This document provides tips for command line scripting in Perl 6. It discusses common command line switches like -e, -n, and -p. It explains that @*ARGS is an array of all arguments and $*ARGFILES treats arguments as file paths. MAIN subroutines can match signatures to arguments. Undocumented MAIN subs will output usage info generated from documentation tags. The document encourages using phasers, named argument parsing, and modules for larger scripts.

1. Perl 6 Command Line Scripting
A few tips

2. Hi
● Simon Proctor
● Scimon most places (Twitter etc)
● Senior Developer at Zoopla
● Addicted to Perl6

3. Command Line Switches
● -e : Same as -E in Perl5. Strict mode on and say works.
● -n : Runs the program with $_ set to each line in the given files. Note newlines
are stripped from the input lines.
● -p : As -n then say the value of $_ (calls gist on the value and adds a newline).
● -I path : Adds the path for module searches.
● -M module : Loads the given module prior to running the script.
Not included -0, -a, -C, -d, -D, -E, -f, -F, -i, -l, -M-, -s, -S, -t, -T, -u, -U, -X
Also available PERL6LIB environment variable useful when using prove

4. @*ARGS and $*ARGFILES
● @*ARGS is an Array of all the arguments passed to the programme.
● All arguments are type Str but the Array itself is not typed.
● $*ARGFILES is an IO::CatHandle (actually IO::ArgFiles) object that treats
all the values in @*ARGS as paths to files and allows you to iterate over all of them.
● $*ARGFILES is lazily evaluated. It will throw an Exception if the paths do not
exist.
● $*ARGFILES is set to $*IN if there are no arguments passed.

5. Welcome to MAIN
multi sub MAIN( *@files ) {...}
multi sub MAIN( $file1, $file2 ) {...}
multi sub MAIN( :$s(size) ) {...}
● @*ARGS is mapped into a signature with a few things to bear in mind
○ All inputs a Str typed but if they match a numeric format they may be a subtype :
■ IntStr, RatStr, ComplexStr, NumStr all are both their appropriate types as required
● Named parameters will be either a Scalar or an Array depending on the
number of times they are called.
● Named parameters can also be stored in a slurpy hash *%args.

6. Auto documentation
● Default response to no matching signature is to call the USAGE sub.
● If you want to call the USAGE sub you need to provide one.
● Default is to output the $*USAGE string.
○ Created by reading documentation on all MAIN subs.
○ #| attaches before the thing being documented
○ #= attached after the thing being documented
○ Both are POD directives and will be included in the documentation
○ To discount a MAIN sub from the $*USAGE string creation give it the trait is
hidden-from-USAGE

7. Auto documentation : Example
multi sub MAIN( :$h? ) is hidden-from-USAGE {
USAGE();
}
multi sub MAIN( :$h!, *@ ) is hidden-from-USAGE {
USAGE();
}
#| Sum up some numbers
multi sub MAIN(
*@nums #= A list of numbers
) {
say [+] @nums;
}
sub USAGE() {
say "Highly useful summing thing";
say $*USAGE;
}
Highly useful summing thing
Usage:
doc.pl6 [<nums> ...] -- Sum up some numbers
[<nums> ...] A list of numbers

8. Tips and Tricks
● END and BEGIN phasers and state variables can be very useful with -n and -p
● my %*SUB-MAIN-OPTS = :named-anywhere;
○ Allows named arguments anywhere in the parsing order.
● subtype Single of Any where * !~~ Positional;
○ Use on a named parameter to ensure only one can be passed.
● Subsets::IO includes a number of useful predefined IO subsets
○ E.G. IO::Path::dw for a writable directory
● For larger scripts move the core code into a module and use you script as a
launcher