DRAFT: Synopsis 16: IO / Name Services
Largely, the authors of the related Perl 5 docs. Larry Wall <larry@wall.org> Mark Stosberg <mark@summersault.com> Tim Nelson <wayland@wayland.id.au> Daniel Ruoso <daniel@ruoso.com>
Created: 12 Sep 2006 Last Modified: 19 Nov 2009 Version: 23
This is a draft document. Many of these functions will work as in Perl 5, except we're trying to rationalize everything into roles. For now you can assume most of the important functions will automatically be in the * namespace. However, with IO operations in particular, many of them are really methods on an IO handle, and if there is a corresponding global function, it's merely an exported version of the method.
In Perl 6, there are the standard IO handles, and any number of overriding inner filehandles for the same symbol.
The standard handles are our old familiar friends (with new names). Standard input changed from STDIN to $*IN, standard output changed from STDOUT to $*OUT, and standard error changed from STDERR to $*ERR. In Perl 6 these symbols represent more of a concept than a given filehandle, since the meaning is contextually determined. The process's version of these handles live in the PROCESS:: namespace, which is more global than the per-interpreter GLOBAL:: namespace.
$*IN
$*OUT
$*ERR
PROCESS::
GLOBAL::
When no explicit filehandle is used, the standard IO operators are defined in terms of the dynamic variables. So the print function prints to $*OUT, while warn warns to $*ERR. The lines() term inputs from $*ARGFILES which defaults to $*IN in the absence of any filenames. So any given dynamic scope (interpreter, thread, function or method call) may redefine the current meaning of any of those filehandles within the dynamic scope of itself and of its called routines.
print
warn
lines()
$*ARGFILES
So to put it another way, when you write something like
say "Howdy, world!"
the say function looks for the current meaning of $*OUT, and takes the closest definition it can find in its callers. If none of the callers have overridden the definition, it looks in the interpreter's GLOBAL namespace. If the interpreter hasn't overridden the meaning, it takes the meaning from PROCESS. In essence, any dynamic scope in Perl 6 is allowed to do IO redirection much like a Unix shell does with its subprocesses, albeit with a different syntax:
say
GLOBAL
PROCESS
{ temp $*OUT = open $newfile, :w; foo() # all stdout goes to $newfile } # stdout reverts to outer scope's definition
The roles and classes that define most of the functionality for IO are defined in S32-setting-library/IO.pod. The main functions used are listed in S29 with references to S32-setting-library/IO.pod.
The use of filenames requires a special quoting syntax. It works as follows:
qp{/path/to/file} q:p{/path/to/file}
Both of the above result in the same thing.
The quote characters can be any of the usual ones, although / is probably a bad choice for filenames.
The code shown above returns a Path object (or a descendant thereof).
Naturally you can also ask for interpolation in filenames:
qp:qq{$directory/$file} qq:p{$directory/$file}
There are a number of special adverbs that can be applied to the file quoting operator. Most of these are filesystem-specific. They confine what can be included in a filename.
Any path that starts with a "/" is considered an absolute path, otherwise the path is considered relative.
When creating a path with qp{}, the Path.Encoding attribute is set to $?ENC, unless the :bin modifier (see below) is used.
The default constraints can be set with the "use path" pragma, for example:
use path :posix; use path :modern; use path :local;
The default when in strict mode is "use path :posix", whereas the default in lax mode is "use path :local".
The :modern set of constraints paths are portable POSIX paths (see POSIX.1-2008 sections 4.7 and 3.276). If platform/filesystem specific behavior is needed, specific constraints should be applied as needed (see below).
The default constraints are to only allow "/" as separator and only allows portable POSIX filenames. That means A-Z, a-z, 0-9, <period>, <underscore>, and <hyphen>. Additionally, hyphen may not be the first character in the path.
In addition to the POSIX constraints above, the path should fit into 8 characters, followed by a full stop, and then three more characters. Only the one full stop should appear in the filename. Additionally, no path may be longer than 64 characters.
This is :win on a Windows platform, :unix on a Unix platform, etc. Note that this is specifically not portable between platforms with different constraint sets.
The :modern set of constraints are the same as :posix, except that they may contain any UTF-8 character, rather than just those listed.
We allow Windows style paths so converting and maintaining code on this platform is not a pain.
my Path $path = p:win{C:\Program Files\MS Access\file.file};
Note that this specifically excludes the backslash quoting usually used with q{}.
For Unix specific behavior we have a p:unix{} literal. Here the only limits are what is defined by the locale and the filesystem type. So we won't be able to write full Unicode if locale is set to Latin1.
my Path $path = p:unix{/usr/src/bla/myfile?:%.file};
If the above are causing problems, p:bin{} can be used as no checking is done here. However, this leaves the Path.Encoding attribute undefined, which means that certain features of Path will remain unavailable unless this attribute is set.
It is expected that other sets of constraints, such as VMS, DOS, and old-style Mac will be provided by modules.
The global variable $*CWD is a Path object with certain special properties, mainly:
* It must check whether the path exists before changing its value * It can only be assigned an absolute path; if you want to make relative changes, use the Array interface
$*CWD is specific to the current thread, unlike %*ENV<PATH> or the native getcwd/chdir path, which are both usually process-wide.
%*ENV<PATH>
The variable is used in at least these cases:
* When a Path object is created, if the string it is given is not an absolute path, then $*CWD is prepended to it. * When a subprocess is executed, it is executed with the current thread's $*CWD as its working directory.
role User { has $username; # Username (some descendants(?) may want to implement a real $name) has $id; # User ID has $dir; # Home directory for files }
method User new($Username?, $UID?) {...}
Creates a new User object, fetching the information either by username or user ID.
method write() {...}
Tries to write the current User object to the user database. This may well fail.
When converted to a Str, returns $username.
When converted to a Num, returns $uid.
role OS::Unix::User does User { has $password; has $gid; has $gecos; has $shell; }
All the information is naturally fetched from the system via getpwuid, getpwnam, or the like.
role Group { has $name; has $id; has @members; }
method Group new(:$Name, :$ID);
method write();
Tries to write the group entry into the system group database.
The NameServices role has a bunch of functions that between them will return the whole Name Services database between them, as lists of objects. The lists are specifically intended to be lazy.
role NameServices { method List of User users() {...} # getpwent, setpwent, endpwent method List of Group groups() {...} # getgrent, setgrent, endgrent method List of Service services() {...} # getservent, setservent, endservent method List of Protocol protocols() {...} # getprotoent, setprotoent, endprotoent method List of Network networks() {...} # getnetent, setnetent, endnetent method List of Host hosts() {...} # gethostent, sethostent, endhostent }
Please post errors and feedback to perl6-language. If you are making a general laundry list, please separate messages by topic.
To install Perl6::Doc, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Perl6::Doc
CPAN shell
perl -MCPAN -e shell install Perl6::Doc
For more information on module installation, please visit the detailed CPAN module installation guide.