Args-M

Command-Line Arguments

Inferno has a dedicated module for processing commandline flags and arguments, arg(2).

Source

args.b:17,22

The module Arg is loaded and initialized. As per the manual, the arg->init() function must be called before any other functions can be called from Arg.

The usage message is also set pre-emptively for use later, if necessary.

args.b:24,37

There are two flag arguments, r and c which set reversal of arguments and the list item indicator mark, respectively.

The flag r is a binary option toggle, the flag's presence as an argument is sufficient to change the value of rev.

The flag c takes an argument. The arg->earg() function is used to pop the flag's argument out of the list. Specifically with regards to earg() rather than arg() as per the manual, earg() will call arg->usage() if the relevant argument does not exist.

Note: After the processing of all flags, argv is re-set from the value contained within arg to remove the elements (if any) utilized by flags and their arguments.

args.b:41,51

This section utilizes the rev variable to (naively) reverse the list argv. After the rev check, the list argv is printed in order from beginning to end with each element being printed on a new line with the mark variable being prefixed to the list element currently at the head of the argv list each iteration during printout.

Demo

; limbo args.b
; args -h
usage: args [-r] [-c mark] words...
; args a b c d
Argc after flags: 4
→  a
→  b
→  c
→  d
; args -r a b c d
Argc after flags: 4
→  d
→  c
→  b
→  a
; args -c 'quack: ' a b c d
Argc after flags: 4
quack:  a
quack:  b
quack:  c
quack:  d
; args -r -c '-> ' d c b a
Argc after flags: 4
->  a
->  b
->  c
->  d
; 

Exercises

• Can you trick earg() into accepting a nil value?
• How would you pull an int out of earg()?
• How would you trip the usage() message call-able from earg()?