• Java

long x = new File(path).length();

• Ada

X : constant File_Size := Size (Path);

• C

struct stat st;
if (stat (path &st) == 0) x = st.st_size;

• C

FILE *f = fopen(path, "rb");
fseek(f, 0, SEEK_END);
int x = ftell(f);
fclose(f);

• C++

std::ifstream f(path, std::ios::in | std::ios::binary);
f.seekg(0, std::ios::end);
size_t x = f.tellg();

• C#

var filePath = "Sample.txt";
var fileInfo = new FileInfo(filePath);
var _x = fileInfo.Length;

• C#

long? FileSize(string path) {
    if (!File.Exists(path)) {
        return null;
    }
    return (new FileInfo(filePath)).Length;
}

• D

auto x = getSize(path);

• Dart

var x = File(path).lengthSync();

• Dart

final x = (await File(path).readAsBytes()).length;

• Elixir

def main(path) do
  _x =
    path
    |> File.stat!()
    |> Map.get(:size)
end

• Fortran

program xx
implicit none
character(len=256) :: message
character(len=4096) :: filename
integer :: ios,x
logical :: foundit
filename='myfile'
inquire(file=filename,exist=foundit,size=x,iostat=ios,iomsg=message)
if(.not.foundit)then
   write(*,*)'file ',trim(filename),' not found'
elseif(ios.ne.0)then
   write(*,*)trim(message)
else
   write(*,*)'size =',x,'bytes'
endif
end program xx

• Go

info, err := os.Stat(path)
if err != nil {
	return err
}
x := info.Size()

• Haskell

filesize = withFile path ReadMode hFileSize

• JS

let x = read(path).length

• Lisp

(defvar x (osicat-posix:stat-size (osicat-posix:stat #P"path")))

• PHP

$x = filesize($path);

• Pascal

x := filesize(path);

• Perl

my $x = -s $path;

• Python

x = os.path.getsize(path)

• Ruby

x = File.size(path)

• Rust

let x = path.metadata()?.len();

• Rust

let x = fs::metadata(path)?.len();

• Rust

let x = fs::metadata(path)?.st_size();