Parenthesised matches always end up in the match variables $1, $2, ..., so you could write:

while (<CONFIG_FILE>) {
 if (/^frz\s+=\s+(\w+);/) {$bar=$1}
}
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If you have more than one pair of parenthesis, $1 will refer to the match of the first pair, $2 to the second and so on. The pairs are ordered from left to right, counting their opening parenthesis, so:

"abc123def"=~/([a-z]+(\d+)(.*))/;
print "first: $1\nsecond: $2\nthird: $3\n";
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first: abc123def
second: 123
third: def

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        dakkar - Mobilis in mobile