use File::Find::Rule;

## GLOB
my @files = find( file => maxdepth => 1, name => '_*_.txt', in => $directory );

## REGEX
my @files = find( file => maxdepth => 1, name => qr/_.+?_\.txt$/, in => $directory );

## verbose
my @files = File::Find::Rule->file()
                            ->maxdepth(1) # do not recurse
                            ->name( '_*_.txt',  )
                            ->in( $directory  );

...