Course of Raku / Objects, I/O, and exceptions / Input and output / Running external programs 🆕 / Exercises / Pass a variable to a child

Solution: Pass a variable to a child

Here is a possible solution to the task.

Code

my $file = 'notes.txt';
spurt $file, "one\ntwo\nthree\n";

%*ENV<NOTES> = $file;

my $proc = shell 'wc -l < "$NOTES"', :out;
say $proc.out.slurp(:close).trim;

unlink $file;

🦋 You can find the source code in the file read-env.raku.

Output

3

Comments

  1. spurt creates notes.txt with three lines. Setting %*ENV<NOTES> to its name puts the file name into the environment that any child program will inherit.

  2. The shell command inherits that environment, expands $NOTES to notes.txt, and feeds the file into wc -l, which counts its lines. The < "$NOTES" redirection keeps the output to just the number 3, which we capture with :out and trim.

  3. Finally the clean-up is done back in Raku with unlink — no shell needed. Deleting the file is a plain file-system operation, so there is no reason to launch another process for it.

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