diff --git a/env.go b/env.go
new file mode 100644
index 0000000..1e96e83
--- /dev/null
+++ b/env.go
@@ -0,0 +1,131 @@
+package env
+
+import (
+	"os"
+	"strings"
+)
+
+// Clear removes all environment variables.
+func Clear() {
+	os.Clearenv()
+}
+
+// Get returns the value of the environment variable with the given name.  If the
+// variable is not set an empty string is returned.
+//
+// To differentiate between a variable that is not set and a variable that is set to
+// an empty string, use the `Lookup` function.
+//
+// # parameters
+//
+//	name string   // the name of the environment variable
+//
+// # returns
+//
+//	string   // the value of the environment variable
+func Get(name string) string {
+	return os.Getenv(name)
+}
+
+// GetVars returns a map of environment variables.  If no variable names are provided
+// all environment variables are returned.  If variable names are provided, only
+// those variables are returned (if set).
+//
+// # parameters
+//
+//	names ...string   // (optional) names of environment variables to return;
+//	                 // if no names are provided the returned map contains all
+//	                 // environment variables.
+//
+// If a name is provided that is not set in the environment it is not included in
+// the returned map.
+//
+// # returns
+//
+//	Vars   // a map of environment variables
+//
+// The returned map is a `map[string]string` where the key is the name of the
+// environment variable and the value is the value of the environment variable.
+//
+// If no environment variables are set or all specified variables names are not set,
+// the returned map is empty.
+func GetVars(names ...string) Vars {
+	var result Vars
+
+	switch len(names) {
+	case 0: // all environment variables
+		result = make(Vars, 100)
+		env := os.Environ()
+		for _, s := range env {
+			k, v, _ := strings.Cut(s, "=")
+			result[k] = v
+		}
+	default: // only the named variables (if set)
+		result = make(Vars, len(names))
+		for _, k := range names {
+			if v, ok := os.LookupEnv(k); ok {
+				result[k] = v
+			}
+		}
+	}
+
+	return result
+}
+
+// Lookup returns the value of the environment variable with the given name and a
+// boolean indicating whether the variable is set.  If the variable is not set the
+// returned value is an empty string and the boolean is `false`.
+//
+// If you do not need to differentiate between a variable that is not set and a
+// variable that is set to an empty string, use the `Get` function.
+//
+// # parameters
+//
+//	name string   // the name of the environment variable
+//
+// # returns
+//
+//	string   // the value of the environment variable
+//
+//	bool     // true if the variable is set, false otherwise
+func Lookup(name string) (string, bool) {
+	return os.LookupEnv(name)
+}
+
+// Set sets the value of the environment variable with the given name.  If the variable
+// does not exist it is created.
+//
+// # parameters
+//
+//	name  string   // the name of the environment variable
+//
+//	value string   // the value to set
+//
+// # returns
+//
+//	error   // any error that occurs while setting the environment variable
+func Set(name, value string) error {
+	return os.Setenv(name, value)
+}
+
+// Unset removes the environment variables with the given names.  If a variable does
+// not exist (already not set) it is ignored.
+//
+// # parameters
+//
+//	names ...string   // the names of the environment variables to remove
+//
+// # returns
+//
+//	error   // any error that occurs while unsetting the environment variables
+//
+// On Unix systems (including Linux and macOS) the error is always `nil`, but
+// on Windows systems the error may be non-nil.
+func Unset(name ...string) error {
+	for _, k := range name {
+		if err := osUnsetenv(k); err != nil {
+			return err
+		}
+	}
+	return nil
+}
diff --git a/env_test.go b/env_test.go
new file mode 100644
index 0000000..dd690c8
--- /dev/null
+++ b/env_test.go
@@ -0,0 +1,184 @@
+package env
+
+import (
+	"errors"
+	"os"
+	"testing"
+
+	"github.com/blugnu/test"
+)
+
+func TestClear(t *testing.T) {
+	// ARRANGE
+	defer State().Reset()
+	os.Setenv("VAR", "value")
+
+	// ACT
+	Clear()
+
+	// ASSERT
+	_, isSet := os.LookupEnv("VAR")
+	test.IsFalse(t, isSet)
+}
+
+func TestGet(t *testing.T) {
+	// ARRANGE
+	defer State().Reset()
+	os.Clearenv()
+	os.Setenv("VAR", "value")
+
+	// ACT
+	result := Get("VAR")
+
+	// ASSERT
+	test.That(t, result, "variable present").Equals("value")
+
+	// ACT
+	result = Get("NOTSET")
+
+	// ASSERT
+	test.That(t, result, "variable not present").Equals("")
+}
+
+func TestGetVars(t *testing.T) {
+	// ARRANGE
+	testcases := []struct {
+		scenario string
+		exec     func(t *testing.T)
+	}{
+		{scenario: "all variables",
+			exec: func(t *testing.T) {
+				// ARRANGE
+				defer State().Reset()
+				os.Clearenv()
+				os.Setenv("VAR1", "value1")
+				os.Setenv("VAR2", "value2")
+
+				// ACT
+				result := GetVars()
+
+				// ASSERT
+				test.Map(t, result).Equals(Vars{"VAR1": "value1", "VAR2": "value2"})
+			},
+		},
+		{scenario: "specified variables (including ones not set)",
+			exec: func(t *testing.T) {
+				// ARRANGE
+				defer State().Reset()
+				os.Clearenv()
+				os.Setenv("VAR1", "value1")
+				os.Setenv("VAR2", "value2")
+
+				// ACT
+				result := GetVars("VAR1", "VAR3")
+
+				// ASSERT
+				test.Map(t, result).Equals(Vars{"VAR1": "value1"})
+			},
+		},
+	}
+	for _, tc := range testcases {
+		t.Run(tc.scenario, func(t *testing.T) {
+			tc.exec(t)
+		})
+	}
+}
+
+func TestLookup(t *testing.T) {
+	// ARRANGE
+	defer State().Reset()
+	os.Clearenv()
+	os.Setenv("VAR", "value")
+
+	// ACT
+	result, ok := Lookup("VAR")
+
+	// ASSERT
+	test.That(t, result, "variable present").Equals("value")
+	test.IsTrue(t, ok, "variable present")
+
+	// ACT
+	result, ok = Lookup("NOTSET")
+
+	// ASSERT
+	test.That(t, result, "variable not present").Equals("")
+	test.IsFalse(t, ok, "variable not present")
+}
+
+func TestSet(t *testing.T) {
+	// ARRANGE
+	defer State().Reset()
+	os.Clearenv()
+
+	// ACT
+	err := Set("VAR1", "value1")
+
+	// ASSERT
+	test.That(t, err).IsNil()
+	test.That(t, os.Getenv("VAR1")).Equals("value1")
+}
+
+func TestUnset(t *testing.T) {
+	// ARRANGE
+	testEnv := map[string]string{
+		"VAR1": "value1",
+		"VAR2": "value2",
+	}
+	testcases := []struct {
+		scenario string
+		exec     func(t *testing.T)
+	}{
+		{scenario: "no names specified",
+			exec: func(t *testing.T) {
+				// ACT
+				err := Unset()
+
+				// ASSERT
+				test.That(t, err).IsNil()
+				test.That(t, os.Getenv("VAR1")).Equals("value1")
+				test.That(t, os.Getenv("VAR2")).Equals("value2")
+			},
+		},
+		{scenario: "name specified",
+			exec: func(t *testing.T) {
+				// ACT
+				err := Unset("VAR1")
+
+				// ASSERT
+				test.That(t, err).IsNil()
+				_, isSet := os.LookupEnv("VAR1")
+				test.IsFalse(t, isSet)
+				test.That(t, os.Getenv("VAR2")).Equals("value2")
+			},
+		},
+		{
+			scenario: "error when unsetting",
+			exec: func(t *testing.T) {
+				// ARRANGE
+				unseterr := errors.New("unset error")
+				defer test.Using(&osUnsetenv, func(string) error { return unseterr })()
+
+				// ACT
+				err := Unset("VAR1", "VAR2")
+
+				// ASSERT
+				test.Error(t, err).Is(unseterr)
+				test.That(t, os.Getenv("VAR1")).Equals("value1")
+				test.That(t, os.Getenv("VAR2")).Equals("value2")
+			},
+		},
+	}
+	for _, tc := range testcases {
+		t.Run(tc.scenario, func(t *testing.T) {
+			// ARRANGE
+			defer State().Reset()
+			os.Clearenv()
+			for k, v := range testEnv {
+				os.Setenv(k, v)
+			}
+
+			// ACT & ASSERT
+			tc.exec(t)
+		})
+	}
+}
diff --git a/errors.go b/errors.go
new file mode 100644
index 0000000..67eee40
--- /dev/null
+++ b/errors.go
@@ -0,0 +1,157 @@
+package env
+
+import (
+	"errors"
+	"fmt"
+)
+
+var (
+	ErrNotSet            = errors.New("not set")
+	ErrSetVariableFailed = errors.New("set variable failed")
+)
+
+// ParseError is an error that wraps an error occurring while
+// parsing an environment variable.  It includes the name of the
+// variable being parsed at the time of the error.
+type ParseError struct {
+	VariableName string
+	Err          error
+}
+
+// Error returns a string representation of the error in the form:
+//
+//	env.ParseError: <variable name>: <error>
+//
+// If the VariableName field is empty:
+//
+//	env.ParseError: <error>
+//
+// If the Err field is nil:
+//
+//	env.ParseError: <variable name>
+//
+// If both fields are empty:
+//
+//	env.ParseError
+func (e ParseError) Error() string {
+	type when struct{ hasName, hasError bool }
+	fn := map[when]func() string{
+		{false, false}: func() string { return "env.ParseError" },
+		{false, true}:  func() string { return "env.ParseError: " + e.Err.Error() },
+		{true, false}:  func() string { return fmt.Sprintf("env.ParseError: %v", e.VariableName) },
+		{true, true}:   func() string { return fmt.Sprintf("env.ParseError: %v: %v", e.VariableName, e.Err) },
+	}
+	return fn[when{e.VariableName != "", e.Err != nil}]()
+}
+
+// Is reports whether the target error is a match for the receiver.
+// To be a match, the target must:
+//
+//   - be a ParseError
+//   - the target VariableName must match the receiver's VariableName,
+//     or be empty
+//   - the target Err field must satisfy errors.Is with respect to the
+//     receiver Err, or be nil
+func (e ParseError) Is(target error) bool {
+	if target, ok := target.(ParseError); ok {
+		return (target.VariableName == "" || e.VariableName == target.VariableName) &&
+			(target.Err == nil || errors.Is(e.Err, target.Err))
+	}
+	return false
+}
+
+// Unwrap returns the error that caused the env.Parse.
+func (e ParseError) Unwrap() error {
+	return e.Err
+}
+
+// InvalidValueError is an error type that represents an invalid value.  The Value
+// field contains the invalid value, and the Err field contains the error that
+// caused the value to be invalid.
+type InvalidValueError struct {
+	Value string
+	Err   error
+}
+
+// Error returns a string representation of the error in the form:
+//
+//	env.InvalidValueError: <value>: <error>
+//
+// If the Value field is empty:
+//
+//	env.InvalidValueError: <error>
+//
+// If the Err field is nil:
+//
+//	env.InvalidValueError: <value>
+//
+// If both fields are empty:
+//
+//	env.InvalidValueError
+func (e InvalidValueError) Error() string {
+	type when struct{ hasValue, hasError bool }
+	fn := map[when]func() string{
+		{false, false}: func() string { return "env.InvalidValueError" },
+		{false, true}:  func() string { return "env.InvalidValueError: " + e.Err.Error() },
+		{true, false}:  func() string { return fmt.Sprintf("env.InvalidValueError: %v", e.Value) },
+		{true, true}:   func() string { return fmt.Sprintf("env.InvalidValueError: %v: %v", e.Value, e.Err) },
+	}
+	return fn[when{e.Value != "", e.Err != nil}]()
+}
+
+// Is reports whether the target error is a match for the receiver.
+// To be a match, the target must:
+//
+//   - be an InvalidValueError
+//   - the target Value field must match the receiver's Value, or be empty
+//   - the target Err field must satisfy errors.Is with respect to the receiver Err,
+//     or be nil
+func (e InvalidValueError) Is(target error) bool {
+	if target, ok := target.(InvalidValueError); ok {
+		return (target.Value == "" || e.Value == target.Value) &&
+			(target.Err == nil || errors.Is(e.Err, target.Err))
+	}
+	return false
+}
+
+// Unwrap returns the error that caused the invalid value error.
+func (e InvalidValueError) Unwrap() error {
+	return e.Err
+}
+
+// RangeError is an error type that represents a value that is out of range; Min and
+// Max fields identify the range of valid values.
+//
+// If Min and Max are both the zero value of T, the error represents a general out-of-range
+// error with no identified range.
+type RangeError[T comparable] struct {
+	Min T
+	Max T
+}
+
+// Error returns a string representation of the error in the form:
+//
+//	out of range: <Min> <= (x) <= <Max>
+//
+// If Min and Max are both the zero value of T:
+//
+//	out of range
+func (e RangeError[T]) Error() string {
+	if e == (RangeError[T]{}) {
+		return "env.RangeError"
+	}
+	return fmt.Sprintf("env.RangeError: %v <= (x) <= %v", e.Min, e.Max)
+}
+
+// Is reports whether the target error is a match for the receiver.
+// To be a match, the target must:
+//
+//   - be a RangeError
+//   - the target Min and Max fields must match the receiver's Min and Max fields,
+//     or be the zero value of T
+func (e RangeError[T]) Is(target error) bool {
+	if target, ok := target.(RangeError[T]); ok {
+		return e == target || (target == RangeError[T]{})
+	}
+	return false
+}
diff --git a/errors_test.go b/errors_test.go
new file mode 100644
index 0000000..5a54807
--- /dev/null
+++ b/errors_test.go
@@ -0,0 +1,331 @@
+package env
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/blugnu/test"
+)
+
+func TestParseError_Error(t *testing.T) {
+	// ARRANGE
+	testcases := []struct {
+		scenario string
+		varname  string
+		err      error
+		assert   func(t *testing.T, result string)
+	}{
+		{scenario: "with VariableName and Err",
+			varname: "VAR",
+			err:     errors.New("some error"),
+			assert: func(t *testing.T, result string) {
+				test.That(t, result).Equals("env.ParseError: VAR: some error")
+			},
+		},
+		{scenario: "with VariableName and nil Err",
+			varname: "VAR",
+			assert: func(t *testing.T, result string) {
+				test.That(t, result).Equals("env.ParseError: VAR")
+			},
+		},
+		{scenario: "with empty VariableName and Err",
+			err: errors.New("some error"),
+			assert: func(t *testing.T, result string) {
+				test.That(t, result).Equals("env.ParseError: some error")
+			},
+		},
+		{scenario: "with empty VariableName and nil Err",
+			assert: func(t *testing.T, result string) {
+				test.That(t, result).Equals("env.ParseError")
+			},
+		},
+	}
+	for _, tc := range testcases {
+		t.Run(tc.scenario, func(t *testing.T) {
+			// ARRANGE
+			sut := ParseError{
+				VariableName: tc.varname,
+				Err:          tc.err,
+			}
+
+			// ACT
+			result := sut.Error()
+
+			// ASSERT
+			tc.assert(t, result)
+		})
+	}
+}
+
+func TestParseError_Is(t *testing.T) {
+	// ARRANGE
+	sut := ParseError{
+		VariableName: "VAR",
+		Err:          errors.New("some error"),
+	}
+	testcases := []struct {
+		scenario string
+		target   error
+		assert   func(t *testing.T, result bool)
+	}{
+		{scenario: "target: non-ParseError",
+			target: errors.New("some error"),
+			assert: func(t *testing.T, result bool) {
+				test.Bool(t, result).IsFalse()
+			},
+		},
+		{scenario: "target: zero-value ParseError",
+			target: ParseError{},
+			assert: func(t *testing.T, result bool) {
+				test.Bool(t, result).IsTrue()
+			},
+		},
+		{scenario: "target: ParseError with different VariableName",
+			target: ParseError{VariableName: "OTHER", Err: errors.New("some error")},
+			assert: func(t *testing.T, result bool) {
+				test.Bool(t, result).IsFalse()
+			},
+		},
+		{scenario: "target: ParseError with different Err",
+			target: ParseError{VariableName: "VAR", Err: errors.New("other error")},
+			assert: func(t *testing.T, result bool) {
+				test.Bool(t, result).IsFalse()
+			},
+		},
+		{scenario: "target: ParseError with same VariableName and Err",
+			target: ParseError{VariableName: "VAR", Err: sut.Err},
+			assert: func(t *testing.T, result bool) {
+				test.Bool(t, result).IsTrue()
+			},
+		},
+	}
+	for _, tc := range testcases {
+		t.Run(tc.scenario, func(t *testing.T) {
+			// ACT
+			result := sut.Is(tc.target)
+
+			// ASSERT
+			tc.assert(t, result)
+		})
+	}
+}
+
+func TestParseError_Unwrap(t *testing.T) {
+	// ARRANGE
+	sut := ParseError{
+		VariableName: "VAR",
+		Err:          errors.New("some error"),
+	}
+
+	// ACT
+	result := sut.Unwrap()
+
+	// ASSERT
+	test.Value(t, result).Equals(sut.Err)
+}
+
+func TestInvalidValueError_Error(t *testing.T) {
+	// ARRANGE
+	testcases := []struct {
+		scenario string
+		value    string
+		err      error
+		assert   func(t *testing.T, result string)
+	}{
+		{scenario: "with Value and Err",
+			value: "VAL",
+			err:   errors.New("some error"),
+			assert: func(t *testing.T, result string) {
+				test.That(t, result).Equals("env.InvalidValueError: VAL: some error")
+			},
+		},
+		{scenario: "with Value and nil Err",
+			value: "VAL",
+			assert: func(t *testing.T, result string) {
+				test.That(t, result).Equals("env.InvalidValueError: VAL")
+			},
+		},
+		{scenario: "with empty Value and Err",
+			err: errors.New("some error"),
+			assert: func(t *testing.T, result string) {
+				test.That(t, result).Equals("env.InvalidValueError: some error")
+			},
+		},
+		{scenario: "with empty Value and nil Err",
+			assert: func(t *testing.T, result string) {
+				test.That(t, result).Equals("env.InvalidValueError")
+			},
+		},
+	}
+	for _, tc := range testcases {
+		t.Run(tc.scenario, func(t *testing.T) {
+			// ARRANGE
+			sut := InvalidValueError{
+				Value: tc.value,
+				Err:   tc.err,
+			}
+
+			// ACT
+			result := sut.Error()
+
+			// ASSERT
+			tc.assert(t, result)
+		})
+	}
+}
+
+func TestInvalidValueError_Is(t *testing.T) {
+	// ARRANGE
+	sut := InvalidValueError{
+		Value: "VAL",
+		Err:   errors.New("some error"),
+	}
+	testcases := []struct {
+		scenario string
+		target   error
+		assert   func(t *testing.T, result bool)
+	}{
+		{scenario: "target: non-InvalidValueError",
+			target: errors.New("some error"),
+			assert: func(t *testing.T, result bool) {
+				test.Bool(t, result).IsFalse()
+			},
+		},
+		{scenario: "target: zero-value InvalidValueError",
+			target: InvalidValueError{},
+			assert: func(t *testing.T, result bool) {
+				test.Bool(t, result).IsTrue()
+			},
+		},
+		{scenario: "target: InvalidValueError with different Value",
+			target: InvalidValueError{Value: "OTHER", Err: errors.New("some error")},
+			assert: func(t *testing.T, result bool) {
+				test.Bool(t, result).IsFalse()
+			},
+		},
+		{scenario: "target: InvalidValueError with different Err",
+			target: InvalidValueError{Value: "VAL", Err: errors.New("other error")},
+			assert: func(t *testing.T, result bool) {
+				test.Bool(t, result).IsFalse()
+			},
+		},
+		{scenario: "target: InvalidValueError with same Value and Err",
+			target: InvalidValueError{Value: "VAL", Err: sut.Err},
+			assert: func(t *testing.T, result bool) {
+				test.Bool(t, result).IsTrue()
+			},
+		},
+	}
+	for _, tc := range testcases {
+		t.Run(tc.scenario, func(t *testing.T) {
+			// ACT
+			result := sut.Is(tc.target)
+
+			// ASSERT
+			tc.assert(t, result)
+		})
+	}
+}
+
+func TestInvalidValueError_Unwrap(t *testing.T) {
+	// ARRANGE
+	sut := InvalidValueError{
+		Value: "VAL",
+		Err:   errors.New("some error"),
+	}
+
+	// ACT
+	result := sut.Unwrap()
+
+	// ASSERT
+	test.Value(t, result).Equals(sut.Err)
+}
+
+func TestRangeError_Error(t *testing.T) {
+	// ARRANGE
+	testcases := []struct {
+		scenario string
+		min      int
+		max      int
+		assert   func(t *testing.T, result string)
+	}{
+		{scenario: "with Min and Max",
+			min: 1,
+			max: 10,
+			assert: func(t *testing.T, result string) {
+				test.That(t, result).Equals("env.RangeError: 1 <= (x) <= 10")
+			},
+		},
+		{scenario: "with zero Min and Max",
+			assert: func(t *testing.T, result string) {
+				test.That(t, result).Equals("env.RangeError")
+			},
+		},
+	}
+	for _, tc := range testcases {
+		t.Run(tc.scenario, func(t *testing.T) {
+			// ARRANGE
+			sut := RangeError[int]{
+				Min: tc.min,
+				Max: tc.max,
+			}
+
+			// ACT
+			result := sut.Error()
+
+			// ASSERT
+			tc.assert(t, result)
+		})
+	}
+}
+
+func TestRangeError_Is(t *testing.T) {
+	// ARRANGE
+	sut := RangeError[int]{Min: 1, Max: 10}
+
+	testcases := []struct {
+		scenario string
+		target   error
+		assert   func(t *testing.T, result bool)
+	}{
+		{scenario: "target: non-RangeError",
+			target: errors.New("some error"),
+			assert: func(t *testing.T, result bool) {
+				test.Bool(t, result).IsFalse()
+			},
+		},
+		{scenario: "target: zero-value RangeError",
+			target: RangeError[int]{},
+			assert: func(t *testing.T, result bool) {
+				test.Bool(t, result).IsTrue()
+			},
+		},
+		{scenario: "target: RangeError with different Min",
+			target: RangeError[int]{Min: 2, Max: 10},
+			assert: func(t *testing.T, result bool) {
+				test.Bool(t, result).IsFalse()
+			},
+		},
+		{scenario: "target: RangeError with different Max",
+			target: RangeError[int]{Min: 1, Max: 20},
+			assert: func(t *testing.T, result bool) {
+				test.Bool(t, result).IsFalse()
+			},
+		},
+		{scenario: "target: RangeError with same Min and Max",
+			target: RangeError[int]{Min: 1, Max: 10},
+			assert: func(t *testing.T, result bool) {
+				test.Bool(t, result).IsTrue()
+			},
+		},
+	}
+	for _, tc := range testcases {
+		t.Run(tc.scenario, func(t *testing.T) {
+			// ACT
+			result := sut.Is(tc.target)
+
+			// ASSERT
+			tc.assert(t, result)
+		})
+	}
+}
diff --git a/funcs.go b/funcs.go
new file mode 100644
index 0000000..d5d0922
--- /dev/null
+++ b/funcs.go
@@ -0,0 +1,11 @@
+package env
+
+import "os"
+
+// function variables to facilitate testing
+var (
+	osLookupEnv = os.LookupEnv
+	osReadFile  = os.ReadFile
+	osSetenv    = os.Setenv
+	osUnsetenv  = os.Unsetenv
+)
diff --git a/load.go b/load.go
new file mode 100644
index 0000000..58e8a74
--- /dev/null
+++ b/load.go
@@ -0,0 +1,121 @@
+package env
+
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+	"os"
+	"strings"
+)
+
+// Load loads environment variables from one or more files.  Files should be formatted as a list
+// of key-value pairs, one per line, separated by an equals sign. Lines that are empty or start
+// with a hash (#) are ignored.
+//
+// # example file format
+//
+//	# this is a comment
+//	NAME1=value1
+//	NAME2=value2
+//
+//	# this is another comment
+//	NAME3=value3
+//
+// # parameters
+//
+//	files: ...string    // 0..n file path(s)
+//
+// # returns
+//
+//	error      // an error that wraps all errors that occurred while loading variables;
+//	           // if no errors occurred the result is nil
+//
+// The joined errors will be in the order that the files were specified and will be wrapped
+// with the file path that caused the error:
+//
+//	"path/to/file: error"
+//
+// # .env file
+//
+// The function will always attempt to load variables from a ".env" file.
+//
+// If ".env" (or "./.env") is included in the files parameter it will be loaded
+// in the order specified relative to other files; if the ".env" file does not exist
+// an error will be included in the returned error.
+//
+// If ".env" is not explicitly specified it will be loaded before any other files, if it
+// exists; if it does not exist it is ignored without error.
+//
+// If no files are specified the function will attempt to load variables from ".env"
+// and will return an error if the file does not exist.
+//
+// # example: loading .env:
+//
+//	if err := Load(); err != nil {
+//		log.Fatal(err) // possibly because .env does not exist
+//	}
+//
+// # example: loading .env and a specified file:
+//
+//	if err := Load("test.env"); err != nil {
+//		log.Fatal(err) // will not be because .env did not exist; could be because test.env does not exist
+//	}
+func Load(files ...string) error {
+	// determine if ".env" has been explicitly specified and if it is required
+	filenames := map[string]bool{}
+	for _, f := range files {
+		filenames[f] = true
+	}
+	dotenvRequired := len(filenames) == 0 || (filenames[".env"] || filenames["./.env"])
+
+	// if ".env" has not been explicitly specified we will load it before loading
+	// any other files
+	if !filenames["./.env"] && !filenames[".env"] {
+		files = append([]string{".env"}, files...)
+	}
+
+	// we will be collecting any errors that occur while loading the files
+	errs := []error{}
+
+	for _, filename := range files {
+		err := loadFile(filename)
+		if err == nil {
+			continue
+		}
+		if !dotenvRequired && (filename == ".env" || filename == "./.env") && errors.Is(err, fs.ErrNotExist) {
+			continue
+		}
+		errs = append(errs, fmt.Errorf("%s: %w", filename, err))
+	}
+
+	return errors.Join(errs...)
+}
+
+// loadFile loads environment variables from a file. The file should be formatted as a list of
+// key-value pairs, one per line, separated by an equals sign. Lines that are empty or start with
+// a hash (#) are ignored.
+//
+// # parameters
+//
+//	path: string   // the path to the file to loadFile
+//
+// # returns
+//
+//	error          // any error that occurrs while loading or applying variables
+func loadFile(path string) error {
+	bytes, err := osReadFile(path)
+	if err != nil {
+		return err
+	}
+	errs := []error{}
+	for _, line := range strings.Split(string(bytes), "\n") {
+		if line = strings.TrimSpace(line); line == "" || line[0] == '#' {
+			continue
+		}
+		parts := strings.SplitN(line, "=", 2)
+		vname := strings.TrimSpace(parts[0])
+		value := strings.TrimSpace(parts[1])
+		errs = append(errs, os.Setenv(vname, value))
+	}
+	return errors.Join(errs...)
+}
diff --git a/load_test.go b/load_test.go
new file mode 100644
index 0000000..cae46a1
--- /dev/null
+++ b/load_test.go
@@ -0,0 +1,244 @@
+package env
+
+import (
+	"errors"
+	"io/fs"
+	"os"
+	"testing"
+
+	"github.com/blugnu/test"
+)
+
+func TestLoad(t *testing.T) {
+	// ARRANGE
+	testcases := []struct {
+		scenario string
+		args     []any
+		exec     func(t *testing.T)
+	}{
+		{scenario: "no arguments/.env exists",
+			exec: func(t *testing.T) {
+				// ARRANGE
+				readsDotEnv := false
+				defer State().Reset()
+				defer test.Using(&osReadFile, func(path string) ([]byte, error) {
+					readsDotEnv = readsDotEnv || path == ".env"
+					return []byte("VAR1=loaded-value-1\nVAR2=loaded-value-2"), nil
+				})()
+				os.Clearenv()
+				os.Setenv("VAR1", "env-value")
+
+				// ACT
+				err := Load()
+
+				// ASSERT
+				test.That(t, err).IsNil()
+				test.IsTrue(t, readsDotEnv)
+				test.That(t, os.Getenv("VAR1")).Equals("loaded-value-1")
+				test.That(t, os.Getenv("VAR2")).Equals("loaded-value-2")
+			},
+		},
+		{scenario: "no arguments/.env does not exist",
+			exec: func(t *testing.T) {
+				// ARRANGE
+				defer State().Reset()
+				defer test.Using(&osReadFile, func(string) ([]byte, error) {
+					return nil, os.ErrNotExist
+				})()
+				os.Clearenv()
+				os.Setenv("VAR1", "env-value")
+
+				// ACT
+				err := Load()
+
+				// ASSERT
+				test.Error(t, err).Is(os.ErrNotExist)
+				test.That(t, os.Getenv("VAR1")).Equals("env-value")
+			},
+		},
+		{scenario: ".env argument/.env does not exist",
+			exec: func(t *testing.T) {
+				// ARRANGE
+				defer State().Reset()
+				defer test.Using(&osReadFile, func(string) ([]byte, error) {
+					return nil, os.ErrNotExist
+				})()
+				os.Clearenv()
+				os.Setenv("VAR1", "env-value")
+
+				// ACT
+				err := Load(".env")
+
+				// ASSERT
+				test.Error(t, err).Is(os.ErrNotExist)
+				test.That(t, os.Getenv("VAR1")).Equals("env-value")
+			},
+		},
+		{scenario: "file path argument/valid file/.env does not exist",
+			exec: func(t *testing.T) {
+				// ARRANGE
+				filesLoaded := []string{}
+				defer State().Reset()
+				defer test.Using(&osReadFile, func(path string) ([]byte, error) {
+					filesLoaded = append(filesLoaded, path)
+					switch path {
+					case ".env":
+						return nil, fs.ErrNotExist
+					case "test.env":
+						return []byte("VAR1=loaded-value-1\nVAR2=loaded-value-2"), nil
+					default:
+						panic("unexpected file path: " + path)
+					}
+				})()
+				os.Clearenv()
+				os.Setenv("VAR1", "env-value")
+
+				// ACT
+				err := Load("test.env")
+
+				// ASSERT
+				test.That(t, err).IsNil()
+				test.Slice(t, filesLoaded).Equals([]string{".env", "test.env"})
+				test.That(t, os.Getenv("VAR1")).Equals("loaded-value-1")
+				test.That(t, os.Getenv("VAR2")).Equals("loaded-value-2")
+			},
+		},
+		{scenario: "file path argument/valid file/.env exists",
+			exec: func(t *testing.T) {
+				// ARRANGE
+				filesLoaded := []string{}
+				defer State().Reset()
+				defer test.Using(&osReadFile, func(path string) ([]byte, error) {
+					filesLoaded = append(filesLoaded, path)
+					switch path {
+					case ".env":
+						return []byte("VAR3=dotenv-value-3"), nil
+					case "test.env":
+						return []byte("VAR1=loaded-value-1\nVAR2=loaded-value-2"), nil
+					default:
+						panic("unexpected file path: " + path)
+					}
+				})()
+				os.Clearenv()
+				os.Setenv("VAR1", "env-value")
+
+				// ACT
+				err := Load("test.env")
+
+				// ASSERT
+				test.That(t, err).IsNil()
+				test.That(t, filesLoaded).Equals([]string{".env", "test.env"})
+				test.That(t, os.Getenv("VAR1")).Equals("loaded-value-1")
+				test.That(t, os.Getenv("VAR2")).Equals("loaded-value-2")
+				test.That(t, os.Getenv("VAR3")).Equals("dotenv-value-3")
+			},
+		},
+		{scenario: "file path argument/valid file/.env error",
+			exec: func(t *testing.T) {
+				// ARRANGE
+				dotenverr := errors.New("error reading .env")
+				filesLoaded := []string{}
+				defer State().Reset()
+				defer test.Using(&osReadFile, func(path string) ([]byte, error) {
+					filesLoaded = append(filesLoaded, path)
+					switch path {
+					case ".env":
+						return nil, dotenverr
+					case "test.env":
+						return []byte("VAR1=loaded-value-1\nVAR2=loaded-value-2"), nil
+					default:
+						panic("unexpected file path: " + path)
+					}
+				})()
+				os.Clearenv()
+				os.Setenv("VAR1", "env-value")
+
+				// ACT
+				err := Load("test.env")
+
+				// ASSERT
+				test.Error(t, err).Is(dotenverr)
+				test.That(t, filesLoaded).Equals([]string{".env", "test.env"})
+				test.That(t, os.Getenv("VAR1")).Equals("loaded-value-1")
+				test.That(t, os.Getenv("VAR2")).Equals("loaded-value-2")
+			},
+		},
+		{scenario: "explicit .env/before other files",
+			exec: func(t *testing.T) {
+				// ARRANGE
+				filesLoaded := []string{}
+				defer State().Reset()
+				defer test.Using(&osReadFile, func(path string) ([]byte, error) {
+					filesLoaded = append(filesLoaded, path)
+					switch path {
+					case ".env":
+						return []byte("VAR=dotenv-value"), nil
+					case "test.env":
+						return []byte("VAR=test-value"), nil
+					default:
+						panic("unexpected file path: " + path)
+					}
+				})()
+				os.Clearenv()
+				os.Setenv("VAR", "env-value")
+
+				// ACT
+				err := Load(".env", "test.env")
+
+				// ASSERT
+				test.That(t, err).IsNil()
+				test.That(t, filesLoaded).Equals([]string{".env", "test.env"})
+				test.That(t, os.Getenv("VAR")).Equals("test-value")
+			},
+		},
+		{scenario: "explicit .env/after other files",
+			exec: func(t *testing.T) {
+				// ARRANGE
+				filesLoaded := []string{}
+				defer State().Reset()
+				defer test.Using(&osReadFile, func(path string) ([]byte, error) {
+					filesLoaded = append(filesLoaded, path)
+					switch path {
+					case ".env":
+						return []byte("VAR=dotenv-value"), nil
+					case "test.env":
+						return []byte("VAR=test-value"), nil
+					default:
+						panic("unexpected file path: " + path)
+					}
+				})()
+				os.Clearenv()
+				os.Setenv("VAR", "env-value")
+
+				// ACT
+				err := Load("test.env", ".env")
+
+				// ASSERT
+				test.That(t, err).IsNil()
+				test.That(t, filesLoaded).Equals([]string{"test.env", ".env"})
+				test.That(t, os.Getenv("VAR")).Equals("dotenv-value")
+			},
+		},
+	}
+	for _, tc := range testcases {
+		t.Run(tc.scenario, func(t *testing.T) {
+			tc.exec(t)
+		})
+	}
+}
+
+func TestLoadFile_WithEmptyLinesAndComments(t *testing.T) {
+	// ARRANGE
+	defer State().Reset()
+	defer test.Using(&osReadFile, func(string) ([]byte, error) {
+		return []byte("VAR1=value-1\n\n# comment\nVAR2=value-2=with-equals"), nil
+	})()
+
+	// ACT
+	err := loadFile("test.env")
+
+	// ASSERT
+	test.That(t, err).IsNil()
+	test.That(t, os.Getenv("VAR1")).Equals("value-1")
+	test.That(t, os.Getenv("VAR2")).Equals("value-2=with-equals")
+}
diff --git a/parse.go b/parse.go
new file mode 100644
index 0000000..7c3e4ac
--- /dev/null
+++ b/parse.go
@@ -0,0 +1,98 @@
+package env
+
+// ConversionFunc is a function that converts a string to a value of type T.
+// It is the type of the conversion function used by the Parse and Override
+// functions.
+//
+// # parameters
+//
+//	string string   // the string to convert
+//
+// # returns
+//
+//	T       // the converted value
+//
+//	error   // any error that occurs during conversion
+type ConversionFunc[T any] func(string) (T, error)
+
+// Override replaces the current value of some variable with the value obtained
+// by parsing a named environment variable. If the named environment variable is
+// not set, the target variable is not modified.
+//
+// If an error occurs during parsing or conversion, the target variable is not
+// modified and the error is returned.
+//
+// The function returns true if the target variable was modified from its
+// original value, false otherwise.
+//
+// # parameters
+//
+//	dest *T                       // a pointer to the variable to be changed
+//
+//	name string                   // the name of the environment variable to parse
+//
+//	cnv func(string) (T, error)   // a function to parse the environment variable
+//
+// # returns
+//
+//	bool    // true if the target variable was modified, false otherwise
+//
+//	error   // any error resulting from parsing the named environment variable
+//
+// The bool result should not be relied on to determine whether an error occurred;
+// The function will return false when:
+//
+//   - an error occurs parsing or converting the named environment variable
+//   - the named environment variable is not set
+//   - the named environment variable is set with a value that is successfully
+//     parsed and converted to yield the same value as currently held in the
+//     destination variable.
+//
+// Only the error result can determine if an error occurred.
+func Override[T comparable](dest *T, name string, cnv func(string) (T, error)) (bool, error) {
+	v, err := Parse(name, cnv)
+	switch {
+	case err == nil && *dest != v:
+		*dest = v
+		return true, nil
+	default:
+		return false, err
+	}
+}
+
+// Parse parses the environment variable with the given name and returns a value of
+// type T, obtained by passing the value of the environment variable to a provided
+// conversion function.
+//
+// # parameters
+//
+//	name string             // the name of the environment variable to parse
+//
+//	cnv ConversionFunc[T]   // a function to parse the environment variable;
+//	                        // the function should return a value of type T and
+//	                        // an error if the value cannot be converted
+//
+// # returns
+//
+//	T       // the value of the environment variable; if an error occurs the
+//	        // zero value of T is returned
+//
+//	error   // any error resulting from parsing the environment variable;
+//	        // if the error is ErrNotSet a nil error is returned
+//
+// # conversion functions
+//
+// The `as` package provides a number of conversion functions that can be used with
+// this function.  For example, to parse an integer environment variable:
+//
+//	value, err := env.Parse("MY_INT_VAR", as.Int)
+func Parse[T any](name string, cnv ConversionFunc[T]) (T, error) {
+	if v, ok := osLookupEnv(name); ok {
+		r, err := cnv(v)
+		if err != nil {
+			return *new(T), ParseError{VariableName: name, Err: InvalidValueError{Value: v, Err: err}}
+		}
+		return r, nil
+	}
+	return *new(T), ParseError{VariableName: name, Err: ErrNotSet}
+}
diff --git a/parse_test.go b/parse_test.go
new file mode 100644
index 0000000..237adfc
--- /dev/null
+++ b/parse_test.go
@@ -0,0 +1,100 @@
+package env
+
+import (
+	"errors"
+	"os"
+	"strconv"
+	"testing"
+
+	"github.com/blugnu/test"
+)
+
+func TestParse(t *testing.T) {
+	// ARRANGE
+	defer test.Using(&osLookupEnv, func(string) (string, bool) {
+		return "123", true
+	})()
+
+	// ACT
+	value, err := Parse("VAR", strconv.Atoi)
+
+	// ASSERT
+	test.That(t, value).Equals(123)
+	test.That(t, err).IsNil()
+}
+
+func TestParse_WhenVariableNotSet(t *testing.T) {
+	// ARRANGE
+	defer test.Using(&osLookupEnv, func(string) (string, bool) {
+		return "", false
+	})()
+
+	// ACT
+	value, err := Parse("NOT_SET", func(s string) (string, error) { return s, nil })
+
+	// ASSERT
+	test.That(t, value).Equals("")
+	test.Error(t, err).Is(ErrNotSet)
+}
+
+func TestParse_WhenConversionFails(t *testing.T) {
+	// ARRANGE
+	converr := errors.New("conversion error")
+	defer test.Using(&osLookupEnv, func(string) (string, bool) {
+		return "not-a-number", true
+	})()
+
+	// ACT
+	value, err := Parse("NOT_A_NUMBER", func(s string) (int, error) { return 0, converr })
+
+	// ASSERT
+	test.That(t, value).Equals(0)
+	test.Error(t, err).Is(InvalidValueError{Value: "not-a-number", Err: converr})
+}
+
+func TestOverride(t *testing.T) {
+	// ARRANGE
+	var value = 42
+	defer State().Reset()
+	os.Clearenv()
+	os.Setenv("VAR", "123")
+
+	// ACT
+	result, err := Override(&value, "VAR", strconv.Atoi)
+
+	// ASSERT
+	test.That(t, err).IsNil()
+	test.IsTrue(t, result)
+	test.That(t, value).Equals(123)
+}
+
+func TestOverride_WhenValueIsNotChanged(t *testing.T) {
+	// ARRANGE
+	var value = 123
+	defer State().Reset()
+	os.Clearenv()
+	os.Setenv("VAR", "123")
+
+	// ACT
+	result, err := Override(&value, "VAR", strconv.Atoi)
+
+	// ASSERT
+	test.That(t, err).IsNil()
+	test.IsFalse(t, result)
+	test.That(t, value).Equals(123)
+}
+
+func TestOverride_WhenVariableIsNotSet(t *testing.T) {
+	// ARRANGE
+	var value = 42
+	defer State().Reset()
+	os.Clearenv()
+
+	// ACT
+	result, err := Override(&value, "VAR", strconv.Atoi)
+
+	// ASSERT
+	test.Error(t, err).Is(ErrNotSet)
+	test.IsFalse(t, result)
+	test.That(t, value).Equals(42)
+}
diff --git a/state.go b/state.go
new file mode 100644
index 0000000..b7cc4ad
--- /dev/null
+++ b/state.go
@@ -0,0 +1,67 @@
+package env
+
+import (
+	"os"
+	"strings"
+)
+
+// state represents the state of all environment variables captured at
+// a point in time.  It is used to reset the environment to a known
+// state, typically after a test has modified the environment.
+type state []string
+
+// State captures the current state of the environment variables. It
+// is typically used to capture the state before a test modifies the
+// environment so that it can be reset to the original state after
+// the test has run (by deferring a call to the Reset method on the
+// returned state value).
+//
+// # returns
+//
+//	state   // the current state of the environment variables
+//
+// The state is captured using os.Environ().
+//
+// # example
+//
+//	func TestSomething(t *testing.T) {
+//		// ARRANGE
+//		defer env.State().Reset()
+//		env.Vars{
+//			"VAR1", "value1",
+//			"VAR2", "value2",
+//		}.Set()
+//
+//		// ACT
+//		// ...
+//	}
+func State() state {
+	return os.Environ()
+}
+
+// Reset resets the environment variables to the state captured when
+// the State function was called.
+//
+// This function is typically used in a defer statement to ensure the
+// environment is reset after a test has modified the environment.
+//
+// # example
+//
+//	func TestSomething(t *testing.T) {
+//		// ARRANGE
+//		defer env.State().Reset()
+//		env.Vars{
+//			"VAR1", "value1",
+//			"VAR2", "value2",
+//		}.Set()
+//
+//		// ACT
+//		// ...
+//	}
+func (s state) Reset() {
+	os.Clearenv()
+	for _, e := range s {
+		k, v, _ := strings.Cut(e, "=")
+		os.Setenv(k, v)
+	}
+}
diff --git a/state_test.go b/state_test.go
new file mode 100644
index 0000000..6ad4642
--- /dev/null
+++ b/state_test.go
@@ -0,0 +1,44 @@
+package env
+
+import (
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/blugnu/test"
+)
+
+func TestState(t *testing.T) {
+	// ARRANGE
+	env := os.Environ()
+
+	// ACT
+	result := State()
+
+	// ASSERT
+	test.Slice(t, result).Equals(env)
+}
+
+func TestState_Reset(t *testing.T) {
+	// ARRANGE
+	og := os.Environ()
+	defer func() {
+		os.Clearenv()
+		for _, s := range og {
+			k, v, _ := strings.Cut(s, "=")
+			os.Setenv(k, v)
+		}
+	}()
+
+	os.Clearenv()
+
+	// ACT
+	state{
+		"VAR1=value1",
+		"VAR2=value2",
+	}.Reset()
+
+	// ASSERT
+	test.That(t, os.Getenv("VAR1")).Equals("value1")
+	test.That(t, os.Getenv("VAR2")).Equals("value2")
+}
diff --git a/vars.go b/vars.go
new file mode 100644
index 0000000..a29f089
--- /dev/null
+++ b/vars.go
@@ -0,0 +1,53 @@
+package env
+
+import (
+	"slices"
+	"strings"
+)
+
+// Vars is a map of environment variables.
+type Vars map[string]string
+
+// Names returns the names of all variables in the map as a sorted slice.
+func (v Vars) Names() []string {
+	names := make([]string, 0, len(v))
+	for k := range v {
+		names = append(names, k)
+	}
+	slices.Sort(names)
+	return names
+}
+
+// Set applies the variables to the environment.  If an error occurs while setting
+// a variable, the error is returned without any further variables being set.
+//
+// # returns
+//
+//	error   // any error that occurs while setting the variables
+func (v Vars) Set() error {
+	for k, v := range v {
+		if err := osSetenv(k, v); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// String returns a string representation of the variables. The result is a string of
+// comma delimited NAME="VALUE" entries, sorted by NAME and enclosed in [-]'s.
+//
+// # result
+//
+//	string   // a string representation of the variables in the form:
+//
+//		[NAME1="VALUE1",NAME2="VALUE2",NAME3="VALUE3"]
+//
+// If the map is empty the result is "[]".
+func (v Vars) String() string {
+	n := v.Names()
+	ls := make([]string, 0, len(n))
+	for _, k := range n {
+		ls = append(ls, k+`="`+v[k]+`"`)
+	}
+	return "[" + strings.Join(ls, ",") + "]"
+}
diff --git a/vars_test.go b/vars_test.go
new file mode 100644
index 0000000..5e682ae
--- /dev/null
+++ b/vars_test.go
@@ -0,0 +1,74 @@
+package env
+
+import (
+	"errors"
+	"os"
+	"testing"
+
+	"github.com/blugnu/test"
+)
+
+func TestVars_Names(t *testing.T) {
+	// ACT
+	result := Vars{
+		"VAR3": "value2",
+		"VAR1": "value1",
+		"VAR2": "value2",
+	}.Names()
+
+	// ASSERT
+	test.That(t, result).Equals([]string{"VAR1", "VAR2", "VAR3"})
+}
+
+func TestVars_Set(t *testing.T) {
+	// ARRANGE
+	defer State().Reset()
+	os.Clearenv()
+
+	// ACT
+	err := Vars{
+		"VAR1": "value1",
+		"VAR2": "value2",
+	}.Set()
+
+	// ASSERT
+	test.That(t, err).IsNil()
+	test.That(t, os.Getenv("VAR1")).Equals("value1")
+	test.That(t, os.Getenv("VAR2")).Equals("value2")
+}
+
+func TestVars_Set_WhenSetenvFails(t *testing.T) {
+	// ARRANGE
+	defer State().Reset()
+
+	seterr := errors.New("setenv error")
+	defer test.Using(&osSetenv, func(string, string) error {
+		return seterr
+	})()
+
+	// ACT
+	err := Vars{"VAR1": "value1"}.Set()
+
+	// ASSERT
+	test.Error(t, err).Is(seterr)
+}
+
+func TestVars_String(t *testing.T) {
+	// ACT
+	result := Vars{
+		"VAR3": "value3",
+		"VAR1": "value1",
+		"VAR2": "value2",
+	}.String()
+
+	// ASSERT
+	test.That(t, result).Equals(`[VAR1="value1",VAR2="value2",VAR3="value3"]`)
+}
+
+func TestVars_String_WhenEmpty(t *testing.T) {
+	// ACT
+	result := Vars{}.String()
+
+	// ASSERT
+	test.That(t, result).Equals("[]")
+}