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Programming-Idioms

  • C#
  • Go

Idiom #233 Read a command line string flag

Print the value of the flag -country passed to the program command line, or the default value "Canada" if no such flag was passed.

import "flag"
var country = flag.String("country", "Canada", "user home country")
flag.Parse()
fmt.Println("country is", *country)

country has pointer type *string.
Call Parse only once, after all flags are defined and before flags are read.
Flags must be passed before the non-flag arguments.
import static java.lang.System.out;
public static void main(String[] args) {
    String s;
    int i, n = args.length;
    for (i = 0; i < n; ++i)
        if (args[i].equals("-country"))
            break;
    s = ++i < n ? args[i] : "Canada";
    out.println(s);
}
New implementation...
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programming-idioms.org 
var country = flag.String("country", "Canada", "user home country")
flag.Parse()
fmt.Println("country is", *country)
public static void main(String[] args) {
    String s;
    int i, n = args.length;
    for (i = 0; i < n; ++i)
        if (args[i].equals("-country"))
            break;
    s = ++i < n ? args[i] : "Canada";
    out.println(s);
}
S := Application.GetOptionValue('country');
if S = '' then S := 'Canada';
writeln('Country = ',S);
my $country = 'Canada';
GetOptions("country=s" => \$country) or die("Error in command line args\n");
print "Country is $country\n";
parser = argparse.ArgumentParser()
parser.add_argument('-country', default='Canada', dest='country')
args = parser.parse_args()
print('country is', args.country)

try:
    i = argv.index('-country')
    print(argv[i + 1])
except:
    print('Canada')