cat takes filename args

cat/build.zig

@@ -0,0 +1,27 @@
+const Builder = @import("std").build.Builder;
+
+pub fn build(b: *Builder) 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 release options allow the person running `zig build` to select
+    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall.
+    const mode = b.standardReleaseOptions();
+
+    const exe = b.addExecutable("cat", "src/main.zig");
+    exe.setTarget(target);
+    exe.setBuildMode(mode);
+    exe.install();
+
+    const run_cmd = exe.run();
+    run_cmd.step.dependOn(b.getInstallStep());
+    if (b.args) |args| {
+        run_cmd.addArgs(args);
+    }
+
+    const run_step = b.step("run", "Run the app");
+    run_step.dependOn(&run_cmd.step);
+}

cat/src/main.zig

@@ -0,0 +1,82 @@
+const std = @import("std");
+const page_allocator = std.heap.page_allocator;
+const format = std.fmt.format;
+const Allocator = std.mem.Allocator;
+const File = std.fs.File;
+const ArrayList = std.ArrayList;
+const stdout = std.io.getStdOut();
+
+pub fn main() !void {
+    var mem_root = std.heap.GeneralPurposeAllocator(.{}){};
+    defer _ = mem_root.deinit();
+
+    try run(&mem_root.allocator);
+}
+
+fn run(mem: *Allocator) !void {
+    const stdin = std.io.getStdIn();
+    const stderr = std.io.getStdErr();
+
+    var handles = ArrayList(File).init(mem);
+    defer handles.deinit();
+
+    defer {
+        for (handles.items) |f| {
+            f.close();
+        }
+    }
+
+    var args = std.process.args();
+    defer args.deinit();
+
+    var path_buffer: [std.fs.MAX_PATH_BYTES]u8 = undefined;
+
+    _ = args.skip();
+    while (args.next(mem)) |maybe| {
+        const arg = try maybe;
+        defer mem.free(arg);
+
+        if (std.mem.eql(u8, arg, "-")) {
+            try handles.append(stdin);
+        } else {
+            const path = std.fs.realpath(arg, &path_buffer) catch |err| {
+                stderr.writer().print("Path Error with path {}: {}\n", .{ arg, err }) catch {};
+                std.os.exit(1);
+            };
+            const f = std.fs.openFileAbsolute(path, .{ .read = true }) catch |err| {
+                stderr.writer().print("Open Error with path {}: {}\n", .{ arg, err }) catch {};
+                std.os.exit(1);
+            };
+            const fi = try f.stat();
+            if (fi.kind != .File) {
+                stderr.writer().print("File at path {} is not regular file, is: {}\n", .{ arg, fi.kind }) catch {};
+                std.os.exit(1);
+            }
+            try handles.append(f);
+        }
+    }
+
+    const page = try page_allocator.alloc(u8, std.mem.page_size);
+    defer page_allocator.free(page);
+
+    if (handles.items.len == 0) {
+        try dump(page, stdin);
+        return;
+    }
+
+    for (handles.items) |f| {
+        try dump(page, f);
+    }
+}
+
+// dump dumps a file to stdout, utilizing the provided page of memory as a
+// transfer buffer.
+fn dump(page: []u8, f: File) !void {
+    while (true) {
+        var n = try f.read(page);
+        if (n <= 0) {
+            return;
+        }
+        _ = try stdout.write(page[0..n]);
+    }
+}