Document BUILDAH_* environment variables in buildah bud --help output

We also want to show the default settings.

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

Closes: #956
Approved by: rhatdan

cmd/buildah/bud.go

@@ -72,16 +72,9 @@ func budCmd(c *cli.Context) error {
 	}
 
 	dockerfiles := getDockerfiles(c.StringSlice("file"))
-	format := defaultFormat()
-	if c.IsSet("format") {
-		format = strings.ToLower(c.String("format"))
-	}
-	if strings.HasPrefix(format, "oci") {
-		format = imagebuildah.OCIv1ImageFormat
-	} else if strings.HasPrefix(format, "docker") {
-		format = imagebuildah.Dockerv2ImageFormat
-	} else {
-		return errors.Errorf("unrecognized image type %q", format)
+	format, err := getFormat(c)
+	if err != nil {
+		return err
 	}
 	layers := buildahcli.UseLayers()
 	if c.IsSet("layers") {

cmd/buildah/commit.go

@@ -3,7 +3,6 @@ package main
 import (
 	"fmt"
 	"os"
-	"strings"
 	"time"
 
 	"github.com/containers/image/storage"
@@ -116,13 +115,9 @@ func commitCmd(c *cli.Context) error {
 		timestamp = finfo.ModTime().UTC()
 	}
 
-	format := c.String("format")
-	if strings.HasPrefix(strings.ToLower(format), "oci") {
-		format = buildah.OCIv1ImageManifest
-	} else if strings.HasPrefix(strings.ToLower(format), "docker") {
-		format = buildah.Dockerv2ImageManifest
-	} else {
-		return errors.Errorf("unrecognized image type %q", format)
+	format, err := getFormat(c)
+	if err != nil {
+		return err
 	}
 	store, err := getStore(c)
 	if err != nil {

cmd/buildah/common.go

@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"os"
+	"strings"
 	"time"
 
 	is "github.com/containers/image/storage"
@@ -152,7 +153,7 @@ func defaultFormat() string {
 	if format != "" {
 		return format
 	}
-	return "oci"
+	return buildah.OCI
 }
 
 // imageIsParent goes through the layers in the store and checks if i.TopLayer is
@@ -216,3 +217,15 @@ func getImageOfTopLayer(images []storage.Image, layer string) []string {
 	}
 	return matches
 }
+
+func getFormat(c *cli.Context) (string, error) {
+	format := strings.ToLower(c.String("format"))
+	if strings.HasPrefix(format, buildah.OCI) {
+		return buildah.OCIv1ImageManifest, nil
+	}
+
+	if strings.HasPrefix(format, buildah.DOCKER) {
+		return buildah.Dockerv2ImageManifest, nil
+	}
+	return "", errors.Errorf("unrecognized image type %q", format)
+}

common.go

@@ -7,6 +7,13 @@ import (
 	"github.com/containers/image/types"
 )
 
+const (
+	// OCI used to define the "oci" image format
+	OCI = "oci"
+	// DOCKER used to define the "docker" image format
+	DOCKER = "docker"
+)
+
 func getCopyOptions(reportWriter io.Writer, sourceSystemContext *types.SystemContext, destinationSystemContext *types.SystemContext, manifestType string) *cp.Options {
 	return &cp.Options{
 		ReportWriter:          reportWriter,

pkg/cli/common.go

@@ -10,12 +10,12 @@ import (
 	"strings"
 
 	"github.com/opencontainers/runtime-spec/specs-go"
+	"github.com/projectatomic/buildah"
 	"github.com/projectatomic/buildah/util"
 	"github.com/urfave/cli"
 )
 
 var (
-	runtime     = util.Runtime()
 	usernsFlags = []cli.Flag{
 		cli.StringFlag{
 			Name:  "userns",
@@ -113,7 +113,8 @@ var (
 		},
 		cli.StringFlag{
 			Name:  "format",
-			Usage: "`format` of the built image's manifest and metadata",
+			Usage: "`format` of the built image's manifest and metadata. Use BUILDAH_FORMAT environment variable to override.",
+			Value: DefaultFormat(),
 		},
 		cli.StringFlag{
 			Name:  "iidfile",
@@ -121,7 +122,8 @@ var (
 		},
 		cli.StringFlag{
 			Name:  "isolation",
-			Usage: "`type` of process isolation to use",
+			Usage: "`type` of process isolation to use. Use BUILDAH_ISOLATION environment variable to override.",
+			Value: DefaultIsolation(),
 		},
 		cli.StringSliceFlag{
 			Name:  "label",
@@ -129,7 +131,7 @@ var (
 		},
 		cli.BoolFlag{
 			Name:  "layers",
-			Usage: fmt.Sprintf("cache intermediate layers during build (default %t)", UseLayers()),
+			Usage: fmt.Sprintf("cache intermediate layers during build. Use BUILDAH_LAYERS environment variable to override. (default %t)", UseLayers()),
 		},
 		cli.BoolFlag{
 			Name:  "no-cache",
@@ -161,8 +163,8 @@ var (
 		},
 		cli.StringFlag{
 			Name:  "runtime",
-			Usage: "`path` to an alternate runtime",
-			Value: runtime,
+			Usage: "`path` to an alternate runtime. Use BUILDAH_RUNTIME environment variable to override.",
+			Value: util.Runtime(),
 		},
 		cli.StringSliceFlag{
 			Name:  "runtime-flag",
@@ -260,3 +262,21 @@ func UseLayers() bool {
 	}
 	return false
 }
+
+// DefaultFormat returns the default image format
+func DefaultFormat() string {
+	format := os.Getenv("BUILDAH_FORMAT")
+	if format != "" {
+		return format
+	}
+	return buildah.OCI
+}
+
+// DefaultIsolation returns the default image format
+func DefaultIsolation() string {
+	isolation := os.Getenv("BUILDAH_ISOLATION")
+	if isolation != "" {
+		return isolation
+	}
+	return buildah.OCI
+}