use strict;
use warnings;

my @insert1 =  qw(1 1 1);
my @insert2 =  qw(2 2 2);
my @inserts = (\@insert1, \@insert2);

my $outfile = 'delme.txt';
my $ins = 0;

open OUTFILE, '>', $outfile;
print OUTFILE <<DATA;
first second third
1 2 3
x y z
DATA
close OUTFILE;

for (@inserts) {
    insert (@$_);
    local @ARGV = $outfile;
    local $/ = undef;
    print <>;
}

...