Extend Sprintf to allow formatting a slice

README.md

@@ -14,4 +14,15 @@ fmt.Println(remoteCmd)
 // Output: ssh ubuntu@foo.com 'find . -iname '\''*.go'\'' | wc -l'
 ```
 
+Also slightly extends `Sprintf` syntax to allow easily passing in slices. This
+is a common use case when interacting with commands that take in a list of
+arguments:
+
+```go
+// Support for passing in a slice of arguments
+gitcmd := shell.Sprintf("git add %S", []string{"foo.go", "bar.go", "test data"})
+fmt.Println(gitcmd)
+// Output: git add foo.go bar.go 'test data'
+```
+
 See https://godoc.org/github.com/keegancsmith/shell for more information.

command.go

@@ -4,6 +4,9 @@ import (
 	"fmt"
 	"io"
 	"os/exec"
+	"reflect"
+	"strings"
+	"unicode"
 )
 
 // Commandf runs a shell command based on the format string
@@ -38,6 +41,20 @@ func (e escapable) Format(f fmt.State, c rune) {
 	if p, ok := f.Precision(); ok {
 		s += fmt.Sprintf(".%d", p)
 	}
+	// If we have an uppercase format char and a slice, format each slice
+	// element
+	if unicode.IsUpper(c) && reflect.TypeOf(e.x).Kind() == reflect.Slice {
+		s += strings.ToLower(string(c))
+		v := reflect.ValueOf(e.x)
+		for i := 0; i < v.Len(); i++ {
+			formatted := fmt.Sprintf(s, v.Index(i))
+			io.WriteString(f, ReadableEscapeArg(formatted))
+			if i+1 != v.Len() {
+				io.WriteString(f, " ")
+			}
+		}
+		return
+	}
 	s += string(c)
 	formatted := fmt.Sprintf(s, e.x)
 	io.WriteString(f, ReadableEscapeArg(formatted))

example_test.go

@@ -18,6 +18,13 @@ func ExampleSprintf() {
 	// Output: ssh ubuntu@foo.com 'find . -iname '\''*.go'\'' | wc -l'
 }
 
+func ExampleSprintf_StringSlice() {
+	// Support for passing in a slice of arguments
+	gitcmd := shell.Sprintf("git add %S", []string{"foo.go", "bar.go", "test data"})
+	fmt.Println(gitcmd)
+	// Output: git add foo.go bar.go 'test data'
+}
+
 func ExampleCommandf() {
 	out, err := shell.Commandf("echo %s", "hello world").Output()
 	if err != nil {