golden hour

/usr/share/perl5/pod

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perl.pod	16.28 KB
perl5004delta.pod	54.92 KB
perl5005delta.pod	33.48 KB
perl5100delta.pod	54.23 KB
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perl5120delta.pod	87.18 KB
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perl58delta.pod	112.47 KB
perlaix.pod	19.96 KB
perlamiga.pod	5.61 KB
perlandroid.pod	8.03 KB
perlapi.pod	481.55 KB
perlapio.pod	20.84 KB
perlartistic.pod	6.85 KB
perlbook.pod	8.19 KB
perlboot.pod	294 B
perlbot.pod	304 B
perlbs2000.pod	7.81 KB
perlcall.pod	55.41 KB
perlcheat.pod	4.38 KB
perlclib.pod	9.38 KB
perlcn.pod	4.65 KB
perlcommunity.pod	6.82 KB
perlcygwin.pod	26.56 KB
perldata.pod	48.62 KB
perldbmfilter.pod	4.86 KB
perldebguts.pod	41.34 KB
perldebtut.pod	21.63 KB
perldebug.pod	38.46 KB
perldelta.pod	6.84 KB
perldeprecation.pod	20.34 KB
perldiag.pod	290.03 KB
perldos.pod	10.28 KB
perldsc.pod	25.01 KB
perldtrace.pod	7.77 KB
perlebcdic.pod	82.37 KB
perlembed.pod	36.69 KB
perlexperiment.pod	7.06 KB
perlfork.pod	13.04 KB
perlform.pod	16.22 KB
perlfreebsd.pod	1.58 KB
perlfunc.pod	394.31 KB
perlgit.pod	28.9 KB
perlgov.pod	14.14 KB
perlgpl.pod	13.49 KB
perlguts.pod	158.3 KB
perlhack.pod	42.15 KB
perlhacktips.pod	56.34 KB
perlhacktut.pod	6.01 KB
perlhaiku.pod	1.47 KB
perlhist.pod	54.85 KB
perlhpux.pod	29.89 KB
perlhurd.pod	1.95 KB
perlintern.pod	81.61 KB
perlinterp.pod	32.92 KB
perlintro.pod	21.62 KB
perliol.pod	33.99 KB
perlipc.pod	69.85 KB
perlirix.pod	4.31 KB
perljp.pod	8.23 KB
perlko.pod	11.92 KB
perllexwarn.pod	355 B
perllinux.pod	1.96 KB
perllocale.pod	72.38 KB
perllol.pod	9.36 KB
perlmacos.pod	998 B
perlmacosx.pod	11.84 KB
perlmod.pod	25.58 KB
perlmodinstall.pod	10.02 KB
perlmodlib.pod	74.56 KB
perlmodstyle.pod	22.06 KB
perlmroapi.pod	3.2 KB
perlnetware.pod	6.49 KB
perlnewmod.pod	10.78 KB
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perlobj.pod	34.88 KB
perlootut.pod	26.13 KB
perlop.pod	145.4 KB
perlopenbsd.pod	1.2 KB
perlopentut.pod	14.87 KB
perlos2.pod	91.16 KB
perlos390.pod	16.14 KB
perlos400.pod	4.65 KB
perlpacktut.pod	50.17 KB
perlperf.pod	48.71 KB
perlplan9.pod	5 KB
perlpod.pod	22.54 KB
perlpodspec.pod	67.02 KB
perlpolicy.pod	25.94 KB
perlport.pod	86.61 KB
perlpragma.pod	5.05 KB
perlqnx.pod	6.52 KB
perlre.pod	127.75 KB
perlreapi.pod	29.54 KB
perlrebackslash.pod	31.53 KB
perlrecharclass.pod	48.54 KB
perlref.pod	34.6 KB
perlreftut.pod	18.38 KB
perlreguts.pod	38.38 KB
perlrepository.pod	509 B
perlrequick.pod	18.69 KB
perlreref.pod	15.22 KB
perlretut.pod	119.66 KB
perlriscos.pod	1.49 KB
perlrun.pod	54.67 KB
perlsec.pod	26.95 KB
perlsecpolicy.pod	18.99 KB
perlsolaris.pod	29.14 KB
perlsource.pod	6.96 KB
perlstyle.pod	8.53 KB
perlsub.pod	72.66 KB
perlsymbian.pod	14.98 KB
perlsyn.pod	44.08 KB
perlsynology.pod	7.77 KB
perlthrtut.pod	45.43 KB
perltie.pod	38.39 KB
perltoc.pod	685.35 KB
perltodo.pod	372 B
perltooc.pod	294 B
perltoot.pod	294 B
perltrap.pod	10.37 KB
perltru64.pod	8.29 KB
perltw.pod	4.36 KB
perlunicode.pod	89.21 KB
perlunicook.pod	25.06 KB
perlunifaq.pod	13.32 KB
perluniintro.pod	37.74 KB
perluniprops.pod	431.26 KB
perlunitut.pod	7.76 KB
perlutil.pod	7.12 KB
perlvar.pod	80.64 KB
perlvms.pod	49.63 KB
perlvos.pod	3.75 KB
perlwin32.pod	39.37 KB

Edit: perlhacktut.pod

=encoding utf8

=for comment
Consistent formatting of this file is achieved with:
  perl ./Porting/podtidy pod/perlhacktut.pod

=head1 NAME

perlhacktut - Walk through the creation of a simple C code patch

=head1 DESCRIPTION

This document takes you through a simple patch example.

If you haven't read L<perlhack> yet, go do that first! You might also
want to read through L<perlsource> too.

Once you're done here, check out L<perlhacktips> next.

=head1 EXAMPLE OF A SIMPLE PATCH

Let's take a simple patch from start to finish.

Here's something Larry suggested: if a C is the first active format
during a C<pack>, (for example, C<pack "U3C8", @stuff>) then the
resulting string should be treated as UTF-8 encoded.

If you are working with a git clone of the Perl repository, you will
want to create a branch for your changes. This will make creating a
proper patch much simpler. See the L<perlgit> for details on how to do
this.

=head2 Writing the patch

How do we prepare to fix this up? First we locate the code in question
- the C<pack> happens at runtime, so it's going to be in one of the
F<pp> files. Sure enough, C<pp_pack> is in F<pp.c>. Since we're going
to be altering this file, let's copy it to F<pp.c~>.

[Well, it was in F<pp.c> when this tutorial was written. It has now
been split off with C<pp_unpack> to its own file, F<pp_pack.c>]

Now let's look over C<pp_pack>: we take a pattern into C<pat>, and then
loop over the pattern, taking each format character in turn into
C<datum_type>. Then for each possible format character, we swallow up
the other arguments in the pattern (a field width, an asterisk, and so
on) and convert the next chunk input into the specified format, adding
it onto the output SV C<cat>.

How do we know if the C is the first format in the C<pat>? Well, if
we have a pointer to the start of C<pat> then, if we see a C we can
test whether we're still at the start of the string. So, here's where
C<pat> is set up:

STRLEN fromlen;
    char *pat = SvPVx(*++MARK, fromlen);
    char *patend = pat + fromlen;
    I32 len;
    I32 datumtype;
    SV *fromstr;

We'll have another string pointer in there:

STRLEN fromlen;
    char *pat = SvPVx(*++MARK, fromlen);
    char *patend = pat + fromlen;
 +  char *patcopy;
    I32 len;
    I32 datumtype;
    SV *fromstr;

And just before we start the loop, we'll set C<patcopy> to be the start
of C<pat>:

items = SP - MARK;
 MARK++;
 SvPVCLEAR(cat);
 + patcopy = pat;
 while (pat < patend) {

Now if we see a C which was at the start of the string, we turn on
the C<UTF8> flag for the output SV, C<cat>:

+ if (datumtype == 'U' && pat==patcopy+1)
 + SvUTF8_on(cat);
 if (datumtype == '#') {
 while (pat < patend && *pat != '\n')
 pat++;

Remember that it has to be C<patcopy+1> because the first character of
the string is the C which has been swallowed into C<datumtype!>

Oops, we forgot one thing: what if there are spaces at the start of the
pattern? C<pack(" U*", @stuff)> will have C as the first active
character, even though it's not the first thing in the pattern. In this
case, we have to advance C<patcopy> along with C<pat> when we see
spaces:

if (isSPACE(datumtype))
        continue;

needs to become

if (isSPACE(datumtype)) {
        patcopy++;
        continue;
    }

OK. That's the C part done. Now we must do two additional things before
this patch is ready to go: we've changed the behaviour of Perl, and so
we must document that change. We must also provide some more regression
tests to make sure our patch works and doesn't create a bug somewhere
else along the line.

=head2 Testing the patch

The regression tests for each operator live in F<t/op/>, and so we make
a copy of F<t/op/pack.t> to F<t/op/pack.t~>. Now we can add our tests
to the end. First, we'll test that the C does indeed create Unicode
strings.

t/op/pack.t has a sensible ok() function, but if it didn't we could use
the one from t/test.pl.

require './test.pl';
 plan( tests => 159 );

so instead of this:

print 'not ' unless "1.20.300.4000" eq sprintf "%vd",
                                               pack("U*",1,20,300,4000);
 print "ok $test\n"; $test++;

we can write the more sensible (see L<Test::More> for a full
explanation of is() and other testing functions).

is( "1.20.300.4000", sprintf "%vd", pack("U*",1,20,300,4000),
                                       "U* produces Unicode" );

Now we'll test that we got that space-at-the-beginning business right:

is( "1.20.300.4000", sprintf "%vd", pack("  U*",1,20,300,4000),
                                     "  with spaces at the beginning" );

And finally we'll test that we don't make Unicode strings if C is
B<not> the first active format:

isnt( v1.20.300.4000, sprintf "%vd", pack("C0U*",1,20,300,4000),
                                       "U* not first isn't Unicode" );

Mustn't forget to change the number of tests which appears at the top,
or else the automated tester will get confused. This will either look
like this:

print "1..156\n";

or this:

plan( tests => 156 );

We now compile up Perl, and run it through the test suite. Our new
tests pass, hooray!

=head2 Documenting the patch

Finally, the documentation. The job is never done until the paperwork
is over, so let's describe the change we've just made. The relevant
place is F<pod/perlfunc.pod>; again, we make a copy, and then we'll
insert this text in the description of C<pack>:

=item *

If the pattern begins with a C, the resulting string will be treated
 as UTF-8-encoded Unicode. You can force UTF-8 encoding on in a string
 with an initial C<U0>, and the bytes that follow will be interpreted as
 Unicode characters. If you don't want this to happen, you can begin
 your pattern with C<C0> (or anything else) to force Perl not to UTF-8
 encode your string, and then follow this with a C<U*> somewhere in your
 pattern.

=head2 Submit

See L<perlhack> for details on how to submit this patch.

=head1 AUTHOR

This document was originally written by Nathan Torkington, and is
maintained by the perl5-porters mailing list.