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approximated by the names of the elements of the C<fldata_t> struct (see the 
documentaton for the C<fldata()> C RTL routine for further information).

For example:

    use OS390::Stdio qw(get_dcb);
    my %slate_dcb = get_dcb("//SEDIMENT.SLATE");
    for (sort(keys(%slate_dcb))) {
        print "$_ = $slate_dcb{$_}\n";
    }

For an example using the older data set handle mechanism:

    use OS390::Stdio qw(mvsopen get_dcb);
    my $dshandle = mvsopen("//SEDIMENT.SLATE","r");
    my %slate_dcb = get_dcb($dshandle);
    close($dshandle);
    for (sort(keys(%slate_dcb))) {
        print "$_ = $slate_dcb{$_}\n";
    }

For the inverse (i.e. setting data set attributes) use appropriate 
arguments with either C<mvsopen>, C<dynalloc>, or C<svc99>.  For just 
the filename you can use C<getname> in place of C<get_dcb>.

=item getname NAME

=item getname DSH

The C<getname> function returns the full data set filename associated
either with the given name or with a supplied Perl I/O handle 
(via C<fldata()>).  If an error occurs, it returns C<undef>.

As an example consider:

    $fullname = getname("//FOO.BAR");
    $hlq = $fullname;
    $hlq =~ s/\'([^\.]+)\..*/$1/;  # strip leading ' and trailing DS names
    print "The high level qualifier (HLQ) is $hlq\n";

The version of that previous example carried out with a Data Set Handle
might appear as:

    $dshandle = mvsopen("//FOO.BAR","r");
    $fullname = getname($dshandle);
    $hlq = $fullname;
    $hlq =~ s/\'([^\.]+)\..*/$1/;  # strip leading ' and trailing DS names
    print "The high level qualifier (HLQ) is $hlq\n";

or, assuming you are authorized to do so, in order to switch 
to a different HLQ:

    $mydshandle = mvsopen("//FOO.BAR","r");
    $myfullname = getname($mydshandle);
    $bobsuid = '214';
    setuid($bobsuid);
    $bobsdshandle = mvsopen("//FOO.BAR","r");
    $bobsfullname = getname($bobsdshandle);
    $bobshlq = $bobsfullname;
    $bobshlq =~ s/\'([^\.]+)\..*/$1/;
    print "Bob's pwname is ",(getpwuid($<))[0],"\n";
    print "Bob's high level qualifier (HLQ) is $bobshlq\n";

Note that both of these examples assume that UIDs map directly to 
profile prefixes, whereas they may not in general.  To obtain more
extensive information for a given data set handle see C<get_dcb>.

=item mvsopen NAME MODE

The C<mvsopen> function enables you to specify optional arguments
to the CRTL when opening a data set.  Its operation is similar to the 
built-in Perl C<open> function (see L<perlfunc> for a complete description),
but it will only open normal data sets; it cannot open pipes or duplicate
existing I/O handles.  The C<MODE> is typically taken from:

    qw(r w a r+ w+ a+ rb wb ab rt wt at rb+ wb+ ab+ rt+ wt+ at+)

Additional C<MODE> keyword parameters can be passed from:

    qw(acc= blksize= byteseek lrecl= recfm= type= asis password= noseek)

(See the B<C/C++ MVS Programming Guide> and the 
B<C/C++ Run-Time Library Reference> descriptions of C<fopen()> for detailed 
information on C<NAME> and C<MODE> arguments.)  If successful, C<mvsopen> 
returns a data set handle; if an error occurs, it returns C<undef>.

You can use the data set handle returned by C<mvsopen> just as you
would any other Perl file handle.  The class OS390::Stdio ISA
IO::File, so you can call IO::File methods using the handle
returned by C<mvsopen>.  However, C<use>ing OS390::Stdio does not
automatically C<use> IO::File; you must do so explicitly in
your program if you want to call IO::File methods.  This is
done to avoid the overhead of initializing the IO::File package
in programs which intend to use the handle returned by C<mvsopen>
as a normal Perl data set handle only.  When the scalar containing
a OS390::Stdio data set handle is overwritten, C<undef>d, or goes
out of scope, the associated data set is closed automatically.

=item mvswrite DSH EXPR LEN

The C<mvswrite> function provides access to stdio's C<fwrite()> function.
For example:

    use OS390::Stdio qw(mvsopen mvswrite);
    my $dshandle = mvsopen("//BED.ROCK","w+");
    my $fred,$data,$chrs_written;
    $fred = 100.00;
    $data = sprintf("Fred's salary is \$%3.2f",$fred);
    $chrs_written = mvswrite($dshandle,$data,length($data));
    close($dshandle);

=item pds_mem NAME

=item pds_mem NAME, FLAG

Returns a list of members for the named PDS directory.  Alias names 
may be returned depending on the value of the optional 
FLAG argument:

    FLAG   pds_mem() returns
           member names (if any) - this is the default