FAQ 6.4 I put a regular expression into $/ but it didn't work. What's wrong?



This is an excerpt from the latest version perlfaq6.pod, which
comes with the standard Perl distribution. These postings aim to
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to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

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6.4: I put a regular expression into $/ but it didn't work. What's wrong?

Up to Perl 5.8.0, $/ has to be a string. This may change in 5.10, but
don't get your hopes up. Until then, you can use these examples if you
really need to do this.

If you have File::Stream, this is easy.

use File::Stream;

my $stream = File::Stream->new(
$filehandle,
separator => qr/\s*,\s*/,
);

print "$_\n" while <$stream>;

If you don't have File::Stream, you have to do a little more work.

You can use the four argument form of sysread to continually add to a
buffer. After you add to the buffer, you check if you have a complete
line (using your regular expression).

local $_ = "";
while( sysread FH, $_, 8192, length ) {
while( s/^((?s).*?)your_pattern/ ) {
my $record = $1;
# do stuff here.
}
}

You can do the same thing with foreach and a match using the
c flag and the \G anchor, if you do not mind your entire file
being in memory at the end.

local $_ = "";
while( sysread FH, $_, 8192, length ) {
foreach my $record ( m/\G((?s).*?)your_pattern/gc ) {
# do stuff here.
}
substr( $_, 0, pos ) = "" if pos;
}



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