perl のファイルテスト演算子

-X FILEHANDLE
-X EXPR
-X A file test, where X is one of the letters listed below. This unary operator takes one argument, either a filename or a filehandle, and tests the associated file to see if something is true about it. If the argument is omitted, tests $_, except for
"-t", which tests STDIN. Unless otherwise documented, it returns 1 for true and '' for false, or the undefined value if the file doesn't exist. Despite the funny names, precedence is the same as any other named unary operator, and the argument may
be parenthesized like any other unary operator. The operator may be any of:

-r File is readable by effective uid/gid.
-w File is writable by effective uid/gid.
-x File is executable by effective uid/gid.
-o File is owned by effective uid.

-R File is readable by real uid/gid.
-W File is writable by real uid/gid.
-X File is executable by real uid/gid.
-O File is owned by real uid.

-e File exists.
-z File has zero size (is empty).
-s File has nonzero size (returns size in bytes).

-f File is a plain file.
-d File is a directory.
-l File is a symbolic link.
-p File is a named pipe (FIFO), or Filehandle is a pipe.
-S File is a socket.
-b File is a block special file.
-c File is a character special file.
-t Filehandle is opened to a tty.

-u File has setuid bit set.
-g File has setgid bit set.
-k File has sticky bit set.

-T File is an ASCII text file (heuristic guess).
-B File is a "binary" file (opposite of -T).

-M Script start time minus file modification time, in days.
-A Same for access time.
-C Same for inode change time (Unix, may differ for other platforms)