™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.
™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() in order to determine the actual mode of the
file, or temporarily set the uid to something else.
Example:
while (<>) {
chop;
next unless ™f $_; # ignore specials
...
}
Note that ™s/a/b/ does not do a negated substitution. Saying
™exp($foo) 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.
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 _;
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