Myrddin has support in the standard library for command-line argument parsing.
cmd = std.optparse(args, &[
.argdesc = "words…",
.opts = [
[.opt='r', .desc = "reverse output"],
[.opt='m', .arg = "mark", .desc = "list items with prefix 'mark'"],
[.opt='T', .arg = "period", .desc = "set print sleep delay to 'period' ms"],
][:]
])
The cmd variable is assigned a std.optparsed type struct via the std.optparse() function.
The definitions provided in this block will be used for flag parsing later and for formatting the usage message provided by the library-provided -h and -? flags.
This usage will look like:
usage: ./out [-h?r] [-m mark] [-T period] words…
-h print this help message
-? print this help message
-r reverse output
-m mark list items with prefix 'mark'
-T period set print sleep delay to 'period' ms
for opt : cmd.opts
match opt
| ('r', ""):
reverse = true
| ('m', arg):
mark = arg
This section shows the beginning of the iteration, in order, of the flag (option) arguments to the program.
Each argument is matched against for parsing.
The r flag does not take an argument as indicated by the "" in the match case.
The m flag takes an argument as indicated by the presence of the name arg in the match case.
| ('T', arg):
match std.intparse(arg)
| `std.Some v:
delay = v * std.Msec
| `std.None:
std.fatal("err: invalid argument for period\n")
;;
A byte slice argument is parsed into a number and assigned to a pre-existing variable.
This section reverses, in-place, the cmd.args slice.
The cmd.args slice is the set of arguments which were not consumed by the preceding flag-type arguments.
This section prints a mark and argument from the cmd.args slice, in order, sleeping for a given period delay after each print.
; mbld -b out args.myr && ./out -h && ./out -r -m '«' -T 500 -- -ß A b C d E
<out -h && ./out -r -m '«' -T 500 -- -ß A b C d E
usage: ./out [-h?r] [-m mark] [-T period] words…
-h print this help message
-? print this help message
-r reverse output
-m mark list items with prefix 'mark'
-T period set print sleep delay to 'period' ms
« E
« d
« C
« b
« A
« -ß
;