
var SNMP_SERVERS $HOME_NET
var SSH_SERVERS $HOME_NET
var FTP_SERVERS $HOME_NET
var SIP_SERVERS $HOME_NET

# Configure your service ports.  This allows snort to look for attacks destined

The error probably comes from your sed version requiring a backslash before each literal newline you want to insert. — tripleee
– tripleee, Commented Dec 19, 2017 at 5:59

anubhava · Accepted Answer · 2016-09-09 14:28:44Z

2

Using gnu awk you can do this:

# no need to escape the $ if you use single quotes
ipvar_definitions='var SSH_SERVERS $HOME_NET
var FTP_SERVERS $HOME_NET
var SIP_SERVERS $HOME_NET'

# use awk command to insert ipvar_definitions after a line containing "var SNMP_SERVERS"
awk -v var="$ipvar_definitions" '1; /var SNMP_SERVERS/{print var}' /etc/snort.conf

Output:

# List of snmp servers on your network
var SNMP_SERVERS $HOME_NET
var SSH_SERVERS $HOME_NET
var FTP_SERVERS $HOME_NET
var SIP_SERVERS $HOME_NET

# Configure your service ports.  This allows snort to look for attacks destined

edited Sep 9, 2016 at 14:28

answered Sep 9, 2016 at 14:22

anubhava

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4 Comments

anubhava Over a year ago

To save output of this awk command in place use: awk -i inplace -v var="$ipvar_definitions" '1; /var SNMP_SERVERS/{print var}' /etc/snort.conf

Ed Morton Over a year ago

There's nothing gawk-specific about that command. It will become so if you add -i inplace of course but the OP doesn't seem to be asking for that.

anubhava Over a year ago

I mentioned gnu awk because my OSX awk didn't like multiline variable i.e -v var="$ipvar_definitions"

Ed Morton Over a year ago

Really? That's bizarre. I wonder if that's an OSX shell problem or an awk problem. I just tested with the default awk and GNU awk on OSX and it's an OSX awk problem as GNU awk works fine with it so the shell isn't having a problem with it. Weird...

Sundeep · Accepted Answer · 2017-12-19 05:22:12Z

0

$ export ipvar_definitions='
var SSH_SERVERS $HOME_NET
var FTP_SERVERS $HOME_NET
var SIP_SERVERS $HOME_NET
'

$ perl -pe 's/.*var SNMP_SERVERS.*/$&$ENV{ipvar_definitions}/' /etc/snort.conf 
# List of snmp servers on your network
var SNMP_SERVERS $HOME_NET
var SSH_SERVERS $HOME_NET
var FTP_SERVERS $HOME_NET
var SIP_SERVERS $HOME_NET


# Configure your service ports.  This allows snort to look for attacks destined

Further reading: https://perldoc.perl.org/Env.html

edited Dec 19, 2017 at 5:22

answered Sep 9, 2016 at 14:55

Sundeep

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