Perl Pocket Reference, 5th Edition

File Test Operators

These unary operators take one argument, either a filename or a filehandle, and test the associated file to see if something is true about it. If the argument is omitted, they test $_ (except for -t, which tests STDIN). If the special argument _ (underscore) is passed, they use the information from the preceding test or stat call. File test operators can be stacked, e.g., -r -w -x file.

See also the filetest pragma in page 19.

-r -w -x	File is readable/writable/executable by effective uid/gid.
-R -W -X	File is readable/writable/executable by real uid/gid.
-o -O	File is owned by effective/real uid.
-e -z	File exists/has zero size.
-s	File exists and has nonzero size. Returns the size.
-f -d	File is a plain file/a directory.
-l -S -p	File is a symbolic link/a socket/a named pipe (FIFO).
-b -c	File is a block/character special file.
-u -g -k	File has setuid/setgid/sticky bit set.
-t	Filehandle (default STDIN) is opened to a tty.
-T -B	File is a text/nontext (binary) file. These tests return true on an empty file, or a file at EOF when testing a filehandle.
-M -A -C	Returns the modification/access/inode-change time of the file. The value is relative to the time the program started and expressed in fractional days. See also $^T in page 72.