Question

When I ran the ruby code below, pressing ctrl + c would immediately stop the program

trap("INT") { exit }
while line = gets; puts line; end

However, when I use system() command before the gets, pressing ctrl + c would not take any effect unless I hit “Enter”. It seems like it has to do with system() forking a child process and somehow the parent could no longer detect SIGINT. How would you change the code so that ctrl + c would take immediate effect for the code below

trap("INT") { exit }

if system("which ruby > /dev/null")
  puts "ruby is installed"
end

while line = gets; puts line; end

Answer 1

That looks like a bug in the signal handling which was fixed in 1.9, to work around your problem, define the signal trap after the system call:

if system("which ruby > /dev/null")
  puts "ruby is installed"
end
trap("INT") { p 'Ciao!'; exit }
while line = gets; puts line; end

Not ideal, but it works.