NAME
Raku port of Perl's -X built-ins
SYNOPSIS
use P5-X; # exports -r -w -x -e -d -f -l -s -z
DESCRIPTION
This module tries to mimic the behaviour of Perl's -X built-ins as closely as possible in the Raku Programming Language.
ORIGINAL PERL 5 DOCUMENTATION
-X FILEHANDLE
-X EXPR
-X DIRHANDLE
-X A file test, where X is one of the letters listed below. This
unary operator takes one argument, either a filename, a
filehandle, or a dirhandle, 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. If the file
doesn't exist or can't be examined, it returns "undef" and sets
$! (errno). With the exception of the "-l" test they all follow
symbolic links because they use "stat()" and not "lstat()" (so
dangling symlinks can't be examined and will therefore report
failure).
Despite the funny names, precedence is the same as any other
named 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 (false if symlinks aren't
supported by the file system).
-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 or UTF-8 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)
Example:
while (<>) {
chomp;
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.
These operators are exempt from the "looks like a function rule"
described above. That is, an opening parenthesis after the
operator does not affect how much of the following code
constitutes the argument. Put the opening parentheses before the
operator to separate it from code that follows (this applies
only to operators with higher precedence than unary operators,
of course):
-s($file) + 1024 # probably wrong; same as -s($file + 1024)
(-s $file) + 1024 # correct
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: for example network filesystem access controls, ACLs
(access control lists), read-only filesystems, and unrecognized
executable formats. Note that the use of these six specific
operators to verify if some operation is possible is usually a
mistake, because it may be open to race conditions.
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 called "filetest" that
may produce more accurate results than the bare "stat" mode
bits. When under "use filetest 'access'", the above-mentioned
filetests test whether the permission can(not) be granted using
the access(2) family of system calls. Also note that the "-x"
and "-X" tests 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. Note also that, due to the
implementation of "use filetest 'access'", the "_" special
filehandle won't cache the results of the file tests when this
pragma is in effect. Read the documentation for the "filetest"
pragma for more information.
The "-T" and "-B" tests work as follows. The first block or so
of the file is examined to see if it is valid UTF-8 that
includes non-ASCII characters. If so, it's a "-T" file.
Otherwise, that same portion of the file is examined for odd
characters such as strange control codes or characters with the
high bit set. If more than a third of the characters are
strange, it's a "-B" file; otherwise it's a "-T" file. Also, any
file containing a zero byte in the examined portion is
considered a binary file. (If executed within the scope of a
use locale which includes "LC_CTYPE", odd characters are
anything that isn't a printable nor space in the current
locale.) 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 an empty 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"
operator) is 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" leave values in the stat structure for the symbolic
link, not the real file.) (Also, if the stat buffer was filled
by an "lstat" call, "-T" and "-B" will reset it with the results
of "stat _"). 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 _;
As of Perl 5.10.0, as a form of purely syntactic sugar, you can
stack file test operators, in a way that "-f -w -x $file" is
equivalent to "-x $file && -w _ && -f _". (This is only fancy
syntax: if you use the return value of "-f $file" as an argument
to another filetest operator, no special magic will happen.)
Portability issues: "-X" in perlport.
To avoid confusing would-be users of your code with mysterious
syntax errors, put something like this at the top of your
script:
use 5.010; # so filetest ops can stack
PORTING CAVEATS
With the arrival of RakuAST, it has become impossible to access the topic variable ($_) of the caller's scope. So Perl's idiom of calling -r or -w or any of the other -X builtins without arguments has become impossible
AUTHOR
Elizabeth Mattijsen liz@raku.rocks
Source can be located at: https://github.com/lizmat/P5-X . Comments and Pull Requests are welcome.
If you like this module, or what I’m doing more generally, committing to a small sponsorship would mean a great deal to me!
COPYRIGHT AND LICENSE
Copyright 2018, 2019, 2020, 2021, 2023, 2026 Elizabeth Mattijsen
Re-imagined from Perl as part of the CPAN Butterfly Plan.
This library is free software; you can redistribute it and/or modify it under the Artistic License 2.0.