diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 4d7234b2..5416122c 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -12,8 +12,8 @@ jobs:
       fail-fast: false
       matrix:
         go-version:
-        - '1.21.x'
         - '1.22.x'
+        - '1.23.x'
         os:
         - ubuntu-latest
         - macos-latest
@@ -33,7 +33,7 @@ jobs:
         go test -race ./...
 
     - name: Tidy
-      if: matrix.os == 'ubuntu-latest' && matrix.go-version == '1.22.x' # no need to do this everywhere
+      if: matrix.os == 'ubuntu-latest' && matrix.go-version == '1.23.x' # no need to do this everywhere
       run: |
         go mod tidy
 
diff --git a/README.md b/README.md
index bd1b79cb..f6703565 100644
--- a/README.md
+++ b/README.md
@@ -12,18 +12,17 @@ Contributions are welcome, but please open an issue for discussion first.
 
 Included are the following:
 
-- dirhash: calculate hashes over directory trees the same way that the Go tool does.
 - goproxytest: a GOPROXY implementation designed for test use.
 - gotooltest: Use the Go tool inside test scripts (see testscript below)
 - imports: list of known architectures and OSs, and support for reading import statements.
-- modfile: read and write `go.mod` files while preserving formatting and comments.
-- module: module paths and versions.
 - par: do work in parallel.
-- semver: semantic version parsing.
 - testenv: information on the current testing environment.
 - testscript: script-based testing based on txtar files
 - txtar: simple text-based file archives for testing.
 
+Note that most users of `txtar` should use https://pkg.go.dev/golang.org/x/tools/txtar instead.
+Our package will be replaced by it once https://github.com/golang/go/issues/59264 is fixed.
+
 ### testscript
 
 The most popular package here is the [testscript](https://pkg.go.dev/github.com/rogpeppe/go-internal/testscript) package:
diff --git a/go.mod b/go.mod
index 6b4304f2..58d0c9ef 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module github.com/rogpeppe/go-internal
 
-go 1.21
+go 1.22
 
 require (
 	golang.org/x/mod v0.18.0
diff --git a/goproxytest/proxy.go b/goproxytest/proxy.go
index d3fc975a..e8fe8a7c 100644
--- a/goproxytest/proxy.go
+++ b/goproxytest/proxy.go
@@ -24,6 +24,7 @@ package goproxytest
 import (
 	"archive/zip"
 	"bytes"
+	"cmp"
 	"encoding/json"
 	"fmt"
 	"io/fs"
@@ -76,12 +77,8 @@ func NewServer(dir, addr string) (*Server, error) {
 }
 
 func newServer(dir, addr string, logf func(string, ...any)) (*Server, error) {
-	if addr == "" {
-		addr = "localhost:0"
-	}
-	if dir == "" {
-		dir = "testmod"
-	}
+	addr = cmp.Or(addr, "localhost:0")
+	dir = cmp.Or(dir, "testmod")
 	srv := Server{dir: dir, logf: logf}
 	if err := srv.readModList(); err != nil {
 		return nil, fmt.Errorf("cannot read modules: %v", err)
diff --git a/imports/scan.go b/imports/scan.go
index e69e271e..dbed3553 100644
--- a/imports/scan.go
+++ b/imports/scan.go
@@ -85,6 +85,7 @@ Files:
 
 var ErrNoGo = fmt.Errorf("no Go source files")
 
+// TODO: replace with maps.Keys from go1.23
 func keys(m map[string]bool) []string {
 	var list []string
 	for k := range m {
diff --git a/internal/os/execpath/lp_unix.go b/internal/os/execpath/lp_unix.go
index 37f18c79..d233a1f5 100644
--- a/internal/os/execpath/lp_unix.go
+++ b/internal/os/execpath/lp_unix.go
@@ -7,6 +7,7 @@
 package execpath
 
 import (
+	"cmp"
 	"os"
 	"path/filepath"
 	"strings"
@@ -45,10 +46,8 @@ func Look(file string, getenv func(string) string) (string, error) {
 	}
 	path := getenv("PATH")
 	for _, dir := range filepath.SplitList(path) {
-		if dir == "" {
-			// Unix shell semantics: path element "" means "."
-			dir = "."
-		}
+		// Unix shell semantics: path element "" means "."
+		dir = cmp.Or(dir, ".")
 		path := filepath.Join(dir, file)
 		if err := findExecutable(path); err == nil {
 			return path, nil
diff --git a/testscript/exe.go b/testscript/exe.go
index 0ccd7738..9f9fdc14 100644
--- a/testscript/exe.go
+++ b/testscript/exe.go
@@ -75,7 +75,6 @@ func RunMain(m TestingM, commands map[string]func() int) (exitCode int) {
 
 		// We're not in a subcommand.
 		for name := range commands {
-			name := name
 			// Set up this command in the directory we added to $PATH.
 			binfile := filepath.Join(bindir, name)
 			if runtime.GOOS == "windows" {
diff --git a/testscript/testscript.go b/testscript/testscript.go
index 11460502..e4024837 100644
--- a/testscript/testscript.go
+++ b/testscript/testscript.go
@@ -320,7 +320,6 @@ func RunT(t T, p Params) {
 	refCount := int32(len(files))
 	names := make(map[string]bool)
 	for _, file := range files {
-		file := file
 		name := filepath.Base(file)
 		if name1, ok := strings.CutSuffix(name, ".txt"); ok {
 			name = name1
@@ -737,13 +736,13 @@ func (ts *TestScript) runLine(line string) (runOK bool) {
 			ts.Fatalf("unknown command %q", args[0])
 		}
 	}
-	ts.callBuiltinCmd(args[0], func() {
+	ts.callBuiltinCmd(func() {
 		cmd(ts, neg, args[1:])
 	})
 	return true
 }
 
-func (ts *TestScript) callBuiltinCmd(cmd string, runCmd func()) {
+func (ts *TestScript) callBuiltinCmd(runCmd func()) {
 	ts.runningBuiltin = true
 	defer func() {
 		r := recover()