feat: tail function for templates

internal/template.go

@@ -3,13 +3,15 @@ package internal
 import (
 	"bytes"
 	"fmt"
+	"math"
 	"strings"
 	"text/template"
 )
 
 var UtilFns = template.FuncMap{
 	"cut":     cut,
 	"head":    head,
+	"tail":    tail,
 	"iter":    iterItems,
 	"iterMap": iterMap,
 	"revCut":  reverseCut,
@@ -47,6 +49,21 @@ func head(i int, s string) (string, error) {
 	return splitBy("\n", i, s)
 }
 
+func tail(i int, s string) (string, error) {
+	if i < 0 {
+		headIdx := math.Abs(float64(i))
+		return head(int(headIdx)-1, s)
+	}
+	lines := strings.Split(s, "\n")
+	numLines := len(lines)
+	if i > numLines-1 {
+		return "", fmt.Errorf("invalid tail index %d for %s", i, s)
+	}
+
+	fwdIdx := numLines - 1 - i
+	return lines[fwdIdx], nil
+}
+
 func iterItems(items ...string) []string {
 	return items
 }

internal/template_test.go

@@ -125,6 +125,35 @@ baz`,
 			},
 			want: "v123",
 		},
+		{
+			name: "Simple tail",
+			args: args{
+				proc: "tail 0",
+				input: `foo
+bar
+baz`,
+			},
+			want: "baz",
+		},
+		{
+			name: "Negative tail",
+			args: args{
+				proc: "tail -1",
+				input: `foo
+bar
+baz`,
+			},
+			want: "foo",
+		},
+		{
+			name: "Tail error",
+			args: args{
+				proc: "tail 3",
+				input: `bar
+baz`,
+			},
+			wantErr: true,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

main.go

@@ -13,7 +13,7 @@ import (
 )
 
 const (
-	version = "0.35.2"
+	version = "0.36.0"
 )
 
 type args struct {