Consistently use STDERR for output. (#647)

This is basically these commands:
```shell
sed -i '[email protected](@fmt.Fprintf(os.Stderr, @g' $(git grep fmt.Printf | cut -d':' -f 1 | uniq)
sed -i '[email protected](@fmt.Fprintln(os.Stderr, @g' $(git grep fmt.Println | cut -d':' -f 1 | uniq)
sed -i 's/os.Stdout/os.Stderr/g' $(git grep os.Stdout | cut -d':' -f 1)
```

Signed-off-by: Matt Moore <[email protected]>

Author: mattmoor

cmd/cosign/cli/attest.go

@@ -183,7 +183,7 @@ func AttestCmd(ctx context.Context, ko KeyOpts, imageRef string, certPath string
 	}
 
 	if !upload {
-		fmt.Println(base64.StdEncoding.EncodeToString(sig))
+		fmt.Fprintln(os.Stderr, base64.StdEncoding.EncodeToString(sig))
 		return nil
 	}
 

cmd/cosign/cli/clean.go

@@ -63,7 +63,7 @@ func CleanCmd(ctx context.Context, imageRef string) error {
 		return err
 	}
 	sigRef := cosign.AttachedImageTag(sigRepo, h, cosign.SignatureTagSuffix)
-	fmt.Println(sigRef)
+	fmt.Fprintln(os.Stderr, sigRef)
 
 	fmt.Fprintln(os.Stderr, "Deleting signature metadata...")
 

cmd/cosign/cli/download/sbom.go

@@ -43,7 +43,7 @@ func SBOM() *ffcli.Command {
 			if len(args) != 1 {
 				return flag.ErrHelp
 			}
-			_, err := SBOMCmd(ctx, args[0], os.Stdout)
+			_, err := SBOMCmd(ctx, args[0], os.Stderr)
 			return err
 		},
 	}

cmd/cosign/cli/download/signature.go

@@ -20,6 +20,7 @@ import (
 	"encoding/json"
 	"flag"
 	"fmt"
+	"os"
 
 	"github.com/google/go-containerregistry/pkg/name"
 	"github.com/peterbourgon/ff/v3/ffcli"
@@ -64,7 +65,7 @@ func SignatureCmd(ctx context.Context, imageRef string) error {
 		if err != nil {
 			return err
 		}
-		fmt.Println(string(b))
+		fmt.Fprintln(os.Stderr, string(b))
 	}
 	return nil
 }

cmd/cosign/cli/fulcio/fulcio.go

@@ -140,7 +140,7 @@ func getCertForOauthID(priv *ecdsa.PrivateKey, scp signingCertProvider, connecto
 	if err := VerifySCT(fr); err != nil {
 		return Resp{}, errors.Wrap(err, "verifying SCT")
 	}
-	fmt.Println("Successfully verified SCT...")
+	fmt.Fprintln(os.Stderr, "Successfully verified SCT...")
 	return fr, nil
 }
 

cmd/cosign/cli/generate.go

@@ -59,7 +59,7 @@ EXAMPLES
 			if len(args) != 1 {
 				return flag.ErrHelp
 			}
-			return GenerateCmd(ctx, args[0], annotations.annotations, os.Stdout)
+			return GenerateCmd(ctx, args[0], annotations.annotations, os.Stderr)
 		},
 	}
 }

cmd/cosign/cli/pivcli/commands.go

@@ -136,27 +136,27 @@ func (a *Attestations) Output() {
 		Type:  "CERTIFICATE",
 		Bytes: a.DeviceCert.Raw,
 	})
-	fmt.Println(string(b))
+	fmt.Fprintln(os.Stderr, string(b))
 
 	fmt.Fprintln(os.Stderr, "Printing key attestation certificate")
 	b = pem.EncodeToMemory(&pem.Block{
 		Type:  "CERTIFICATE",
 		Bytes: a.KeyCert.Raw,
 	})
-	fmt.Println(string(b))
+	fmt.Fprintln(os.Stderr, string(b))
 
 	fmt.Fprintln(os.Stderr, "Verifying certificates...")
 
 	fmt.Fprintln(os.Stderr, "Verified ok")
-	fmt.Println()
+	fmt.Fprintln(os.Stderr, )
 
 	fmt.Fprintln(os.Stderr, "Device info:")
-	fmt.Println("  Issuer:", a.DeviceCert.Issuer)
-	fmt.Println("  Form factor:", formFactorString(a.KeyAttestation.Formfactor))
-	fmt.Println("  PIN Policy:", pinPolicyStr(a.KeyAttestation.PINPolicy))
+	fmt.Fprintln(os.Stderr, "  Issuer:", a.DeviceCert.Issuer)
+	fmt.Fprintln(os.Stderr, "  Form factor:", formFactorString(a.KeyAttestation.Formfactor))
+	fmt.Fprintln(os.Stderr, "  PIN Policy:", pinPolicyStr(a.KeyAttestation.PINPolicy))
 
-	fmt.Printf("  Serial number: %d\n", a.KeyAttestation.Serial)
-	fmt.Printf("  Version: %d.%d.%d\n", a.KeyAttestation.Version.Major, a.KeyAttestation.Version.Minor, a.KeyAttestation.Version.Patch)
+	fmt.Fprintf(os.Stderr, "  Serial number: %d\n", a.KeyAttestation.Serial)
+	fmt.Fprintf(os.Stderr, "  Version: %d.%d.%d\n", a.KeyAttestation.Version.Major, a.KeyAttestation.Version.Minor, a.KeyAttestation.Version.Patch)
 }
 
 func AttestationCmd(_ context.Context, slotArg string) (*Attestations, error) {
@@ -261,7 +261,7 @@ func GenerateKeyCmd(ctx context.Context, managementKey string, randomKey bool, s
 		Bytes: b,
 	})
 
-	fmt.Println(string(pemBytes))
+	fmt.Fprintln(os.Stderr, string(pemBytes))
 	yk.Close()
 
 	att, err := AttestationCmd(ctx, slotArg)
@@ -305,7 +305,7 @@ var Confirm = func(p string) bool {
 
 	result, err := prompt.Run()
 	if err != nil {
-		fmt.Println(err)
+		fmt.Fprintln(os.Stderr, err)
 		return false
 	}
 	return strings.ToLower(result) == "y"

cmd/cosign/cli/pivcli/piv_tool.go

@@ -147,7 +147,7 @@ func Attestation() *ffcli.Command {
 				if err != nil {
 					return err
 				}
-				fmt.Println(string(b))
+				fmt.Fprintln(os.Stderr, string(b))
 			}
 			return err
 		},

cmd/cosign/cli/public_key.go

@@ -90,7 +90,7 @@ EXAMPLES
 				writer.Writer = f
 				defer f.Close()
 			} else {
-				writer.Writer = os.Stdout
+				writer.Writer = os.Stderr
 			}
 			pk := Pkopts{
 				KeyRef: *key,

cmd/cosign/cli/sign.go

@@ -339,7 +339,7 @@ func SignCmd(ctx context.Context, ko KeyOpts, annotations map[string]interface{}
 		}
 
 		if !upload {
-			fmt.Println(base64.StdEncoding.EncodeToString(sig))
+			fmt.Fprintln(os.Stderr, base64.StdEncoding.EncodeToString(sig))
 			continue
 		}