use warnings;
use strict;

my @labels = qw/ foo bar quz /;

my %fh;
for my $label (@labels) {
    my $filename = "out_${label}.txt";
    open $fh{$label}, '>', $filename or die "$filename: $!";
}

while (<DATA>) {
    # or whatever condition you like, just a demo here
    if (/lbl_(foo|bar|quz)/) {
        print { $fh{$1} } $_; # how to print to one of these handles
    }
    else { print $_ } # just a default action, adjust as needed
}

close $_ for values %fh;

__DATA__
Hello lbl_foo
lbl_bar World
Test lbl_quz
lbl_foo A
No label here
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