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

you are close. you have to concatenate the command line with awk variables:

awk '{system("wc "$1)}' myfile

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.

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