FileTest implements file test operations similar to those used in File::Stat. It exists as a standalone module, and its methods are also insinuated into the File class. (Note that this is not done by inclusion: the interpreter cheats).

Methods
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Instance Public methods
File.blockdev?(file_name) → true or false

Returns true if the named file is a block device.

file_name can be an IO object.

static VALUE
rb_file_blockdev_p(VALUE obj, VALUE fname)
{
#ifndef S_ISBLK
#   ifdef S_IFBLK
#       define S_ISBLK(m) (((m) & S_IFMT) == S_IFBLK)
#   else
#       define S_ISBLK(m) (0)  /* anytime false */
#   endif
#endif

#ifdef S_ISBLK
    struct stat st;

    if (rb_stat(fname, &st) < 0) return Qfalse;
    if (S_ISBLK(st.st_mode)) return Qtrue;

#endif
    return Qfalse;
}
File.chardev?(file_name) → true or false

Returns true if the named file is a character device.

file_name can be an IO object.

static VALUE
rb_file_chardev_p(VALUE obj, VALUE fname)
{
#ifndef S_ISCHR
#   define S_ISCHR(m) (((m) & S_IFMT) == S_IFCHR)
#endif

    struct stat st;

    if (rb_stat(fname, &st) < 0) return Qfalse;
    if (S_ISCHR(st.st_mode)) return Qtrue;

    return Qfalse;
}
File.directory?(file_name) → true or false

Returns true if the named file is a directory, or a symlink that points at a directory, and false otherwise.

file_name can be an IO object.

File.directory?(".")
VALUE
rb_file_directory_p(VALUE obj, VALUE fname)
{
#ifndef S_ISDIR
#   define S_ISDIR(m) (((m) & S_IFMT) == S_IFDIR)
#endif

    struct stat st;

    if (rb_stat(fname, &st) < 0) return Qfalse;
    if (S_ISDIR(st.st_mode)) return Qtrue;
    return Qfalse;
}
File.zero?(file_name) → true or false

Returns true if the named file exists and has a zero size.

file_name can be an IO object.

static VALUE
rb_file_zero_p(VALUE obj, VALUE fname)
{
    struct stat st;

    if (rb_stat(fname, &st) < 0) return Qfalse;
    if (st.st_size == 0) return Qtrue;
    return Qfalse;
}
File.executable?(file_name) → true or false

Returns true if the named file is executable by the effective user and group id of this process. See eaccess(3).

static VALUE
rb_file_executable_p(VALUE obj, VALUE fname)
{
    FilePathValue(fname);
    fname = rb_str_encode_ospath(fname);
    if (eaccess(StringValueCStr(fname), X_OK) < 0) return Qfalse;
    return Qtrue;
}
File.executable_real?(file_name) → true or false

Returns true if the named file is executable by the real user and group id of this process. See access(3).

static VALUE
rb_file_executable_real_p(VALUE obj, VALUE fname)
{
    FilePathValue(fname);
    fname = rb_str_encode_ospath(fname);
    if (access(StringValueCStr(fname), X_OK) < 0) return Qfalse;
    return Qtrue;
}
File.exist?(file_name) → true or false

Return true if the named file exists.

file_name can be an IO object.

“file exists” means that stat() or fstat() system call is successful.

static VALUE
rb_file_exist_p(VALUE obj, VALUE fname)
{
    struct stat st;

    if (rb_stat(fname, &st) < 0) return Qfalse;
    return Qtrue;
}
File.exists?(file_name) → true or false

Deprecated method. Don't use.

static VALUE
rb_file_exists_p(VALUE obj, VALUE fname)
{
    const char *s = "FileTest#";
    if (obj == rb_mFileTest) {
        s = "FileTest.";
    }
    else if (obj == rb_cFile ||
             (RB_TYPE_P(obj, T_CLASS) &&
              RTEST(rb_class_inherited_p(obj, rb_cFile)))) {
        s = "File.";
    }
    rb_warning("%sexists? is a deprecated name, use %sexist? instead", s, s);
    return rb_file_exist_p(obj, fname);
}
File.file?(file) → true or false

Returns true if the named file exists and is a regular file.

file can be an IO object.

If the file argument is a symbolic link, it will resolve the symbolic link and use the file referenced by the link.

static VALUE
rb_file_file_p(VALUE obj, VALUE fname)
{
    struct stat st;

    if (rb_stat(fname, &st) < 0) return Qfalse;
    if (S_ISREG(st.st_mode)) return Qtrue;
    return Qfalse;
}
File.grpowned?(file_name) → true or false

Returns true if the named file exists and the effective group id of the calling process is the owner of the file. Returns false on Windows.

file_name can be an IO object.

static VALUE
rb_file_grpowned_p(VALUE obj, VALUE fname)
{
#ifndef _WIN32
    struct stat st;

    if (rb_stat(fname, &st) < 0) return Qfalse;
    if (rb_group_member(st.st_gid)) return Qtrue;
#endif
    return Qfalse;
}
File.identical?(file_1, file_2) → true or false

Returns true if the named files are identical.

file_1 and file_2 can be an IO object.

open("a", "w") {}
p File.identical?("a", "a")      #=> true
p File.identical?("a", "./a")    #=> true
File.link("a", "b")
p File.identical?("a", "b")      #=> true
File.symlink("a", "c")
p File.identical?("a", "c")      #=> true
open("d", "w") {}
p File.identical?("a", "d")      #=> false
static VALUE
rb_file_identical_p(VALUE obj, VALUE fname1, VALUE fname2)
{
#ifndef _WIN32
    struct stat st1, st2;

    if (rb_stat(fname1, &st1) < 0) return Qfalse;
    if (rb_stat(fname2, &st2) < 0) return Qfalse;
    if (st1.st_dev != st2.st_dev) return Qfalse;
    if (st1.st_ino != st2.st_ino) return Qfalse;
    return Qtrue;
#else
    BY_HANDLE_FILE_INFORMATION st1, st2;
    HANDLE f1 = 0, f2 = 0;

    f1 = w32_io_info(&fname1, &st1);
    if (f1 == INVALID_HANDLE_VALUE) return Qfalse;
    if (f1) {
        struct w32_io_info_args arg;
        arg.fname = &fname2;
        arg.st = &st2;
        f2 = (HANDLE)rb_ensure(call_w32_io_info, (VALUE)&arg, close_handle, (VALUE)f1);
    }
    else {
        f2 = w32_io_info(&fname2, &st2);
    }
    if (f2 == INVALID_HANDLE_VALUE) return Qfalse;
    if (f2) CloseHandle(f2);

    if (st1.dwVolumeSerialNumber == st2.dwVolumeSerialNumber &&
        st1.nFileIndexHigh == st2.nFileIndexHigh &&
        st1.nFileIndexLow == st2.nFileIndexLow)
        return Qtrue;
    return Qfalse;
#endif
}
File.owned?(file_name) → true or false

Returns true if the named file exists and the effective used id of the calling process is the owner of the file.

file_name can be an IO object.

static VALUE
rb_file_owned_p(VALUE obj, VALUE fname)
{
    struct stat st;

    if (rb_stat(fname, &st) < 0) return Qfalse;
    if (st.st_uid == geteuid()) return Qtrue;
    return Qfalse;
}
File.pipe?(file_name) → true or false

Returns true if the named file is a pipe.

file_name can be an IO object.

static VALUE
rb_file_pipe_p(VALUE obj, VALUE fname)
{
#ifdef S_IFIFO
#  ifndef S_ISFIFO
#    define S_ISFIFO(m) (((m) & S_IFMT) == S_IFIFO)
#  endif

    struct stat st;

    if (rb_stat(fname, &st) < 0) return Qfalse;
    if (S_ISFIFO(st.st_mode)) return Qtrue;

#endif
    return Qfalse;
}
File.readable?(file_name) → true or false

Returns true if the named file is readable by the effective user and group id of this process. See eaccess(3).

static VALUE
rb_file_readable_p(VALUE obj, VALUE fname)
{
    FilePathValue(fname);
    fname = rb_str_encode_ospath(fname);
    if (eaccess(StringValueCStr(fname), R_OK) < 0) return Qfalse;
    return Qtrue;
}
File.readable_real?(file_name) → true or false

Returns true if the named file is readable by the real user and group id of this process. See access(3).

static VALUE
rb_file_readable_real_p(VALUE obj, VALUE fname)
{
    FilePathValue(fname);
    fname = rb_str_encode_ospath(fname);
    if (access(StringValueCStr(fname), R_OK) < 0) return Qfalse;
    return Qtrue;
}
File.setgid?(file_name) → true or false

Returns true if the named file has the setgid bit set.

static VALUE
rb_file_sgid_p(VALUE obj, VALUE fname)
{
#ifdef S_ISGID
    return check3rdbyte(fname, S_ISGID);
#else
    return Qfalse;
#endif
}
File.setuid?(file_name) → true or false

Returns true if the named file has the setuid bit set.

static VALUE
rb_file_suid_p(VALUE obj, VALUE fname)
{
#ifdef S_ISUID
    return check3rdbyte(fname, S_ISUID);
#else
    return Qfalse;
#endif
}
File.size(file_name) → integer

Returns the size of file_name.

file_name can be an IO object.

static VALUE
rb_file_s_size(VALUE klass, VALUE fname)
{
    struct stat st;

    if (rb_stat(fname, &st) < 0) {
        int e = errno;
        FilePathValue(fname);
        rb_syserr_fail_path(e, fname);
    }
    return OFFT2NUM(st.st_size);
}
File.size?(file_name) → Integer or nil

Returns nil if file_name doesn't exist or has zero size, the size of the file otherwise.

file_name can be an IO object.

static VALUE
rb_file_size_p(VALUE obj, VALUE fname)
{
    struct stat st;

    if (rb_stat(fname, &st) < 0) return Qnil;
    if (st.st_size == 0) return Qnil;
    return OFFT2NUM(st.st_size);
}
File.socket?(file_name) → true or false

Returns true if the named file is a socket.

file_name can be an IO object.

static VALUE
rb_file_socket_p(VALUE obj, VALUE fname)
{
#ifndef S_ISSOCK
#  ifdef _S_ISSOCK
#    define S_ISSOCK(m) _S_ISSOCK(m)
#  else
#    ifdef _S_IFSOCK
#      define S_ISSOCK(m) (((m) & S_IFMT) == _S_IFSOCK)
#    else
#      ifdef S_IFSOCK
#        define S_ISSOCK(m) (((m) & S_IFMT) == S_IFSOCK)
#      endif
#    endif
#  endif
#endif

#ifdef S_ISSOCK
    struct stat st;

    if (rb_stat(fname, &st) < 0) return Qfalse;
    if (S_ISSOCK(st.st_mode)) return Qtrue;

#endif
    return Qfalse;
}
File.sticky?(file_name) → true or false

Returns true if the named file has the sticky bit set.

static VALUE
rb_file_sticky_p(VALUE obj, VALUE fname)
{
#ifdef S_ISVTX
    return check3rdbyte(fname, S_ISVTX);
#else
    return Qnil;
#endif
}

Returns true if the named file is a symbolic link.

File.world_readable?(file_name) → integer or nil

If file_name is readable by others, returns an integer representing the file permission bits of file_name. Returns nil otherwise. The meaning of the bits is platform dependent; on Unix systems, see stat(2).

file_name can be an IO object.

File.world_readable?("/etc/passwd")           #=> 420
m = File.world_readable?("/etc/passwd")
sprintf("%o", m)                              #=> "644"
static VALUE
rb_file_world_readable_p(VALUE obj, VALUE fname)
{
#ifdef S_IROTH
    struct stat st;

    if (rb_stat(fname, &st) < 0) return Qnil;
    if ((st.st_mode & (S_IROTH)) == S_IROTH) {
        return UINT2NUM(st.st_mode & (S_IRUGO|S_IWUGO|S_IXUGO));
    }
#endif
    return Qnil;
}
File.world_writable?(file_name) → integer or nil

If file_name is writable by others, returns an integer representing the file permission bits of file_name. Returns nil otherwise. The meaning of the bits is platform dependent; on Unix systems, see stat(2).

file_name can be an IO object.

File.world_writable?("/tmp")                  #=> 511
m = File.world_writable?("/tmp")
sprintf("%o", m)                              #=> "777"
static VALUE
rb_file_world_writable_p(VALUE obj, VALUE fname)
{
#ifdef S_IWOTH
    struct stat st;

    if (rb_stat(fname, &st) < 0) return Qnil;
    if ((st.st_mode & (S_IWOTH)) == S_IWOTH) {
        return UINT2NUM(st.st_mode & (S_IRUGO|S_IWUGO|S_IXUGO));
    }
#endif
    return Qnil;
}
File.writable?(file_name) → true or false

Returns true if the named file is writable by the effective user and group id of this process. See eaccess(3).

static VALUE
rb_file_writable_p(VALUE obj, VALUE fname)
{
    FilePathValue(fname);
    fname = rb_str_encode_ospath(fname);
    if (eaccess(StringValueCStr(fname), W_OK) < 0) return Qfalse;
    return Qtrue;
}
File.writable_real?(file_name) → true or false

Returns true if the named file is writable by the real user and group id of this process. See access(3)

static VALUE
rb_file_writable_real_p(VALUE obj, VALUE fname)
{
    FilePathValue(fname);
    fname = rb_str_encode_ospath(fname);
    if (access(StringValueCStr(fname), W_OK) < 0) return Qfalse;
    return Qtrue;
}
File.zero?(file_name) → true or false

Returns true if the named file exists and has a zero size.

file_name can be an IO object.

static VALUE
rb_file_zero_p(VALUE obj, VALUE fname)
{
    struct stat st;

    if (rb_stat(fname, &st) < 0) return Qfalse;
    if (st.st_size == 0) return Qtrue;
    return Qfalse;
}