shell: detect tmux and send different escape codes

This allows to change the scheme from within tmux.

From the tmux CHANGES (1.5):

  * Support passing through escape sequences to the underlying terminal by
    using DCS with a "tmux;" prefix.

Source:
http://permalink.gmane.org/gmane.comp.terminal-emulators.tmux.user/1324

Ref: morhetz/gruvbox#4 (comment)

templates/shell/dark.sh.erb

@@ -28,36 +28,44 @@ color19="<%= split_by_slash(@base["02"]["hex"]) %>" # Base 02
 color20="<%= split_by_slash(@base["04"]["hex"]) %>" # Base 04
 color21="<%= split_by_slash(@base["06"]["hex"]) %>" # Base 06
 
-# 16 color space
-printf "\e]4;0;rgb:$color00\e\\"
-printf "\e]4;1;rgb:$color01\e\\"
-printf "\e]4;2;rgb:$color02\e\\"
-printf "\e]4;3;rgb:$color03\e\\"
-printf "\e]4;4;rgb:$color04\e\\"
-printf "\e]4;5;rgb:$color05\e\\"
-printf "\e]4;6;rgb:$color06\e\\"
-printf "\e]4;7;rgb:$color07\e\\"
-printf "\e]4;8;rgb:$color08\e\\"
-printf "\e]4;9;rgb:$color09\e\\"
-printf "\e]4;10;rgb:$color10\e\\"
-printf "\e]4;11;rgb:$color11\e\\"
-printf "\e]4;12;rgb:$color12\e\\"
-printf "\e]4;13;rgb:$color13\e\\"
-printf "\e]4;14;rgb:$color14\e\\"
-printf "\e]4;15;rgb:$color15\e\\"
+if [[ -n "$TMUX" ]]; then
+  # tell tmux to pass the escape sequences through
+  # (Source: http://permalink.gmane.org/gmane.comp.terminal-emulators.tmux.user/1324)
+  printf_template="\ePtmux;\e\e]4;%d;rgb:%s\a\e\\"
+else
+  printf_template="\e]4;%d;rgb:%s\e\\"
+fi
 
+# 16 color space
+printf $printf_template 0  $color00
+printf $printf_template 1  $color01
+printf $printf_template 2  $color02
+printf $printf_template 3  $color03
+printf $printf_template 4  $color04
+printf $printf_template 5  $color05
+printf $printf_template 6  $color06
+printf $printf_template 7  $color07
+printf $printf_template 8  $color08
+printf $printf_template 9  $color09
+printf $printf_template 10 $color10
+printf $printf_template 11 $color11
+printf $printf_template 12 $color12
+printf $printf_template 13 $color13
+printf $printf_template 14 $color14
+printf $printf_template 15 $color15
 
 # 256 color space
 if [ "$TERM" != linux ]; then
-  printf "\e]4;16;rgb:$color16\e\\"
-  printf "\e]4;17;rgb:$color17\e\\"
-  printf "\e]4;18;rgb:$color18\e\\"
-  printf "\e]4;19;rgb:$color19\e\\"
-  printf "\e]4;20;rgb:$color20\e\\"
-  printf "\e]4;21;rgb:$color21\e\\"
+  printf $printf_template 16 $color16
+  printf $printf_template 17 $color17
+  printf $printf_template 18 $color18
+  printf $printf_template 19 $color19
+  printf $printf_template 20 $color20
+  printf $printf_template 21 $color21
 fi
 
 # clean up
+unset printf_template
 unset color00
 unset color01
 unset color02
@@ -79,4 +87,4 @@ unset color17
 unset color18
 unset color19
 unset color20
-unset color21
+unset color21