From: PerlFAQ Server on
This is an excerpt from the latest version perlfaq6.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

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

$/ has to be a string. 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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