How to use awk variables in regular expressions?

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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?

awk regex
5 Answers

The problem of the answers above is that you cannot use the "metacharacters" (e.g. \< for a word boundary at the beginning of a word) if you use a string instead of a regular expression /.../. If you had a domain xyz.com and two sites ab.xyz.com and cd.prefix_xyz.com, the numbers of the two site entries would be added to xyz.com

Here's a solution using awk's pipe and the sed command: ...

for(dom in domain) {
    while(getline < "./site" > 0) {
        # let sed replaces occurence of the domain at the end of the site
        cmd = "echo '" $1 "' | sed 's/\\<'" dom "'$/NO_VALID_DOM/'"
        cmd | getline x
        close(cmd)
        if (match(x, "NO_VALID_DOM")) { 
          domain[dom]+=$2;
        }
    }
    close("./site") # this misses in original code
}

...

user_66950390
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