June 19 2011: Reading files

Originally published on 19 June 2011 by Carl Mäsak.

Tomorrow we’ll be writing a game.

In order to do that, we’ll need to be able to read from files. We’ll learn two simple ways in this post.

my $contents = slurp("my_file");

This one reads the entire contents of a file and stores it in $contents. If it’s a big file, you’ll get a long string. Sometimes that is what you want.

Here’s one that can also come in handy:

my @lines = lines("my_file");

As you see, we’re now storing the contents of the file in an array; that’s because lines returns all the lines of the file as individual strings.

You could say that lines is a bit of a specialisation of slurp. We could as well have used slurp and a function called split:

my @lines = slurp("my_file").split("\n");

split does what you probably suspect it does: it takes a string and splits it into pieces. The pieces are determined by some delimiter (in this case "\n") that says where to split the string.

If split looks through a string for the things it wants to throw away, its cousin comb sifts through a string for the things it wants to keep:

say join " ", "abc123def456".split(/\d+/);    # "abc def"
say join " ", "abc123def456".comb(/\d+/);     # "123 456"

A very useful special case of comb is when you want all the individual characters of a string:

say join " ", "Hello World".`comb`;           # "H e l l o   W o r l d"

Hang around for tomorrow’s game. Because we’re reading from file, the actual game is nice and short.