95. The cat utility

Create the equivalent of the UNIX cat utility that copies its STDIN input directly to STDOUT.

Reading from the input and sending it to the output is a relatively easy task. The $*IN handle is by default connected to STDIN. Being an object of the IO::Handle type, it has the slurp method that returns the whole input text in one go. What is left to do, is just to print it to the output, which defaults to STDOUT.

Here’s the complete program:

say $*IN.slurp;

🖥 This program reads the local environment (files, directories, or the command line), so it runs on your own computer but not in the sandboxed in-browser engine.

This works well, and we can use it via the command line:

$ raku cat.rk < file1.txt > file2.txt

However, in the interactive mode, the program does not replicate each entered line, but instead, it waits until the end of the output (say, until you press Ctrl+D). This behaviour is fully explainable because of the use of the slurp method.

Let us modify the program so that it prints each line as soon as it is entered. The IO::Handle class has another method, get, which reads one line from the handle and returns it. Create a loop and print the line after it is delivered by the get method:

.say while $_ = $*IN.get;

Here, the default variable $_ is used. This allows to omit creating the new variable and to make the whole program more compact. The .say call in it is a shortcut for $_.say.

← Miscellaneous | 96. The uniq utility →

95. The cat utility

Course navigation