Idiomatic way to implement standard Unix behaviour of using STDIN if no files are specified on the command line? - raku

Question

Is there a more elegant way of processing input coming from either the command line arguments or STDIN if no files were given on the command line? I'm currently doing it like this:
sub MAIN(*#opt-files, Bool :$debug, ... other named options ...) {
# note that parentheses are mandatory here for some reason
my $input = #opt-files ?? ([~] .IO.slurp for #opt-files) !! $*IN.slurp;
... process $input ...
}
and it's not too bad, but I wonder if I'm missing some simpler way of doing it?

Answer 1

I would probably go for a multi sub MAIN, something like:
multi sub MAIN(Bool :$debug)
{
process-input($*IN.slurp);
}
multi sub MAIN(*#opt-files, Bool :$debug)
{
process-input($_.IO.slurp) for #opt-files;
}

Answer 2

I'd probably do two things to change this. I'd break up the ?? !! onto different lines, and I'd go for a full method chain:
sub MAIN(*#opt-files, Bool :$debug, ... other named options ...) {
my $input = #opt-files
?? #opt-files».IO».slurp.join
!! $*IN.slurp;
... process $input ...
}
You can also map it by using #opt-files.map(*.IO.slurp).join
Edit: building on ugexe's answer, you could do
sub MAIN(*#opt-files, Bool :$debug, ... other named options ...) {
# Default to $*IN if not files
#opt-files ||= '-';
my $input = #opt-files».IO».slurp.join
... process $input ...
}

Answer 3

Something that I might expect to work is to set #*ARGS to the list of file names in the signature.
And then just use $*ARGFILES.
sub MAIN( *#*ARGS, Bool :$debug, ... other named options ...) {
my $input = slurp; # implicitly calls $*ARGFILES.slurp()
... process $input ...
}
It doesn't work though.
You could get Rakudo to update $*ARGFILES by nulling it with a low-level null before you use it.
sub MAIN( *#*ARGS, Bool :$debug, ... other named options ...) {
{ use nqp; $*ARGFILES := nqp::null }
my $input = slurp;
... process $input ...
}
But that is using an implementation detail that may change in the future.
A better way is to just directly create a new instance of IO::ArgFiles yourself.
You can even store it in $*ARGFILES. Then slurp on its own would slurp in all of the file contents.
sub MAIN( *#opt-files, Bool :$debug, ... other named options ...) {
my $*ARGFILES = IO::ArgFiles.new( #opt-files || $*IN );
my $input = slurp;
... process $input ...
}
Note that IO::ArgFiles is just an empty subclass of IO::CatHandle.
So you could write IO::CatHandle.new( #opt‑files || $*IN ) instead.