# -*- ruby -*-

# hello world
# print a simple string on stdout
puts "Hello World"

# argv
# access command line parameters (no segmentation fault accepted, nor silent exception, so some languages must explicitly check the presence of the argument)
puts ARGV[0]

# env
# access environment variable
puts ENV["HOME"]

# test file exists
# return exit code error (non zero) if a file does not exist
test ?e, "/etc/mtab" or exit 1

# test file readable
# return exit code error (non zero) if a file is not readable
test ?r, "/etc/mtab" or exit 1

# formatting
# print integers in a simple formatted string
a=1; b=2; puts "#{a} + #{b} = #{a + b}"

# system
# call an external program and check the return value
system "false" or $stderr.puts "false failed"; system "echo done"

# sed in place
# remove #-comments from a file (modifying the file, i.e. in place)
% ruby -pi -e '$_.sub!(/#.*/, "")'

# compile what must be
# find and compile .c files into .o when the .o is old or absent
Dir['**/*.c'].each{|c|
  o = c.sub('.c$', '.o')
  if test ?>, c, o then
    puts "compiling #{c} to #{o}"
    system("gcc", "-c", "-o", o, c)
  end
}


# grep
# grep with -F -i -h handling, usage, grep'ing many files
require 'getopts'
getopts('Fih')

ARGV.empty? || $OPT_h and 
  (puts "usage: grep [-F] [-i] regexp [files...]"; exit 1)

r = ARGV.shift
r = Regexp.quote(r) if $OPT_F
r = /#{r}/i if $OPT_i

prefix = ARGV.size > 1

while gets
  print prefix ? "#{ARGF}:" : '', $_ if $_ =~ /#{r}/
end