diff --git a/README.md b/README.md
index 42502e8..21eeac1 100644
--- a/README.md
+++ b/README.md
@@ -57,6 +57,7 @@ For a list of applets, run `./pbui` or `./pbui -h`.  Currently supported applets
   - `du`
   - `uniq`
   - `shuf`
+  - `sha1`
 
 To run a given applet, use: `./pbui [APPLET] [arguments]`.
   
diff --git a/build.zig b/build.zig
index 664daec..651e019 100644
--- a/build.zig
+++ b/build.zig
@@ -32,6 +32,9 @@ pub fn build(b: *Builder) void {
     var rm_tests = b.addTest("src/rm.zig");
     rm_tests.setBuildMode(mode);
 
+    var sha1_tests = b.addTest("src/sha1.zig");
+    sha1_tests.setBuildMode(mode);
+
     const test_step = b.step("test", "Run library tests");
     test_step.dependOn(&main_tests.step);
     test_step.dependOn(&shuf_tests.step);
@@ -39,4 +42,5 @@ pub fn build(b: *Builder) void {
     test_step.dependOn(&false_tests.step);
     test_step.dependOn(&mkdir_tests.step);
     test_step.dependOn(&rm_tests.step);
+    test_step.dependOn(&sha1_tests.step);
 }
diff --git a/src/main.zig b/src/main.zig
index 592d43c..b309789 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -15,6 +15,7 @@ const std = @import("std");
 const du = @import("du.zig");
 const uniq = @import("uniq.zig");
 const shuf = @import("shuf.zig");
+const sha1 = @import("sha1.zig");
 const stdout = &std.io.getStdOut().outStream();
 const warn = std.debug.warn;
 const testing = std.testing;
@@ -40,6 +41,7 @@ pub fn usage(args: [][]u8) anyerror!u8 {
         \\du
         \\uniq
         \\shuf
+        \\sha1
         \\
     , .{});
 
@@ -75,6 +77,7 @@ pub fn main() anyerror!u8 {
     _ = try func_map.put("uniq", uniq.main);
     //_ = try func_map.put("ls", ls.main);
     _ = try func_map.put("shuf", shuf.main);
+    _ = try func_map.put("sha1", sha1.main);
 
     // check basename of exe
     var buffer: [100]u8 = undefined;
diff --git a/src/sha1.zig b/src/sha1.zig
new file mode 100644
index 0000000..32aa20e
--- /dev/null
+++ b/src/sha1.zig
@@ -0,0 +1,105 @@
+const std = @import("std");
+const Sha1 = std.crypto.Sha1;
+const opt = @import("opt.zig");
+const Allocator = std.mem.Allocator;
+const stdout = &std.io.getStdOut().outStream();
+const warn = std.debug.warn;
+const BUFSIZ = 4096;
+
+pub fn sha1(allocator: *Allocator, file: std.fs.File) ![40]u8 {
+    var h = Sha1.init();
+    var hash: [20]u8 = undefined;
+    var real_out: [40]u8 = undefined;
+
+    var file_buffer = std.ArrayList(u8).init(allocator);
+    defer file_buffer.deinit();
+
+    var read_buffer: [BUFSIZ]u8 = undefined;
+
+    var size = try file.readAll(&read_buffer);
+    while (size > 0) : (size = try file.readAll(&read_buffer)) {
+        try file_buffer.insertSlice(file_buffer.items.len, read_buffer[0..size]);
+    }
+    h.reset();
+    h.update(file_buffer.items[0..]);
+    h.final(hash[0..]);
+    var i: u8 = 0;
+    while (i < 20) : (i += 1) {
+        if (hash[i] <= 15) {
+            _ = try std.fmt.bufPrint(real_out[i * 2 ..], "0{x}", .{hash[i]});
+        } else {
+            _ = try std.fmt.bufPrint(real_out[i * 2 ..], "{x}", .{hash[i]});
+        }
+    }
+
+    return real_out;
+}
+
+const Sha1Flags = enum {
+    Help,
+    Version,
+};
+
+var flags = [_]opt.Flag(Sha1Flags){
+    .{
+        .name = Sha1Flags.Help,
+        .long = "help",
+    },
+    .{
+        .name = Sha1Flags.Version,
+        .long = "version",
+    },
+};
+
+pub fn main(args: [][]u8) anyerror!u8 {
+    var it = opt.FlagIterator(Sha1Flags).init(flags[0..], args);
+    while (it.next_flag() catch {
+        return 1;
+    }) |flag| {
+        switch (flag.name) {
+            Sha1Flags.Help => {
+                warn("sha1 [FILE_NAME ..]\n", .{});
+                return 1;
+            },
+            Sha1Flags.Version => {
+                warn("(version info here)\n", .{});
+                return 1;
+            },
+        }
+    }
+
+    var files = std.ArrayList([]u8).init(std.heap.page_allocator);
+    while (it.next_arg()) |file_name| {
+        try files.append(file_name);
+    }
+
+    if (files.items.len > 0) {
+        for (files.items) |file_name| {
+            const file = std.fs.cwd().openFile(file_name[0..], std.fs.File.OpenFlags{ .read = true, .write = false }) catch |err| {
+                try stdout.print("Error: cannot open file {}\n", .{file_name});
+                return 1;
+            };
+            // run command
+            var result = sha1(std.heap.page_allocator, file) catch |err| {
+                try stdout.print("Error: {}\n", .{err});
+                return 1;
+            };
+            try stdout.print("{}\n", .{result});
+            file.close();
+        }
+    } else {
+        var result = sha1(std.heap.page_allocator, std.io.getStdIn()) catch |err| {
+            try stdout.print("Error: {}\n", .{err});
+            return 1;
+        };
+        try stdout.print("{}\n", .{result});
+    }
+    return 0;
+}
+
+test "hash on license" {
+    var file = try std.fs.cwd().openFile("LICENSE", std.fs.File.OpenFlags{ .read = true });
+    var result = try sha1(std.heap.page_allocator, file);
+
+    std.debug.assert(std.mem.eql(u8, result[0..], "8624bcdae55baeef00cd11d5dfcfa60f68710a02"));
+}