zig-clap

A simple and easy to use command line argument parser library for Zig.

Installation

Developers tend to either use

• The latest tagged release of Zig
• The latest build of Zigs master branch

Depending on which developer you are, you need to run different zig fetch commands:

# Version of zig-clap that works with a tagged release of Zig
# Replace `<REPLACE ME>` with the version of zig-clap that you want to use
# See: https://github.com/Hejsil/zig-clap/releases
zig fetch --save https://github.com/Hejsil/zig-clap/archive/refs/tags/<REPLACE ME>.tar.gz

# Version of zig-clap that works with latest build of Zigs master branch
zig fetch --save git+https://github.com/Hejsil/zig-clap

Then add the following to build.zig:

const clap = b.dependency("clap", .{});
exe.root_module.addImport("clap", clap.module("clap"));

Features

• Short arguments -a
  • Chaining -abc where a and b does not take values.
  • Multiple specifications are tallied (e.g. -v -v).
• Long arguments --long
• Supports both passing values using spacing and = (-a 100, -a=100)
  • Short args also support passing values with no spacing or = (-a100)
  • This all works with chaining (-ba 100, -ba=100, -ba100)
• Supports options that can be specified multiple times (-e 1 -e 2 -e 3)
• Print help message from parameter specification.
• Parse help message to parameter specification.

API Reference

Automatically generated API Reference for the project can be found at https://Hejsil.github.io/zig-clap. Note that Zig autodoc is in beta; the website may be broken or incomplete.

Examples

clap.parse

The simplest way to use this library is to just call the clap.parse function.

const clap = @import("clap");
const std = @import("std");

const debug = std.debug;
const io = std.io;

pub fn main() !void {
    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    defer _ = gpa.deinit();

    // First we specify what parameters our program can take.
    // We can use `parseParamsComptime` to parse a string into an array of `Param(Help)`
    const params = comptime clap.parseParamsComptime(
        \\-h, --help             Display this help and exit.
        \\-n, --number <usize>   An option parameter, which takes a value.
        \\-s, --string <str>...  An option parameter which can be specified multiple times.
        \\<str>...
        \\
    );

    // Initialize our diagnostics, which can be used for reporting useful errors.
    // This is optional. You can also pass `.{}` to `clap.parse` if you don't
    // care about the extra information `Diagnostics` provides.
    var diag = clap.Diagnostic{};
    var res = clap.parse(clap.Help, &params, clap.parsers.default, .{
        .diagnostic = &diag,
        .allocator = gpa.allocator(),
    }) catch |err| {
        // Report useful error and exit
        diag.report(io.getStdErr().writer(), err) catch {};
        return err;
    };
    defer res.deinit();

    if (res.args.help != 0)
        debug.print("--help\n", .{});
    if (res.args.number) |n|
        debug.print("--number = {}\n", .{n});
    for (res.args.string) |s|
        debug.print("--string = {s}\n", .{s});
    for (res.positionals) |pos|
        debug.print("{s}\n", .{pos});
}

The result will contain an args field and a positionals field. args will have one field for each none positional parameter of your program. The name of the field will be the longest name of the parameter.

The fields in args are typed. The type is based on the name of the value the parameter takes. Since --number takes a usize the field res.args.number has the type usize.

Note that this is only the case because clap.parsers.default has a field called usize which contains a parser that returns usize. You can pass in something other than clap.parsers.default if you want some other mapping.

const clap = @import("clap");
const std = @import("std");

const debug = std.debug;
const io = std.io;
const process = std.process;

pub fn main() !void {
    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    defer _ = gpa.deinit();

    // First we specify what parameters our program can take.
    // We can use `parseParamsComptime` to parse a string into an array of `Param(Help)`
    const params = comptime clap.parseParamsComptime(
        \\-h, --help             Display this help and exit.
        \\-n, --number <INT>     An option parameter, which takes a value.
        \\-a, --answer <ANSWER>  An option parameter which takes an enum.
        \\-s, --string <STR>...  An option parameter which can be specified multiple times.
        \\<FILE>...
        \\
    );

    // Declare our own parsers which are used to map the argument strings to other
    // types.
    const YesNo = enum { yes, no };
    const parsers = comptime .{
        .STR = clap.parsers.string,
        .FILE = clap.parsers.string,
        .INT = clap.parsers.int(usize, 10),
        .ANSWER = clap.parsers.enumeration(YesNo),
    };

    var diag = clap.Diagnostic{};
    var res = clap.parse(clap.Help, &params, parsers, .{
        .diagnostic = &diag,
        .allocator = gpa.allocator(),
        // The assignment separator can be configured. `--number=1` and `--number:1` is now
        // allowed.
        .assignment_separators = "=:",
    }) catch |err| {
        diag.report(io.getStdErr().writer(), err) catch {};
        return err;
    };
    defer res.deinit();

    if (res.args.help != 0)
        debug.print("--help\n", .{});
    if (res.args.number) |n|
        debug.print("--number = {}\n", .{n});
    if (res.args.answer) |a|
        debug.print("--answer = {s}\n", .{@tagName(a)});
    for (res.args.string) |s|
        debug.print("--string = {s}\n", .{s});
    for (res.positionals) |pos|
        debug.print("{s}\n", .{pos});
}

streaming.Clap

The streaming.Clap is the base of all the other parsers. It's a streaming parser that uses an args.Iterator to provide it with arguments lazily.

const clap = @import("clap");
const std = @import("std");

const debug = std.debug;
const io = std.io;
const process = std.process;

pub fn main() !void {
    const allocator = std.heap.page_allocator;

    // First we specify what parameters our program can take.
    const params = [_]clap.Param(u8){
        .{
            .id = 'h',
            .names = .{ .short = 'h', .long = "help" },
        },
        .{
            .id = 'n',
            .names = .{ .short = 'n', .long = "number" },
            .takes_value = .one,
        },
        .{ .id = 'f', .takes_value = .one },
    };

    var iter = try process.ArgIterator.initWithAllocator(allocator);
    defer iter.deinit();

    // Skip exe argument
    _ = iter.next();

    // Initialize our diagnostics, which can be used for reporting useful errors.
    // This is optional. You can also leave the `diagnostic` field unset if you
    // don't care about the extra information `Diagnostic` provides.
    var diag = clap.Diagnostic{};
    var parser = clap.streaming.Clap(u8, process.ArgIterator){
        .params = &params,
        .iter = &iter,
        .diagnostic = &diag,
    };

    // Because we use a streaming parser, we have to consume each argument parsed individually.
    while (parser.next() catch |err| {
        // Report useful error and exit
        diag.report(io.getStdErr().writer(), err) catch {};
        return err;
    }) |arg| {
        // arg.param will point to the parameter which matched the argument.
        switch (arg.param.id) {
            'h' => debug.print("Help!\n", .{}),
            'n' => debug.print("--number = {s}\n", .{arg.value.?}),

            // arg.value == null, if arg.param.takes_value == .none.
            // Otherwise, arg.value is the value passed with the argument, such as "-a=10"
            // or "-a 10".
            'f' => debug.print("{s}\n", .{arg.value.?}),
            else => unreachable,
        }
    }
}

Currently, this parser is the only parser that allows an array of Param that is generated at runtime.

help

The help prints a simple list of all parameters the program can take. It expects the Id to have a description method and an value method so that it can provide that in the output. HelpOptions is passed to help to control how the help message is printed.

const clap = @import("clap");
const std = @import("std");

pub fn main() !void {
    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    defer _ = gpa.deinit();

    const params = comptime clap.parseParamsComptime(
        \\-h, --help     Display this help and exit.
        \\-v, --version  Output version information and exit.
        \\
    );

    var res = try clap.parse(clap.Help, &params, clap.parsers.default, .{
        .allocator = gpa.allocator(),
    });
    defer res.deinit();

    // `clap.help` is a function that can print a simple help message. It can print any `Param`
    // where `Id` has a `describtion` and `value` method (`Param(Help)` is one such parameter).
    // The last argument contains options as to how `help` should print those parameters. Using
    // `.{}` means the default options.
    if (res.args.help != 0)
        return clap.help(std.io.getStdErr().writer(), clap.Help, &params, .{});
}

$ zig-out/bin/help --help
    -h, --help
            Display this help and exit.

    -v, --version
            Output version information and exit.

usage

The usage prints a small abbreviated version of the help message. It expects the Id to have a value method so it can provide that in the output.

const clap = @import("clap");
const std = @import("std");

pub fn main() !void {
    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    defer _ = gpa.deinit();

    const params = comptime clap.parseParamsComptime(
        \\-h, --help         Display this help and exit.
        \\-v, --version      Output version information and exit.
        \\    --value <str>  An option parameter, which takes a value.
        \\
    );

    var res = try clap.parse(clap.Help, &params, clap.parsers.default, .{
        .allocator = gpa.allocator(),
    });
    defer res.deinit();

    // `clap.usage` is a function that can print a simple help message. It can print any `Param`
    // where `Id` has a `value` method (`Param(Help)` is one such parameter).
    if (res.args.help != 0)
        return clap.usage(std.io.getStdErr().writer(), clap.Help, &params);
}

$ zig-out/bin/usage --help
[-hv] [--value <str>]