diff --git a/adapter/handlebars/handlebars.go b/adapter/handlebars/handlebars.go
index e416faa..1068f5b 100644
--- a/adapter/handlebars/handlebars.go
+++ b/adapter/handlebars/handlebars.go
@@ -14,6 +14,7 @@ import (
 func Init(lang string, logger util.Logger, date date.Provider) {
 	helpers.RegisterSlug(logger, lang)
 	helpers.RegisterDate(logger, date)
+	helpers.RegisterShell(logger)
 }
 
 // HandlebarsRenderer holds parsed handlebars template and renders them.
diff --git a/adapter/handlebars/handlebars_test.go b/adapter/handlebars/handlebars_test.go
index 7c9a848..aedcd24 100644
--- a/adapter/handlebars/handlebars_test.go
+++ b/adapter/handlebars/handlebars_test.go
@@ -2,20 +2,18 @@ package handlebars
 
 import (
 	"fmt"
-	"log"
-	"os"
 	"testing"
 	"time"
 
+	"github.com/mickael-menu/zk/util"
 	"github.com/mickael-menu/zk/util/assert"
 	"github.com/mickael-menu/zk/util/date"
 	"github.com/mickael-menu/zk/util/fixtures"
 )
 
 func init() {
-	logger := log.New(os.Stderr, "zk: warning: ", 0)
 	date := date.NewFrozen(time.Date(2009, 11, 17, 20, 34, 58, 651387237, time.UTC))
-	Init("en", logger, &date)
+	Init("en", &util.NullLogger, &date)
 }
 
 func TestRenderString(t *testing.T) {
@@ -82,3 +80,15 @@ func TestDateHelper(t *testing.T) {
 	test("timestamp-unix", "1258490098")
 	test("cust: %Y-%m", "cust: 2009-11")
 }
+
+func TestShellHelper(t *testing.T) {
+	sut := NewRenderer()
+	// block is passed as piped input
+	res, err := sut.Render(`{{#sh "tr '[a-z]' '[A-Z]'"}}Hello, world!{{/sh}}`, nil)
+	assert.Nil(t, err)
+	assert.Equal(t, res, "HELLO, WORLD!")
+	// inline
+	res, err = sut.Render(`{{sh "echo 'Hello, world!'"}}`, nil)
+	assert.Nil(t, err)
+	assert.Equal(t, res, "Hello, world!\n")
+}
diff --git a/adapter/handlebars/helpers/date.go b/adapter/handlebars/helpers/date.go
index 1d1eb56..c6e81a5 100644
--- a/adapter/handlebars/helpers/date.go
+++ b/adapter/handlebars/helpers/date.go
@@ -7,6 +7,14 @@ import (
 	"github.com/mickael-menu/zk/util/date"
 )
 
+// RegisterDate registers the {{date}} template helpers which format a given date.
+//
+// It supports various styles: short, medium, long, full, year, time,
+// timestamp, timestamp-unix or a custom strftime format.
+//
+// {{date}} -> 2009-11-17
+// {{date "medium"}} -> Nov 17, 2009
+// {{date "%Y-%m"}} -> 2009-11
 func RegisterDate(logger util.Logger, date date.Provider) {
 	raymond.RegisterHelper("date", func(arg string) string {
 		format := findFormat(arg)
diff --git a/adapter/handlebars/helpers/shell.go b/adapter/handlebars/helpers/shell.go
new file mode 100644
index 0000000..2bd0b69
--- /dev/null
+++ b/adapter/handlebars/helpers/shell.go
@@ -0,0 +1,40 @@
+package helpers
+
+import (
+	"os/exec"
+	"strings"
+
+	"github.com/aymerick/raymond"
+	"github.com/kballard/go-shellquote"
+	"github.com/mickael-menu/zk/util"
+)
+
+// RegisterShell registers the {{sh}} template helper, which runs shell commands.
+//
+// {{#sh "tr '[a-z]' '[A-Z]'"}}Hello, world!{{/sh}} -> HELLO, WORLD!
+// {{sh "echo 'Hello, world!'"}} -> Hello, world!
+func RegisterShell(logger util.Logger) {
+	raymond.RegisterHelper("sh", func(arg string, options *raymond.Options) string {
+		args, err := shellquote.Split(arg)
+		if err != nil {
+			logger.Printf("{{sh}} failed to parse command: %v: %v", arg, err)
+			return ""
+		}
+		if len(args) == 0 {
+			logger.Printf("{{sh}} expects a valid shell command, received: %v", arg)
+			return ""
+		}
+
+		cmd := exec.Command(args[0], args[1:]...)
+		// Feed any block content as piped input
+		cmd.Stdin = strings.NewReader(options.Fn())
+
+		output, err := cmd.Output()
+		if err != nil {
+			logger.Printf("{{sh}} command failed: %v", err)
+			return ""
+		}
+
+		return string(output)
+	})
+}
diff --git a/adapter/handlebars/helpers/slug.go b/adapter/handlebars/helpers/slug.go
index 9a1ee89..4d68ece 100644
--- a/adapter/handlebars/helpers/slug.go
+++ b/adapter/handlebars/helpers/slug.go
@@ -6,6 +6,10 @@ import (
 	"github.com/mickael-menu/zk/util"
 )
 
+// RegisterSlug registers a {{slug}} template helper to slugify text.
+//
+// {{slug "This will be slugified!"}} -> this-will-be-slugified
+// {{#slug}}This will be slugified!{{/slug}} -> this-will-be-slugified
 func RegisterSlug(logger util.Logger, lang string) {
 	raymond.RegisterHelper("slug", func(opt interface{}) string {
 		switch arg := opt.(type) {
diff --git a/go.mod b/go.mod
index aac88d7..bf50181 100644
--- a/go.mod
+++ b/go.mod
@@ -8,6 +8,7 @@ require (
 	github.com/google/go-cmp v0.3.1
 	github.com/gosimple/slug v1.9.0
 	github.com/hashicorp/hcl/v2 v2.8.1
+	github.com/kballard/go-shellquote v0.0.0-20180428030007-95032a82bc51
 	github.com/lestrrat-go/strftime v1.0.3
 	gopkg.in/yaml.v2 v2.4.0 // indirect
 )
diff --git a/go.sum b/go.sum
index 78f23d8..a64d0f9 100644
--- a/go.sum
+++ b/go.sum
@@ -21,6 +21,8 @@ github.com/gosimple/slug v1.9.0 h1:r5vDcYrFz9BmfIAMC829un9hq7hKM4cHUrsv36LbEqs=
 github.com/gosimple/slug v1.9.0/go.mod h1:AMZ+sOVe65uByN3kgEyf9WEBKBCSS+dJjMX9x4vDJbg=
 github.com/hashicorp/hcl/v2 v2.8.1 h1:FJ60CIYaMyJOKzPndhMyjiz353Fd+2jr6PodF5Xzb08=
 github.com/hashicorp/hcl/v2 v2.8.1/go.mod h1:bQTN5mpo+jewjJgh8jr0JUguIi7qPHUF6yIfAEN3jqY=
+github.com/kballard/go-shellquote v0.0.0-20180428030007-95032a82bc51 h1:Z9n2FFNUXsshfwJMBgNA0RU6/i7WVaAegv3PtuIHPMs=
+github.com/kballard/go-shellquote v0.0.0-20180428030007-95032a82bc51/go.mod h1:CzGEWj7cYgsdH8dAjBGEr58BoE7ScuLd+fwFZ44+/x8=
 github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
diff --git a/main.go b/main.go
index ca297ce..54cde9f 100644
--- a/main.go
+++ b/main.go
@@ -1,8 +1,13 @@
 package main
 
 import (
+	"log"
+	"os"
+
 	"github.com/alecthomas/kong"
+	"github.com/mickael-menu/zk/adapter/handlebars"
 	"github.com/mickael-menu/zk/cmd"
+	"github.com/mickael-menu/zk/util/date"
 )
 
 var cli struct {
@@ -11,6 +16,13 @@ var cli struct {
 }
 
 func main() {
+	logger := log.New(os.Stderr, "zk: warning: ", 0)
+	// zk is short-lived, so we freeze the current date to use the same date
+	// for any rendering during the execution.
+	date := date.NewFrozenNow()
+	// FIXME take the language from the config
+	handlebars.Init("en", logger, &date)
+
 	ctx := kong.Parse(&cli,
 		kong.Name("zk"),
 	)
diff --git a/util/logger.go b/util/logger.go
index d8f626d..3a6cdba 100644
--- a/util/logger.go
+++ b/util/logger.go
@@ -6,3 +6,12 @@ type Logger interface {
 	Printf(format string, v ...interface{})
 	Println(v ...interface{})
 }
+
+// NullLogger is a logger ignoring any input.
+var NullLogger = nullLogger{}
+
+type nullLogger struct{}
+
+func (n *nullLogger) Printf(format string, v ...interface{}) {}
+
+func (n *nullLogger) Println(v ...interface{}) {}