Section 10.8. Line-Based Input

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.