Variable in AWK

Question

How can I add a variable within awk command? below is my command:

cat /home/ubuntu/test/copy.txt | awk 'NR==21{print ".host = "$line";"}1' 

$line is basically an IP address which is retrieved from a text file. With the above command the output looks like

.host = ; 

Any immediate help would be really appreciated.

Format of copy.txt

backend default { #.host = value; need to be here .port = "8080"; } 

Answer 1

The variables in awk can be transferred from shell on this way:

awk -v variable=$line '..... 

and used inside on this way:

awk -v line1=$line 'NR==21 {print ".host = "line1";"}1' 

The variable should be set beforehand in bash so the things become:

line=192.168.0.10 awk -v line1=$line 'NR==21 {print ".host = "line1";"}1' /path/to/file ... 

Also you do not need cat, just use this way:

awk '....' /home/ubuntu/test/copy.txt 

To store the output in a file you should use something like:

awk '....' /home/ubuntu/test/copy.txt >/home/ubuntu/test/new_copy.txt 

and the result will be stored in /home/ubuntu/test/new_copy.txt