Actually, it does work. Here's the source data in file.csv:

a;b;1;foo
j;k;2;dog
m;n;3;cat
y;z;1;bar
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And here's the script, which I have called at.pl:

#!/usr/bin/perl -w

use strict;
use warnings;

my @rows = `awk -F';' '\$3==1' file.csv`;
my $lines= join('', @rows );
print "string: $lines";
exit;
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and here's the output from running ./at.pl:

$ ./at.pl 
string: a;b;1;foo
y;z;1;bar
$
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awk is gawk 4.0.0, perl is 5.14.2. I still don't recommend doing it this way for reasons of efficiency and external dependency but it does give the right output.