Filter Files by Extension with `std.mem.endsWith()` in Zig

A robust and efficient way to detect .zig files when listing directory contents.

This recipe was written using Zig version 0.15.2. If this recipe is outdated, please let me know on X (@sepyke) or Bluesky (@pyk.sh).

Recently, I was building a simple library for my own, and in my build.zig I required to list all Zig files in an examples directory and build them as binaries. This recipe shows a robust and efficient way to detect .zig files using std.mem.endsWith().

When you’re iterating through directory contents, you often need to check if a file has a specific extension. Zig’s standard library provides std.mem.endsWith() which is perfect for this. It’s efficient and clear.

Here’s how you can use it to filter for .zig files:

filter_by_extension.zig

const std = @import("std");
const fs = std.fs;
const mem = std.mem;
const testing = std.testing;

pub fn main() !void {
    // For demonstration, we'll use a temporary directory.
    var tmp = testing.tmpDir(.{ .iterate = true });
    defer tmp.cleanup();
    const base_dir = tmp.dir;

    // Create some test files.
    try base_dir.writeFile(.{ .sub_path = "test.zig", .data = "// zig file" });
    try base_dir.writeFile(.{ .sub_path = "another.txt", .data = "just text" });
    try base_dir.writeFile(.{ .sub_path = "main.zig", .data = "// main zig file" });

    std.debug.print("Filtering for .zig files:\n", .{});

    var iter = base_dir.iterate();
    while (try iter.next()) |entry| {
        // Check if it's a file and ends with ".zig"
        if (entry.kind == .file and mem.endsWith(u8, entry.name, ".zig")) {
            std.debug.print("Found Zig file: {s}\n", .{entry.name});
        }
    }
}

Make sure Zig is installed:

Shell

$ zig version
0.15.2

Then run it:

Shell

$ zig run filter_by_extension.zig
Filtering for .zig files:
Found Zig file: test.zig
Found Zig file: main.zig

Filter Files by Extension with std.mem.endsWith() in Zig

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Filter Files by Extension with `std.mem.endsWith()` in Zig