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 returns1 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:
-rFile is readable by effective uid/gid.-wFile is writable by effective uid/gid.-xFile is executable by effective uid/gid.-oFile is owned by effective uid.-RFile is readable by real uid/gid.-WFile is writable by real uid/gid.-XFile is executable by real uid/gid.-OFile is owned by real uid.-eFile exists.-zFile has zero size (is empty).-sFile has nonzero size (returns size in bytes).-fFile is a plain file.-dFile is a directory.-lFile is a symbolic link.-pFile is a named pipe (FIFO), or Filehandle is a pipe.-SFile is a socket.-bFile is a block special file.-cFile is a character special file.-tFilehandle is opened to a tty.-uFile has setuid bit set.-gFile has setgid bit set.-kFile has sticky bit set.-TFile is an ASCII text file (heuristic guess).-BFile is a "binary" file (opposite of -T).-MScript start time minus file modification time, in days.-ASame for access time.-CSame for inode change time (Unix, may differ for other platforms)Example:
while (<>) {chomp;next unless -f $_;# ignore specials#... }The interpretation of the file permission operators-r,-R,-w,-W,-x, and-X is by default based solely on the mode of the file and the uids and gids of the user. There may be other reasons you can't actually read, write, or execute the file. Such reasons may be for example network filesystem access controls, ACLs (access control lists), read-only filesystems, and unrecognized executable formats.
Also note that, for the superuser on the local filesystems, the-r,-R,-w, and-W tests always return 1, and-x and-X return 1 if any execute bit is set in the mode. Scripts run by the superuser may thus need to do a stat() to determine the actual mode of the file, or temporarily set their effective uid to something else.
If you are using ACLs, there is a pragma calledfiletest that may produce more accurate results than the bare stat() mode bits. When under theuse filetest 'access' the above-mentioned filetests will test whether the permission can (not) be granted using the access() family of system calls. Also note that the-x and-X may under this pragma return true even if there are no execute permission bits set (nor any extra execute permission ACLs). This strangeness is due to the underlying system calls' definitions. Read the documentation for thefiletest pragma for more information.
Note that-s/a/b/ does not do a negated substitution. Saying-exp($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 strange 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 IO 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 innext unless -f $file && -T $file.
If any of the file tests (or either thestat orlstat 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.) (Also, if the stat buffer was filled by anlstat call,-T and-B will reset it with the results ofstat _). 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 _;Perldoc Browser is maintained by Dan Book (DBOOK). Please contact him via theGitHub issue tracker oremail regarding any issues with the site itself, search, or rendering of documentation.
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