Course of Raku / Objects, I/O, and exceptions / Input and output / Running external programs 🆕

run and shell

There are two ways to launch an external program. The run function takes the command and its arguments as separate values and runs the program directly, without involving a shell:

run 'echo', 'hello';

This runs the echo program with the single argument hello, which prints hello. Because the arguments are passed separately, there is no risk of the shell mis-interpreting spaces or special characters — run is the safe default.

The shell function instead passes a single string to the system shell, which interprets it. This lets you use shell features like pipes and redirection:

shell 'echo hello | tr a-z A-Z';

Here, the shell runs echo, pipes its output through tr, and prints HELLO. The convenience comes with a caution: because the shell parses the string, building a shell command from untrusted input is dangerous. Prefer run unless you specifically need shell features.

Both return a Proc object describing how the program finished. By default, the launched program shares your program’s output, so what it prints appears on screen. To capture that output instead, you ask for it — the subject of the next topic.

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