avoid duplicate calls to env methods

CHANGELOG.md

@@ -6,6 +6,7 @@ appear at the top.
 ## [Unreleased][]
 
   * Your contribution here!
+  * [#453](https://github.com/capistrano/sshkit/pull/453): fix and unify shell escaping for user/group/directory - [@grosser](https://github.com/grosser)
 
 ## [1.18.2][] (2019-02-03)
 

lib/sshkit/backends/abstract.rb

@@ -1,3 +1,5 @@
+require 'shellwords'
+
 module SSHKit
 
   module Backend
@@ -81,12 +83,12 @@ def execute(*args)
       def within(directory, &_block)
         (@pwd ||= []).push directory.to_s
         execute <<-EOTEST, verbosity: Logger::DEBUG
-          if test ! -d #{File.join(@pwd)}
-            then echo "Directory does not exist '#{File.join(@pwd)}'" 1>&2
+          if test ! -d #{File.join(@pwd).shellescape}
+            then echo "Directory does not exist '#{File.join(@pwd).shellescape}'" 1>&2
             false
           fi
-          EOTEST
-          yield
+        EOTEST
+        yield
       ensure
         @pwd.pop
       end
@@ -108,8 +110,8 @@ def as(who, &_block)
           @group = nil
         end
         execute <<-EOTEST, verbosity: Logger::DEBUG
-          if ! sudo -u #{@user} whoami > /dev/null
-            then echo "You cannot switch to user '#{@user}' using sudo, please check the sudoers file" 1>&2
+          if ! sudo -u #{@user.to_s.shellescape} whoami > /dev/null
+            then echo "You cannot switch to user '#{@user.to_s.shellescape}' using sudo, please check the sudoers file" 1>&2
             false
           fi
         EOTEST

lib/sshkit/command.rb

@@ -162,13 +162,15 @@ def environment_string
     end
 
     def with(&_block)
-      return yield unless environment_hash.any?
-      "( export #{environment_string} ; #{yield} )"
+      env_string = environment_string
+      return yield if env_string.empty?
+      "( export #{env_string} ; #{yield} )"
     end
 
     def user(&_block)
       return yield unless options[:user]
-      "sudo -u #{options[:user].to_s.shellescape} #{environment_string + " " unless environment_string.empty?}-- sh -c #{yield.shellescape}"
+      env_string = environment_string
+      "sudo -u #{options[:user].to_s.shellescape} #{env_string + " " unless env_string.empty?}-- sh -c #{yield.shellescape}"
     end
 
     def in_background(&_block)