(contributed by brian d foy)
-If you want to C<write> into a string, you just have to <open> a
+If you want to C<write> into a string, you just have to <open> a
filehandle to a string, which Perl has been able to do since Perl 5.6:
open FH, '>', \my $string;
write( FH );
-
+
Since you want to be a good programmer, you probably want to use a lexical
filehandle, even though formats are designed to work with bareword filehandles
-since the default format names take the filehandle name. However, you can
+since the default format names take the filehandle name. However, you can
control this with some Perl special per-filehandle variables: C<$^>, which
names the top-of-page format, and C<$~> which shows the line format. You have
to change the default filehandle to set these variables:
open my($fh), '>', \my $string;
-
+
{ # set per-filehandle variables
my $old_fh = select( $fh );
$~ = 'ANIMAL';
format ANIMAL_TOP =
ID Type Name
.
-
+
format ANIMAL =
@## @<<< @<<<<<<<<<<<<<<
$id, $type, $name
.
Although write can work with lexical or package variables, whatever variables
-you use have to scope in the format. That most likely means you'll want to
+you use have to scope in the format. That most likely means you'll want to
localize some package variables:
{
local( $id, $type, $name ) = qw( 12 cat Buster );
write( $fh );
}
-
+
print $string;
-There are also some tricks that you can play with C<formline> and the
+There are also some tricks that you can play with C<formline> and the
accumulator variable C<$^A>, but you lose a lot of the value of formats
since C<formline> won't handle paging and so on. You end up reimplementing
formats when you use them.
map_file my $string, $filename;
Once mapped, you can treat C<$string> as you would any other string.
-Since you don't actually load the data, mmap-ing is very fast and does
-not increase your memory footprint.
+Since you don't necessarily have to load the data, mmap-ing can be
+very fast and may not increase your memory footprint.
-If you really want to load the entire file, you can use the
-C<File::Slurp> module to do it in one step.
+If you want to load the entire file, you can use the C<File::Slurp>
+module to do it in one one simple and efficient step:
use File::Slurp;
You should think long and hard about why you need everything loaded at
once. It's just not a scalable solution. You might also find it more
-fun to use the standard Tie::File module, or the DB_File module's
-$DB_RECNO bindings, which allow you to tie an array to a file so that
+fun to use the standard C<Tie::File> module, or the C<DB_File> module's
+C<$DB_RECNO> bindings, which allow you to tie an array to a file so that
accessing an element the array actually accesses the corresponding
line in the file.
You can read the entire filehandle contents into a scalar.
+ my $var;
{
local $/;
open my $fh, '<', $file or die "can't open $file: $!";
That temporarily undefs your record separator, and will automatically
close the file at block exit. If the file is already open, just use this:
- $var = do { local $/; <$fh> };
+ my $var = do { local $/; <$fh> };
+
+You can do that one better by using a localized C<@ARGV> so you can
+eliminate the C<open>:
+
+ my $var = do { local( @ARGV, $/ ) = $file; <> };
-For ordinary files you can also use the read function.
+For ordinary files you can also use the C<read> function.
read( $fh, $var, -s $fh );
-The third argument tests the byte size of the data on the INPUT filehandle
-and reads that many bytes into the buffer $var.
+That third argument tests the byte size of the data on the C<INPUT> filehandle
+and reads that many bytes into the buffer C<$var>.
=head2 How can I read in a file by paragraphs?
X<file, reading by paragraphs>
https://perl5.git.perl.org / perl5.git / blobdiff