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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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