The new format type 'Z' is useful for packing and unpacking null-terminated
strings. See L<perlfunc/"pack">.
+=head1 Significant bug fixes
+
+=head2 E<lt>HANDLEE<gt> on empty files
+
+With C<$/> set to C<undef>, slurping an empty file returns a string of
+zero length (instead of C<undef>, as it used to) for the first time the
+HANDLE is read. Subsequent reads yield C<undef>.
+
+This means that the following will append "foo" to an empty file (it used
+to not do anything before):
+
+ perl -0777 -pi -e 's/^/foo/' empty_file
+
+Note that the behavior of:
+
+ perl -pi -e 's/^/foo/' empty_file
+
+is unchanged (it continues to leave the file empty).
+
=head1 Supported Platforms
=over 4
=head1 Utility Changes
+=head2 New Modules
+
+=over
+
Todo.
+=back
+
+=head2 Changes in existing modules
+
+=over
+
+=item Exporter
+
+Exporter::expand() takes an import list and returns the expanded
+list of names.
+
+=back
+
=head1 Documentation Changes
=over 4
=item readline EXPR
-Reads from the filehandle whose typeglob is contained in EXPR. In scalar context, a single line
-is read and returned. In list context, reads until end-of-file is
-reached and returns a list of lines (however you've defined lines
-with C<$/> or C<$INPUT_RECORD_SEPARATOR>).
+Reads from the filehandle whose typeglob is contained in EXPR. In scalar
+context, each call reads and returns the next line, until end-of-file is
+reached, whereupon the subsequent call returns undef. In list context,
+reads until end-of-file is reached and returns a list of lines. Note that
+the notion of "line" used here is however you may have defined it
+with C<$/> or C<$INPUT_RECORD_SEPARATOR>). See L<perlvar/"$/">.
+
+When C<$/> is set to C<undef> and when readline() is in a scalar
+context (i.e. file slurp mode), it returns C<''> the first time,
+followed by C<undef> subsequently.
+
This is the internal function implementing the C<E<lt>EXPRE<gt>>
operator, but you can use it directly. The C<E<lt>EXPRE<gt>>
operator is discussed in more detail in L<perlop/"I/O Operators">.
=head2 I/O Operators
There are several I/O operators you should know about.
+
A string enclosed by backticks (grave accents) first undergoes
variable substitution just like a double quoted string. It is then
interpreted as a command, and the output of that command is the value
always undergo shell expansion as well, see L<perlsec> for
security concerns.)
-Evaluating a filehandle in angle brackets yields the next line from
-that file (newline, if any, included), or C<undef> at end of file.
-Ordinarily you must assign that value to a variable, but there is one
+In a scalar context, evaluating a filehandle in angle brackets yields the
+next line from that file (newline, if any, included), or C<undef> at
+end-of-file. When C<$/> is set to C<undef> (i.e. file slurp mode),
+it returns C<''> the first time, followed by C<undef> subsequently.
+
+Ordinarily you must assign the returned value to a variable, but there is one
situation where an automatic assignment happens. I<If and ONLY if> the
input symbol is the only thing inside the conditional of a C<while> or
C<for(;;)> loop, the value is automatically assigned to the variable
filehandles C<stdin>, C<stdout>, and C<stderr> will also work except in
packages, where they would be interpreted as local identifiers rather
than global.) Additional filehandles may be created with the open()
-function. See L<perlfunc/open()> for details on this.
+function. See L<perlfunc/open> for details on this.
If a E<lt>FILEHANDLEE<gt> is used in a context that is looking for a list, a
list consisting of all the input lines is returned, one line per list
element. It's easy to make a I<LARGE> data space this way, so use with
care.
+E<lt>FILEHANDLEE<gt> may also be spelt readline(FILEHANDLE). See
+L<perlfunc/readline>.
+
The null filehandle E<lt>E<gt> is special and can be used to emulate the
behavior of B<sed> and B<awk>. Input from E<lt>E<gt> comes either from
standard input, or from each file listed on the command line. Here's
character belongs to the next paragraph, even if it's a newline.
(Mnemonic: / is used to delimit line boundaries when quoting poetry.)
- undef $/;
- $_ = <FH>; # whole file now here
+ undef $/; # enable "slurp" mode
+ $_ = <FH>; # whole file now here
s/\n[ \t]+/ /g;
Remember: the value of $/ is a string, not a regexp. AWK has to be
sv = sv_2mortal(NEWSV(57, 80));
offset = 0;
}
+
+/* flip-flop EOF state for a snarfed empty file */
+#define SNARF_EOF(gimme,rs,io,sv) \
+ ((gimme != G_SCALAR || SvCUR(sv) \
+ || (IoFLAGS(io) & IOf_NOLINE) || IoLINES(io) || !RsSNARF(rs)) \
+ ? ((IoFLAGS(io) &= ~IOf_NOLINE), TRUE) \
+ : ((IoFLAGS(io) |= IOf_NOLINE), FALSE))
+
for (;;) {
- if (!sv_gets(sv, fp, offset)) {
+ if (!sv_gets(sv, fp, offset)
+ && (type == OP_GLOB || SNARF_EOF(gimme, PL_rs, io, sv)))
+ {
PerlIO_clearerr(fp);
if (IoFLAGS(io) & IOf_ARGV) {
fp = nextargv(PL_last_in_gv);
#define IOf_FLUSH 4 /* this fp wants a flush after write op */
#define IOf_DIDTOP 8 /* just did top of form */
#define IOf_UNTAINT 16 /* consider this fp (and its data) "safe" */
+#define IOf_NOLINE 32 /* slurped a pseudo-line from empty file */
/* The following macros define implementation-independent predicates on SVs. */
#!./perl
-# $RCSfile: argv.t,v $$Revision: 4.1 $$Date: 92/08/07 18:27:25 $
+print "1..6\n";
-print "1..5\n";
-
-open(try, '>Io.argv.tmp') || (die "Can't open temp file.");
+open(try, '>Io.argv.tmp') || (die "Can't open temp file: $!");
print try "a line\n";
close try;
else
{print "not ok 5\n";}
-unlink 'Io.argv.tmp';
+open(try, '>Io.argv.tmp') or die "Can't open temp file: $!";
+close try;
+@ARGV = 'Io.argv.tmp';
+$^I = '';
+$/ = undef;
+while (<>) {
+ s/^/ok 6\n/;
+ print;
+}
+open(try, '<Io.argv.tmp') or die "Can't open temp file: $!";
+print while <try>;
+close try;
+
+END { unlink 'Io.argv.tmp' }
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