init commit

go.mod

@@ -0,0 +1,3 @@
+module github.com/nakatamixi/maskedenv
+
+go 1.14

main.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"strings"
+)
+
+var (
+	headSize = flag.Int("h", 0, "unmask head size")
+	tailSize = flag.Int("t", 0, "unmask tail size")
+)
+
+func main() {
+	flag.Parse()
+	for _, e := range os.Environ() {
+		pair := strings.SplitN(e, "=", 2)
+		fmt.Printf("%s=%s\n", pair[0], MaskedStr(pair[1], *headSize, *tailSize))
+	}
+}
+
+func MaskedStr(origin string, hs, ts int) string {
+	head := origin
+	tail := origin
+	if len(origin) >= hs {
+		head = origin[:hs]
+	}
+	if len(origin) >= ts {
+		tail = origin[len(origin)-ts:]
+	}
+	masked := ""
+	if len(origin)-hs-ts > 0 {
+		masked = strings.Repeat("*", len(origin)-hs-ts)
+	}
+	return fmt.Sprintf("%s%s%s", head, masked, tail)
+}

main_test.go

@@ -0,0 +1,59 @@
+package main
+
+import "testing"
+
+func TestMaskedStr(t *testing.T) {
+	testCases := []struct {
+		name     string
+		origin   string
+		hs, ts   int
+		expected string
+	}{
+		{
+			name:   "empty origin",
+			origin: "", hs: 0, ts: 0,
+			expected: "",
+		},
+		{
+			name:   "full masked",
+			origin: "ab", hs: 0, ts: 0,
+			expected: "**",
+		},
+		{
+			name:   "head size within length",
+			origin: "ab", hs: 1, ts: 0,
+			expected: "a*",
+		},
+		{
+			name:   "tail size within length",
+			origin: "ab", hs: 0, ts: 1,
+			expected: "*b",
+		},
+		{
+			name:   "head size equal length",
+			origin: "ab", hs: 2, ts: 0,
+			expected: "ab",
+		},
+		{
+			name:   "tail size equal length",
+			origin: "ab", hs: 0, ts: 2,
+			expected: "ab",
+		},
+		{
+			name:   "head size over length",
+			origin: "ab", hs: 3, ts: 0,
+			expected: "ab",
+		},
+		{
+			name:   "tail size over length",
+			origin: "ab", hs: 0, ts: 3,
+			expected: "ab",
+		},
+	}
+	for _, tc := range testCases {
+		actual := MaskedStr(tc.origin, tc.hs, tc.ts)
+		if actual != tc.expected {
+			t.Errorf("MaskedStr failed. case: %s, actual: %s", tc.name, actual)
+		}
+	}
+}