How can I pass variables from awk to a shell command?

You cannot grab the output of an awk system() call, you can only get the exit status. Use the getline/pipe or getline/variable/pipe constructs

awk '{
    cmd = "your_command " $1
    while (cmd | getline line) {
        do_something_with(line) 
    }
    close(cmd)
}' file

FYI here's how to use awk to process files whose names are stored in a file (providing wc-like functionality in this example):

gawk '
NR==FNR { ARGV[ARGC++]=$0; next }
{ nW+=NF; nC+=(length($0) + 1) }
ENDFILE { print FILENAME, FNR, nW, nC; nW=nC=0 }
' file

The above uses GNU awk for ENDFILE. With other awks just store the values in an array and print in a loop in the END section.

I would suggest another solution:

awk '{print $1}' myfile | xargs wc

the difference is that it executes wc once with multiple arguments. It often works (for example, with kill command)

Or use the pipe | as in bash then retrive the output in a variable with awk's getline, like this

 zcat /var/log/fail2ban.log* | gawk  '/.*Ban.*/  {print $7};' | sort | uniq -c | sort | gawk '{ "geoiplookup " $2 "| cut -f2 -d: " | getline geoip; print $2 "\t\t" $1 " " geoip}'

That line will print all the banned IPs from your server along with their origin (country) using the geoip-bin package.

The last part of that one-liner is the one that affects us :

gawk '{ "geoiplookup " $2 "| cut -f2 -d: " | getline geoip; print $2 "\t\t" $1 " " geoip}'

It simply says : run the command "geoiplookup 182.193.192.4 | -f2 -d:" ($2 gets substituted as you may guess) and put the result of that command in geoip (the | getline geoip bit). Next, print something something and anything inside the geoip variable.

The complete example and the results can be found here, an article I wrote.