About

A simple snake game written in Bash.

How to Play

Direction control: vim-style keys h, j, k and l; Quit: q Accept both upper- and lower-case.

Some Implementation Details

• Bash-snake has two processes, the foreground one responds to user's control commands, the background one draws the board. kill and trap are used to enable communication between the two processes.

  The foreground process getchar() ignores SIGINT and SIGQUIT, and replies to the signal of death SIG_HEAD by returning from the function getchar().

  The background process game_loop() traps direction control signals from the keyboard, and self-defined signal SIG_QUIT which indicates the press of Q button.

• Use $! to grasp the PID of the latest created background process.

• When setting up several traps, it's necessary to guarantee that the normal execution will not be interrupted by the signal handling if the handlers envolve modification of some variables it depends on.

• The snake is represented by the coordinate $head_r and $head_c indicating the row and column on which the snake head is, and a string $body which stores the directions from the head to tail. e.g. a snake with this shape (@ is the head):

   @
   oooo
      o
  

  will have a $body with value '21112', meaning 'down,right,right,right,down'.

  With the above scheme and the coordinates of the snake head, we can figure out the position the the entire snake body, without storing every part of its body.

• The board is represented by a "2D array", which is actually implemented by a bunch of bash arrays and the eval command. For example, assigning 123 to the array entry arr[5][6] is done with eval "arr$i[$j]=123".

• The board is re-drawn in each iteration, which happens every 0.03 seconds.

• Coloring is implemented with the escaped sequences of the terminal.