init

.github/workflows/ci.yml

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+name: CI
+
+on: [push, pull_request]
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: goto-bus-stop/setup-zig@v2
+      - run: zig build test
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: goto-bus-stop/setup-zig@v2
+      - run: zig fmt --check src/*.zig

.gitignore

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+zig-out/
+zig-cache/

README.md

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+# pc
+
+A simple tool for quickly calculating the percentage change between a set of numbers.
+
+## Usage
+
+## Installation

build.zig

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+const std = @import("std");
+
+// Although this function looks imperative, note that its job is to
+// declaratively construct a build graph that will be executed by an external
+// runner.
+pub fn build(b: *std.Build) void {
+    // Standard target options allows the person running `zig build` to choose
+    // what target to build for. Here we do not override the defaults, which
+    // means any target is allowed, and the default is native. Other options
+    // for restricting supported target set are available.
+    const target = b.standardTargetOptions(.{});
+
+    // Standard optimization options allow the person running `zig build` to select
+    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
+    // set a preferred release mode, allowing the user to decide how to optimize.
+    const optimize = b.standardOptimizeOption(.{});
+
+    const exe = b.addExecutable(.{
+        .name = "pc",
+        // In this case the main source file is merely a path, however, in more
+        // complicated build scripts, this could be a generated file.
+        .root_source_file = .{ .path = "src/main.zig" },
+        .target = target,
+        .optimize = optimize,
+    });
+
+    exe.strip = true;
+
+    // This declares intent for the executable to be installed into the
+    // standard location when the user invokes the "install" step (the default
+    // step when running `zig build`).
+    b.installArtifact(exe);
+
+    // This *creates* a Run step in the build graph, to be executed when another
+    // step is evaluated that depends on it. The next line below will establish
+    // such a dependency.
+    const run_cmd = b.addRunArtifact(exe);
+
+    // By making the run step depend on the install step, it will be run from the
+    // installation directory rather than directly from within the cache directory.
+    // This is not necessary, however, if the application depends on other installed
+    // files, this ensures they will be present and in the expected location.
+    run_cmd.step.dependOn(b.getInstallStep());
+
+    // This allows the user to pass arguments to the application in the build
+    // command itself, like this: `zig build run -- arg1 arg2 etc`
+    if (b.args) |args| {
+        run_cmd.addArgs(args);
+    }
+
+    // This creates a build step. It will be visible in the `zig build --help` menu,
+    // and can be selected like this: `zig build run`
+    // This will evaluate the `run` step rather than the default, which is "install".
+    const run_step = b.step("run", "Run the app");
+    run_step.dependOn(&run_cmd.step);
+
+    // Creates a step for unit testing. This only builds the test executable
+    // but does not run it.
+    const unit_tests = b.addTest(.{
+        .root_source_file = .{ .path = "src/main.zig" },
+        .target = target,
+        .optimize = optimize,
+    });
+
+    const run_unit_tests = b.addRunArtifact(unit_tests);
+
+    // Similar to creating the run step earlier, this exposes a `test` step to
+    // the `zig build --help` menu, providing a way for the user to request
+    // running the unit tests.
+    const test_step = b.step("test", "Run unit tests");
+    test_step.dependOn(&run_unit_tests.step);
+}

src/main.zig

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+const std = @import("std");
+const ArrayList = std.ArrayList;
+
+pub const EscapeCodes = struct {
+    pub const dim = "\x1b[2m";
+    pub const pink = "\x1b[38;5;205m";
+    pub const white = "\x1b[37m";
+    pub const red = "\x1b[31m";
+    pub const yellow = "\x1b[33m";
+    pub const green = "\x1b[32m";
+    pub const magenta = "\x1b[35m";
+    pub const cyan = "\x1b[36m";
+    pub const reset = "\x1b[0m";
+    pub const erase_line = "\x1b[2K\r";
+};
+
+const usage_text: []const u8 =
+    \\Usage:   pc [numbers...] or ... | pc
+    \\Options:
+    \\ -h, --help: Show this help message
+    \\
+;
+
+fn parseNum(s: []const u8) ?f32 {
+    const val = std.fmt.parseFloat(f32, s) catch {
+        std.debug.print("skipping invalid number: '{s}'\n", .{s});
+        return null;
+    };
+    return val;
+}
+
+fn percentDiff(a: f32, b: f32) f32 {
+    return (b - a) / a * 100.0;
+}
+
+fn fancyPrint(writer: anytype, diff: f32) !void {
+    const symbol = blk: {
+        if (diff > 0.0) {
+            try writer.print("{s}", .{EscapeCodes.green});
+            break :blk "↑";
+        } else if (diff < 0.0) {
+            try writer.print("{s}", .{EscapeCodes.red});
+            break :blk "↓";
+        } else {
+            try writer.print("{s}", .{EscapeCodes.white});
+            break :blk "→";
+        }
+    };
+    try writer.print("{s} {d: >6.2}%\n", .{ symbol, diff });
+}
+
+pub fn main() !void {
+    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+    defer arena.deinit();
+    const allocator = arena.allocator();
+    const stdout = std.io.getStdOut().writer();
+
+    const args = try std.process.argsAlloc(allocator);
+    var nums = ArrayList(f32).init(allocator);
+    defer nums.deinit();
+
+    // parse args
+    var arg_i: usize = 1;
+    while (arg_i < args.len) : (arg_i += 1) {
+        const arg = args[arg_i];
+        if (std.mem.eql(u8, arg, "-h") or std.mem.eql(u8, arg, "--help")) {
+            try stdout.writeAll(usage_text);
+            return std.process.cleanExit();
+        }
+        if (parseNum(arg)) |num| {
+            try nums.append(num);
+        }
+    }
+
+    // if no nums, read from stdin
+    if (nums.items.len == 0) {
+        var input = std.io.getStdIn().reader().readAllAlloc(allocator, 10 * 1024 * 1024) catch |e| {
+            std.debug.print("pc: error reading stdin: {s}\n", .{@errorName(e)});
+            return std.process.exit(1);
+        };
+        var it = std.mem.tokenizeAny(u8, input, " \t\n\r");
+        while (it.next()) |s| {
+            if (parseNum(s)) |num| {
+                try nums.append(num);
+            }
+        }
+    }
+
+    if (nums.items.len < 2) {
+        std.debug.print("pc: need at least 2 numbers\n", .{});
+        try stdout.writeAll(usage_text);
+        return std.process.exit(1);
+    }
+
+    // calculate percent difference between each pair
+    var cur = nums.items[0];
+    for (nums.items[1..]) |num| {
+        const diff = percentDiff(cur, num);
+        try fancyPrint(stdout, diff);
+        cur = num;
+    }
+}