cat data.txt | prog1.pl | prog2.pl option | prog3.pl > out.txt

##</code><code>##

# input file
good1
good2
bad1
good3

# expected output
good1
good2
good3

##</code><code>##

my %testdata = (
                 'good1' => 'good1',
                 'good2' => 'good2',
                 'bad1' => '',
                 'good3' => 'good3',
               );

##</code><code>##

my ($args = <<'ARGS')=~s/^\s+//gm;
arg1
ARGS

my ($input = <<'INPUT')=~s/^\s+//gm;
good1
good2
bad1
good3
INPUT

my ($expected_output = <<'OUTPUT')=~s/^\s+//gm;
good1
good2
good3
OUTPUT