[feat] ExecForEach: Get parameters by column index

README.md

@@ -172,7 +172,9 @@ In the `ping` example, we knew the exact arguments we wanted to send the command
 We might like to be able to run the external command repeatedly, each time passing it the next line of data from the pipe as an argument. No worries:
 
 ```go
-script.Args().ExecForEach("ping -c 1 {{.}}").Stdout()
+// {{.Raw}} is original input
+// {{index .Cols N}} N indicates which column; 
+script.Args().ExecForEach("ping -c 1 {{.Raw}}").Stdout()
 ```
 
 That `{{.}}` is standard Go template syntax; it'll substitute each line of data from the pipe into the command line before it's executed. You can write as fancy a Go template expression as you want here (but this simple example probably covers most use cases).

script.go

@@ -399,6 +399,12 @@ func (p *Pipe) Exec(cmdLine string) *Pipe {
 	})
 }
 
+// inputFields for Go template
+type inputFields struct {
+	Raw  string   // original input
+	Cols []string // columns of line
+}
+
 // ExecForEach renders cmdLine as a Go template for each line of input, running
 // the resulting command, and produces the combined output of all these
 // commands in sequence. See [Pipe.Exec] for error handling details.
@@ -416,7 +422,12 @@ func (p *Pipe) ExecForEach(cmdLine string) *Pipe {
 		scanner := bufio.NewScanner(r)
 		for scanner.Scan() {
 			cmdLine := strings.Builder{}
-			err := tpl.Execute(&cmdLine, scanner.Text())
+			line := scanner.Text()
+			fields := strings.Fields(line)
+			err := tpl.Execute(&cmdLine, inputFields{
+				Raw:  line,
+				Cols: fields,
+			})
 			if err != nil {
 				return err
 			}

script_unix_test.go

@@ -52,7 +52,7 @@ func TestExecErrorsRunningShellCommandWithUnterminatedStringArgument(t *testing.
 
 func TestExecForEach_RunsEchoWithABCAndGetsOutputABC(t *testing.T) {
 	t.Parallel()
-	p := script.Echo("a\nb\nc\n").ExecForEach("echo {{.}}")
+	p := script.Echo("a\nb\nc\n").ExecForEach("echo {{.Raw}}")
 	if p.Error() != nil {
 		t.Fatal(p.Error())
 	}
@@ -82,6 +82,22 @@ func TestExecForEach_CorrectlyEvaluatesTemplateContainingIfStatement(t *testing.
 	}
 }
 
+func TestExecForEach_GetColunmsByIndex(t *testing.T) {
+	t.Parallel()
+	p := script.Echo("a b c d e\naa bb cc dd ee").ExecForEach("echo {{index .Cols 1}} {{index .Cols 4}}; ")
+	if p.Error() != nil {
+		t.Fatal(p.Error())
+	}
+	want := "b e;\nbb ee;\n"
+	got, err := p.String()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if want != got {
+		t.Error(cmp.Diff(want, got))
+	}
+}
+
 func TestExecPipesDataToExternalCommandAndGetsExpectedOutput(t *testing.T) {
 	t.Parallel()
 	p := script.File("testdata/hello.txt").Exec("cat")
@@ -182,9 +198,13 @@ func ExamplePipe_Exec() {
 }
 
 func ExamplePipe_ExecForEach() {
-	script.Echo("a\nb\nc\n").ExecForEach("echo {{.}}").Stdout()
+	script.Echo("a\nb\nc\n").ExecForEach("echo {{.Raw}}").Stdout()
+	script.Echo("a aa\nb bb\nc cc\n").ExecForEach("echo {{index .Cols 1}} {{index .Cols 0}}").Stdout()
 	// Output:
 	// a
 	// b
 	// c
+	// aa a
+	// bb b
+	// cc c
 }