Honor RESTIC_CACHE_DIR environment variable

Fix #3382: restic check doesn't obey the RESTIC_CACHE_DIR environment variable

cmd/restic/cmd_check.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/spf13/cobra"
 
+	"github.com/restic/restic/internal/cache"
 	"github.com/restic/restic/internal/checker"
 	"github.com/restic/restic/internal/errors"
 	"github.com/restic/restic/internal/fs"
@@ -146,6 +147,9 @@ func prepareCheckCache(opts CheckOptions, gopts *GlobalOptions) (cleanup func())
 	}
 
 	cachedir := gopts.CacheDir
+	if cachedir == "" {
+		cachedir = cache.EnvDir()
+	}
 
 	// use a cache in a temporary directory
 	tempdir, err := ioutil.TempDir(cachedir, "restic-check-cache-")

internal/cache/dir.go

@@ -6,10 +6,15 @@ import (
 	"path/filepath"
 )
 
+// EnvDir return $RESTIC_CACHE_DIR env
+func EnvDir() string {
+	return os.Getenv("RESTIC_CACHE_DIR")
+}
+
 // DefaultDir returns $RESTIC_CACHE_DIR, or the default cache directory
 // for the current OS if that variable is not set.
 func DefaultDir() (cachedir string, err error) {
-	cachedir = os.Getenv("RESTIC_CACHE_DIR")
+	cachedir = EnvDir()
 	if cachedir != "" {
 		return cachedir, nil
 	}