change cpu speed linux zig

spd.zig

const std = @import("std");

pub fn put(b: []u8, a: []const u8) usize {
    @memcpy(b[0..a.len], a);
    return a.len;
}

pub fn main() u8 {
    var ally = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    defer ally.deinit();
    const args = std.os.argv;

    if (args.len < 3) return 1;

    var d = std.fs.cwd().openDir("/sys/devices/system/cpu/", .{}) catch return 2;
    defer d.close();

    const start, const end = b: {
        var b: [16]u8 = undefined;
        const sl = d.readFile("possible", &b) catch return 3;
        if (sl.len < 3) return 4;
        {
            var s = std.mem.splitAny(u8, sl, "\n-");
            break :b .{
                std.fmt.parseInt(u16, s.next() orelse return 5, 10) catch return 6,
                std.fmt.parseInt(u16, s.next() orelse return 5, 10) catch return 6,
            };
        }
    };

    if (end < start) return 7;

    var b: [32]u8 = undefined;
    for (start..end +| 1) |i| {
        var n: usize = put(&b, "cpu");
        n += std.fmt.formatIntBuf(b[3..], i, 10, .lower, .{});
        n += put(b[n..], "/cpufreq/");

        var cf_d = d.openDir(b[0..n], .{}) catch return 9;
        defer cf_d.close();

        if (args.len > 3) {
             cf_d.writeFile(.{
                .sub_path = "scaling_governor",
                 .data = std.mem.span(args[3]),
            }) catch return 11;
        }

        cf_d.writeFile(.{
            .sub_path = "scaling_min_freq",
            .data = std.mem.span(args[1]),
        }) catch return 12;

        cf_d.writeFile(.{
            .sub_path = "scaling_max_freq",
            .data = std.mem.span(args[2]),
        }) catch return 13;
    }

    return 0;
}