plain paranoid, you can force the correct interpretation with curly
braces as above.
-A line-oriented form of quoting is based on the shell "here-document"
-syntax. Following a C<< << >> you specify a string to terminate
-the quoted material, and all lines following the current line down to
-the terminating string are the value of the item. The terminating
-string may be either an identifier (a word), or some quoted text. If
-quoted, the type of quotes you use determines the treatment of the
-text, just as in regular quoting. An unquoted identifier works like
-double quotes. There must be no space between the C<< << >> and
-the identifier, unless the identifier is quoted. (If you put a space it
-will be treated as a null identifier, which is valid, and matches the first
-empty line.) The terminating string must appear by itself (unquoted and
-with no surrounding whitespace) on the terminating line.
-
- print <<EOF;
- The price is $Price.
- EOF
-
- print << "EOF"; # same as above
- The price is $Price.
- EOF
-
- print << `EOC`; # execute commands
- echo hi there
- echo lo there
- EOC
-
- print <<"foo", <<"bar"; # you can stack them
- I said foo.
- foo
- I said bar.
- bar
-
- myfunc(<< "THIS", 23, <<'THAT');
- Here's a line
- or two.
- THIS
- and here's another.
- THAT
-
-Just don't forget that you have to put a semicolon on the end
-to finish the statement, as Perl doesn't know you're not going to
-try to do this:
-
- print <<ABC
- 179231
- ABC
- + 20;
-
-If you want your here-docs to be indented with the
-rest of the code, you'll need to remove leading whitespace
-from each line manually:
-
- ($quote = <<'FINIS') =~ s/^\s+//gm;
- The Road goes ever on and on,
- down from the door where it began.
- FINIS
-
-If you use a here-doc within a delimited construct, such as in C<s///eg>,
-the quoted material must come on the lines following the final delimiter.
-So instead of
-
- s/this/<<E . 'that'
- the other
- E
- . 'more '/eg;
-
-you have to write
-
- s/this/<<E . 'that'
- . 'more '/eg;
- the other
- E
-
-If the terminating identifier is on the last line of the program, you
-must be sure there is a newline after it; otherwise, Perl will give the
-warning B<Can't find string terminator "END" anywhere before EOF...>.
-
-Additionally, the quoting rules for the identifier are not related to
-Perl's quoting rules -- C<q()>, C<qq()>, and the like are not supported
-in place of C<''> and C<"">, and the only interpolation is for backslashing
-the quoting character:
-
- print << "abc\"def";
- testing...
- abc"def
-
-Finally, quoted strings cannot span multiple lines. The general rule is
-that the identifier must be a string literal. Stick with that, and you
-should be safe.
+If you're looking for the information on how to use here-documents,
+which used to be here, that's been moved to L<perlop> in the section on
+L<Quote and Quote-like Operators>.
=head2 List value constructors
length of the array; the following assigns the value 3 to $foo:
@foo = ('cc', '-E', $bar);
- $foo = @foo; # $foo gets 3
+ $foo = @foo; # $foo gets 3
You may have an optional comma before the closing parenthesis of a
list literal, so that you can say:
@foo = (
- 1,
- 2,
- 3,
+ 1,
+ 2,
+ 3,
);
To use a here-document to assign an array, one line per element,
you might use an approach like this:
@sauces = <<End_Lines =~ m/(\S.*\S)/g;
- normal tomato
- spicy tomato
- green chile
- pesto
- white wine
+ normal tomato
+ spicy tomato
+ green chile
+ pesto
+ white wine
End_Lines
LISTs do automatic interpolation of sublists. That is, when a LIST is
List assignment in scalar context returns the number of elements
produced by the expression on the right side of the assignment:
- $x = (($foo,$bar) = (3,2,1)); # set $x to 3, not 2
- $x = (($foo,$bar) = f()); # set $x to f()'s return count
+ $x = (($foo,$bar) = (3,2,1)); # set $x to 3, not 2
+ $x = (($foo,$bar) = f()); # set $x to f()'s return count
This is handy when you want to do a list assignment in a Boolean
context, because most list functions return a null list when finished,
This makes it nice for initializing hashes:
%map = (
- red => 0x00f,
- blue => 0x0f0,
- green => 0xf00,
+ red => 0x00f,
+ blue => 0x0f0,
+ green => 0xf00,
);
or for initializing hash references to be used as records:
$rec = {
- witch => 'Mable the Merciless',
- cat => 'Fluffy the Ferocious',
- date => '10/31/1776',
+ witch => 'Mable the Merciless',
+ cat => 'Fluffy the Ferocious',
+ date => '10/31/1776',
};
or for using call-by-named-parameter to complicated functions:
$field = $query->radio_group(
- name => 'group_name',
+ name => 'group_name',
values => ['eenie','meenie','minie'],
default => 'meenie',
linebreak => 'true',
A common way to access an array or a hash is one scalar element at a
time. You can also subscript a list to get a single element from it.
- $whoami = $ENV{"USER"}; # one element from the hash
- $parent = $ISA[0]; # one element from the array
- $dir = (getpwnam("daemon"))[7]; # likewise, but with list
+ $whoami = $ENV{"USER"}; # one element from the hash
+ $parent = $ISA[0]; # one element from the array
+ $dir = (getpwnam("daemon"))[7]; # likewise, but with list
A slice accesses several elements of a list, an array, or a hash
simultaneously using a list of subscripts. It's more convenient
than writing out the individual elements as a list of separate
scalar values.
- ($him, $her) = @folks[0,-1]; # array slice
- @them = @folks[0 .. 3]; # array slice
- ($who, $home) = @ENV{"USER", "HOME"}; # hash slice
- ($uid, $dir) = (getpwnam("daemon"))[2,7]; # list slice
+ ($him, $her) = @folks[0,-1]; # array slice
+ @them = @folks[0 .. 3]; # array slice
+ ($who, $home) = @ENV{"USER", "HOME"}; # hash slice
+ ($uid, $dir) = (getpwnam("daemon"))[2,7]; # list slice
Since you can assign to a list of variables, you can also assign to
an array or hash slice.
@days[3..5] = qw/Wed Thu Fri/;
@colors{'red','blue','green'}
- = (0xff0000, 0x0000ff, 0x00ff00);
+ = (0xff0000, 0x0000ff, 0x00ff00);
@folks[0, -1] = @folks[-1, 0];
The previous assignments are exactly equivalent to
($days[3], $days[4], $days[5]) = qw/Wed Thu Fri/;
($colors{'red'}, $colors{'blue'}, $colors{'green'})
- = (0xff0000, 0x0000ff, 0x00ff00);
+ = (0xff0000, 0x0000ff, 0x00ff00);
($folks[0], $folks[-1]) = ($folks[0], $folks[-1]);
Since changing a slice changes the original array or hash that it's
foreach (@array[ 4 .. 10 ]) { s/peter/paul/ }
foreach (@hash{keys %hash}) {
- s/^\s+//; # trim leading whitespace
- s/\s+$//; # trim trailing whitespace
- s/(\w+)/\u\L$1/g; # "titlecase" words
+ s/^\s+//; # trim leading whitespace
+ s/\s+$//; # trim trailing whitespace
+ s/(\w+)/\u\L$1/g; # "titlecase" words
}
A slice of an empty list is still an empty list. Thus:
is returned:
while ( ($home, $user) = (getpwent)[7,0]) {
- printf "%-8s %s\n", $user, $home;
+ printf "%-8s %s\n", $user, $home;
}
As noted earlier in this document, the scalar sense of list assignment
For example:
sub newopen {
- my $path = shift;
- local *FH; # not my!
- open (FH, $path) or return undef;
- return *FH;
+ my $path = shift;
+ local *FH; # not my!
+ open (FH, $path) or return undef;
+ return *FH;
}
$fh = newopen('/etc/passwd');
sub myopen {
open my $fh, "@_"
- or die "Can't open '@_': $!";
- return $fh;
+ or die "Can't open '@_': $!";
+ return $fh;
}
{
my $f = myopen("</etc/motd");
- print <$f>;
- # $f implicitly closed here
+ print <$f>;
+ # $f implicitly closed here
}
Another way to create anonymous filehandles is with the Symbol
qr{} Pattern yes*
s{}{} Substitution yes*
tr{}{} Transliteration no (but see below)
+ <<EOF here-doc yes*
* unless the delimiter is ''.
eval "tr/$oldlist/$newlist/, 1" or die $@;
+=item <<EOF
+
+A line-oriented form of quoting is based on the shell "here-document"
+syntax. Following a C<< << >> you specify a string to terminate
+the quoted material, and all lines following the current line down to
+the terminating string are the value of the item. The terminating
+string may be either an identifier (a word), or some quoted text. If
+quoted, the type of quotes you use determines the treatment of the
+text, just as in regular quoting. An unquoted identifier works like
+double quotes. There must be no space between the C<< << >> and
+the identifier, unless the identifier is quoted. (If you put a space it
+will be treated as a null identifier, which is valid, and matches the first
+empty line.) The terminating string must appear by itself (unquoted and
+with no surrounding whitespace) on the terminating line.
+
+ print <<EOF;
+ The price is $Price.
+ EOF
+
+ print << "EOF"; # same as above
+ The price is $Price.
+ EOF
+
+ print << `EOC`; # execute commands
+ echo hi there
+ echo lo there
+ EOC
+
+ print <<"foo", <<"bar"; # you can stack them
+ I said foo.
+ foo
+ I said bar.
+ bar
+
+ myfunc(<< "THIS", 23, <<'THAT');
+ Here's a line
+ or two.
+ THIS
+ and here's another.
+ THAT
+
+Just don't forget that you have to put a semicolon on the end
+to finish the statement, as Perl doesn't know you're not going to
+try to do this:
+
+ print <<ABC
+ 179231
+ ABC
+ + 20;
+
+If you want your here-docs to be indented with the
+rest of the code, you'll need to remove leading whitespace
+from each line manually:
+
+ ($quote = <<'FINIS') =~ s/^\s+//gm;
+ The Road goes ever on and on,
+ down from the door where it began.
+ FINIS
+
+If you use a here-doc within a delimited construct, such as in C<s///eg>,
+the quoted material must come on the lines following the final delimiter.
+So instead of
+
+ s/this/<<E . 'that'
+ the other
+ E
+ . 'more '/eg;
+
+you have to write
+
+ s/this/<<E . 'that'
+ . 'more '/eg;
+ the other
+ E
+
+If the terminating identifier is on the last line of the program, you
+must be sure there is a newline after it; otherwise, Perl will give the
+warning B<Can't find string terminator "END" anywhere before EOF...>.
+
+Additionally, the quoting rules for the identifier are not related to
+Perl's quoting rules -- C<q()>, C<qq()>, and the like are not supported
+in place of C<''> and C<"">, and the only interpolation is for backslashing
+the quoting character:
+
+ print << "abc\"def";
+ testing...
+ abc"def
+
+Finally, quoted strings cannot span multiple lines. The general rule is
+that the identifier must be a string literal. Stick with that, and you
+should be safe.
+
=back
=head2 Gory details of parsing quoted constructs
projects / p5sagit/p5-mst-13.2.git / commitdiff