For file operations: Path::Tiny

use strict; use warnings; use feature 'say';
use Path::Tiny qw/ path /;

say qx# ls /tmp/*.txt #;

my $dir   = '/tmp/';
my $ext   = '.txt';
my $regex = qr/$ext/;

my @paths = path( $dir )->children( $regex );

for my $file ( @paths ) {
    my $name    = path( $file )->basename( $regex );
    my $newname = join '', reverse split '', $name;

    path( $file )->move( join '', $dir, $newname, $ext );
}

say qx# ls /tmp/*.txt #;

__END__
[download]

Output:

/tmp/bar.txt
/tmp/foo.txt

/tmp/oof.txt
/tmp/rab.txt
[download]

Hope this helps!