-X EXPR
-X
-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.
-s File has non-zero size (returns size).
-f File is a plain file.
-d File is a directory.
-l File is a symbolic link.
-p File is a named pipe (FIFO).
-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 a text file.
-B File is a binary file (opposite of -T).
-M Age of file in days when script started.
-A Same for access time.
-C Same for inode change time.
The interpretation of the file permission operators -r, -R, -w,
-W, -x, and -X is based solely on the mode of the file and the uids and gids of the user.
There may be other reasons you can't actually read, write or execute the
file. Also note that, for the superuser,
-r, -R, -w, and -W always return 1, and -x and -X return 1 if any execute bit is set in the mode. Scripts run by the
superuser may thus need to do a stat to determine the actual
mode of the file, or temporarily set the uid to something else.
Example:
while (<>) {
chop;
next unless -f $_; # ignore specials
...
}
Note that -s/a/b/ does not do a negated substitution. Saying
-exp still works as expected, however--only single letters following a minus are
interpreted as file tests.
The -T and -B switches work as follows. The first block or so of the file is examined for
odd characters such as strange control codes or characters with the high
bit set. If too many odd characters (>30%) are found, it's a -B file, otherwise it's a -T file. Also, any file containing null in the first block is considered a
binary file. If -T
or -B is used on a filehandle, the current stdio buffer is examined rather than
the first block. Both -T and -B return
TRUE on a null file, or a file at
EOF when testing a filehandle. Because you have to read a file to do the
-T test, on most occasions you want to use a -f
against the file first, as in next unless -f $file && -T $file.
If any of the file tests (or either the stat or
lstat operators) are given the special filehandle consisting
of a solitary underline, then the stat structure of the previous file test
(or stat operator) is used, saving a system call. (This doesn't work with -t, and you need to remember that lstat and -l will leave values in the stat structure for the symbolic link, not the real
file.) Example:
print "Can do.\n" if -r $a || -w _ || -x _;
stat($filename);
print "Readable\n" if -r _;
print "Writable\n" if -w _;
print "Executable\n" if -x _;
print "Setuid\n" if -u _;
print "Setgid\n" if -g _;
print "Sticky\n" if -k _;
print "Text\n" if -T _;
print "Binary\n" if -B _;