10.8. Line-Based Input
Prefer line-based I/O to slurping .
Reading in an entire file in a single <> operation is colloquially known as "slurping". But the considerations of memory allocation discussed in the previous section mean that slurping the contents of a file and then manipulating those contents monolithically, like so:
# Slurp the entire file (see the next guideline)...
my $text = do { local $/; <> };
# Wash its mouth out...
$text =~ s/$EXPLETIVE/[DELETED]/gxms;
# Print it all back out...
print $text;
is generally slower, less robust, and less scalable than processing the contents a line at a time:
while (my $line = <>) {
$line =~ s/$expletive/[DELETED]/gxms;
print $line;
}
Reading an entire file into memory makes sense only when the file is unstable in some way, or is being updated asynchronously and you need a "snapshot", or if your planned text processing is likely to cross line boundaries:
sub get_C_code {
my ($filename) = @_;
# Get a handle on the code...
open my $in, '<', $filename
or croak "Can't open C file '$filename': $OS_ERROR";
# Read it all in...
my $code = do { local $/; <$in> };
# Convert any C-style comment to a single space...
use Regexp::Common; # See Chapter 12
$code =~ s{ $RE{comment}{C} }{$SPACE}gxms;
return $code;
}
Because C comments can span multiple lines, it's necessary to load the entire file into memory at once so the pattern can detect such cases.
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