You'll have to define "merge". Without any particular algorithm this could be as simple as

If you get stuck with a particular point of your code, do ask again.

EDIT: of particular use might by readdir, open, and perlsyn.

Take a look at Join files using perl.

Regards, Karl

$ perl -pe '' a*.pl > out.txt
[download]

$ wc out.txt
 186  583 4219 out.txt

$ wc  a*.pl
  11   27  187 a.pl
  35  125  719 add2.pl
  11   47  305 analyse_fable.pl
  25   95  502 any.pl
  24   99  532 any2.pl
  24   55  357 aoh.pl
  56  139 1617 array_hash.pl
 186  587 4219 total
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open OUT,'>merged.txt' or die $!;
print OUT $_ foreach (<>);
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./a.pl /home/user/*.txt
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See Path::Tiny, File::Find::Rule

#!/usr/bin/perl --
use strict; use warnings;
use Path::Tiny qw/ path /;
use File::Find::Rule qw/ find /;
Main( @ARGV );
exit( 0 );
sub Main {
#~     MainReaddir( @_ );
    MainRule( @_ );
}
sub MainRule {
    my( $dir , $mergeinto ) = @_;
    my $mergefh = path( $mergeinto )->opena_utf8;
    my $readdir = path( $dir )->realpath;
    my @entries = find( 
        file     =>
        maxdepth => 1,
        name     => qr/\.txt$/,
        in       => $readdir,
    );
    for my $name ( @entries ){
        my $entry = path( $name );
        if( $entry->is_file and $name =~ /\.txt$/ ){
            my $inputfh = $entry->openr_utf8;
            Mergerations( $mergefh, $inputfh );
            close $inputfh;
        }
    }
    close $mergefh;
}
sub MainReaddir {
    my( $dir , $mergeinto ) = @_;
    my $mergefh = path( $mergeinto )->opena_utf8;
    my $readdir = path( $dir )->realpath
                        ->iterator( { qw/ recurse 0 / });
    while( my $entry = $readdir->() ){
        if( $entry->is_file and $entry =~ /\.txt$/ ){
            my $inputfh = path( $entry )->openr_utf8;
            Mergerations( $mergefh, $inputfh );
            close $inputfh;
        }
        
    }
}
sub Staterator {
    my( $out, $in ) = @_;
    ...
}
__END__
[download]

see perlintro, also chromatics free book Modern Perl a loose description of how experienced and effective Perl 5 programmers work....You can learn this too.
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