From 6e6f07c58b948d6e43f3ccec90d55f96bc6e465d Mon Sep 17 00:00:00 2001
From: Harshavardhana <harsha@harshavardhana.net>
Date: Fri, 19 Dec 2014 03:32:13 -0800
Subject: [PATCH] Add simple ExecPipe() to be used with filesystem format work

---
 pkgs/utils/execpipe.go      | 46 +++++++++++++++++++++++++++++++++++++
 pkgs/utils/execpipe_test.go | 34 +++++++++++++++++++++++++++
 2 files changed, 80 insertions(+)
 create mode 100644 pkgs/utils/execpipe.go
 create mode 100644 pkgs/utils/execpipe_test.go

diff --git a/pkgs/utils/execpipe.go b/pkgs/utils/execpipe.go
new file mode 100644
index 000000000..4f1ba6b59
--- /dev/null
+++ b/pkgs/utils/execpipe.go
@@ -0,0 +1,46 @@
+package utils
+
+import (
+	"bytes"
+	"errors"
+	"os/exec"
+)
+
+// A simple ExecPipe() pipes exec.Cmd together - somewhat similar to how bash pipes "|" behave.
+// Each command's standard output is connected to the standard input of the next command
+// and the output of the final command is returned
+
+func ExecPipe(cmds ...*exec.Cmd) (pipeLineOutput []byte, pipeLineError error) {
+	// Require at least one command
+	if len(cmds) < 1 {
+		return nil, errors.New("Invalid argument")
+	}
+
+	// Collect the output from the command(s)
+	var output bytes.Buffer
+
+	lastIndex := len(cmds) - 1
+	for i, cmd := range cmds[:lastIndex] {
+		cmds[i+1].Stdin, _ = cmd.StdoutPipe()
+	}
+
+	// Final ---> output buffer
+	cmds[lastIndex].Stdout = &output
+
+	// Start each command
+	for _, cmd := range cmds {
+		if err := cmd.Start(); err != nil {
+			return output.Bytes(), err
+		}
+	}
+
+	// We should Wait() for each command to complete
+	for _, cmd := range cmds {
+		if err := cmd.Wait(); err != nil {
+			return output.Bytes(), err
+		}
+	}
+
+	// Return the output
+	return output.Bytes(), nil
+}
diff --git a/pkgs/utils/execpipe_test.go b/pkgs/utils/execpipe_test.go
new file mode 100644
index 000000000..f5fce2415
--- /dev/null
+++ b/pkgs/utils/execpipe_test.go
@@ -0,0 +1,34 @@
+// !build linux,amd64
+
+package utils
+
+import (
+	. "gopkg.in/check.v1"
+	"os/exec"
+	"testing"
+)
+
+type MySuite struct{}
+
+var _ = Suite(&MySuite{})
+
+func Test(t *testing.T) { TestingT(t) }
+
+func (s *MySuite) TestPiping(c *C) {
+	// Collect directories from the command-line
+	dirs := []string{"."}
+
+	// Run the command on each directory
+	for _, dir := range dirs {
+		// find $DIR -type f # Find all files
+		ls := exec.Command("ls", dir, "-l")
+
+		// | sort -t. -k2 # Sort by file extension
+		sort := exec.Command("sort", "-t.", "-k2")
+
+		// Run
+		output, err := ExecPipe(ls, sort)
+		c.Assert(err, IsNil)
+		c.Assert(len(output), Not(Equals), 0)
+	}
+}