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#!/usr/bin/env ruby
require "curses"
# A curses based file viewer.
class FileViewer
# Create a new FileViewer and view the file.
def initialize(filename)
@data_lines = []
@screen = nil
@top = nil
init_curses
load_file(filename)
interact
end
# Perform the curses setup.
def init_curses
Curses.init_screen
Curses.nonl
Curses.cbreak
Curses.noecho
@screen = Curses.stdscr
@screen.scrollok(true)
#@screen.keypad(true)
end
# Load the file into memory and
# put the first part on the curses display.
def load_file(filename)
@data_lines = File.readlines(filename).map(&:chomp)
@top = 0
@data_lines[0..@screen.maxy-1].each_with_index do |line, idx|
@screen.setpos(idx, 0)
@screen.addstr(line)
end
@screen.setpos(0, 0)
@screen.refresh
rescue
raise "cannot open file '#{filename}' for reading"
end
# Scroll the display up by one line.
def scroll_up
if @top > 0
@screen.scrl(-1)
@top -= 1
str = @data_lines[@top]
if str
@screen.setpos(0, 0)
@screen.addstr(str)
end
return true
else
return false
end
end
# Scroll the display down by one line.
def scroll_down
if @top + @screen.maxy < @data_lines.length
@screen.scrl(1)
@top += 1
str = @data_lines[@top + @screen.maxy - 1]
if str
@screen.setpos(@screen.maxy - 1, 0)
@screen.addstr(str)
end
return true
else
return false
end
end
# Allow the user to interact with the display.
# This uses Emacs-like keybindings, and also
# vi-like keybindings as well, except that left
# and right move to the beginning and end of the
# file, respectively.
def interact
loop do
result = true
c = Curses.getch
case c
when Curses::KEY_DOWN, Curses::KEY_CTRL_N, "j"
result = scroll_down
when Curses::KEY_UP, Curses::KEY_CTRL_P, "k"
result = scroll_up
when Curses::KEY_NPAGE, " "
(@screen.maxy - 1).times do |i|
if !scroll_down && i == 0
result = false
break
end
end
when Curses::KEY_PPAGE
(@screen.maxy - 1).times do |i|
if !scroll_up && i == 0
result = false
break
end
end
when Curses::KEY_LEFT, Curses::KEY_CTRL_T, "h"
while scroll_up
end
when Curses::KEY_RIGHT, Curses::KEY_CTRL_B, "l"
while scroll_down
end
when "q"
break
else
@screen.setpos(0, 0)
@screen.addstr("[unknown key `#{Curses.keyname(c)}'=#{c}] ")
end
if !result
Curses.beep
end
@screen.setpos(0, 0)
end
Curses.close_screen
end
end
# If we are being run as a main program...
if __FILE__ == $0
unless ARGV.size == 1
puts "usage: #{$0} file"
exit
end
viewer = FileViewer.new(ARGV[0])
end
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