#!/usr/bin/perl

use strict;  # you really should!

( @ARGV == 1 and -d $ARGV[0] ) or die "Usage: $0 dir_name > out.csv\n";

my $dirname = shift;
opendir( DIR, $dirname ) or die "$dirname: $!";

my @files = grep /.+\.txt$/, readdir DIR;
for my $file ( @files ) {
    my ( $basename ) = ( $file =~ /(.+)\.txt$/ );
    if ( open( F, $file )) {
        my ( $date, @lines ) = <F>;
        chomp $date;
        chomp @lines;
        print join( ",", "sourcefile", $basename, "date", $date, @lines ), "\n";
        close F;
    }
    else {
        warn "$file: $!\n";
    }
}