How to use awk variables in regular expressions?

Question

I have a file called domain which contains some domains. For example:

google.com facebook.com ... yahoo.com 

And I have another file called site which contains some sites URLs and numbers. For example:

image.google.com   10 map.google.com     8 ... photo.facebook.com  22 game.facebook.com   15 .. 

Now I'm going to count the url number each domain has. For example: google.com has 10+8. So I wrote an awk script like this:

BEGIN{   while(getline dom < "./domain" > 0) {     domain[dom]=0;   }   for(dom in domain) {     while(getline < "./site" > 0) {       if($1 ~/$dom$)   #if $1 end with $dom {         domain[dom]+=$2;       }     }   } } 

But the code if($1 ~/$dom$) doesn't run like I want. Because the variable $dom in the regular expression was explained literally. So, the first question is:

Is there any way to use variable $dom in a regular expression?

Then, as I'm new to writing script

Is there any better way to solve the problem I have?

Answer 1

awk can match against a variable if you don't use the // regex markers.

if ( $0 ~ regex ){ print $0; }

In this case, build up the required regex as a string

regex = dom"$" 

Then match against the regex variable

if ( $1 ~ regex ) {   domain[dom]+=$2; } 

Answer 2

First of all, the variable is dom not $dom -- consider $ as an operator to extract the value of the column number stored in the variable dom

Secondly, awk will not interpolate what's between // -- that is just a string in there.

You want the match() function where the 2nd argument can be a string that is treated as the regular expression:

if (match($1, dom "$")) {...} 

I would code a solution like:

awk '   FNR == NR {domain[$1] = 0; next}   {     for (dom in domain) {       if (match($1, dom "$")) {         domain[dom] += $2         break       }     }   }   END {for (dom in domain) {print dom, domain[dom]}} ' domain site