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Trapping signals in Ruby

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It’s pretty easy to handle signals in Ruby, which is sometimes necessary when you want your code to interact with the system running it.

Signalz Ahoy!

If you want to know which kill signals you have:

bash-3.2$ kill -l
1) SIGHUP       2) SIGINT       3) SIGQUIT      4) SIGILL
5) SIGTRAP      6) SIGABRT      7) SIGEMT       8) SIGFPE
9) SIGKILL     10) SIGBUS      11) SIGSEGV     12) SIGSYS
13) SIGPIPE     14) SIGALRM     15) SIGTERM     16) SIGURG
17) SIGSTOP     18) SIGTSTP     19) SIGCONT     20) SIGCHLD
21) SIGTTIN     22) SIGTTOU     23) SIGIO       24) SIGXCPU
25) SIGXFSZ     26) SIGVTALRM   27) SIGPROF     28) SIGWINCH
29) SIGINFO     30) SIGUSR1     31) SIGUSR2

If you want to know which kill signals Ruby recognises:

irb(main):002:0> Signal.list.keys.join ", "
=> "USR1, BUS, USR2, TERM, SEGV, KILL, EMT, EXIT, STOP, SYS, TRAP, INFO, IOT, HUP, INT, WINCH, XCPU, TTIN, CLD, TSTP, FPE, IO, TTOU, PROF, CHLD, CONT, PIPE, ABRT, VTALRM, QUIT, ILL, XFSZ, URG, ALRM"
irb(main):003:0>

Some quick-n-dirty source code:

There’s probably better ways of doing this, but here’s a stupid little example demonstrating how it could work:

bash-3.2$ cat signal.rb

$hups = 0

def quit_on_int
  puts "Quitting on interrupt signal."
  exit
end

def quit_on_quit
  puts "U sure killed me guud!"
  exit
end

def handle_hup
  $hups=$hups+1
  puts "HUP! (count: #{$hups})"
end

while true
  trap("INT") {quit_on_int}
  trap("HUP") {handle_hup}
  trap("QUIT") {quit_on_quit}
end

Example in use:

bash-3.2$ ruby signal.rb
HUP! (count: 1)
HUP! (count: 2)
HUP! (count: 3)
^CQuitting on interrupt signal.
bash-3.2$

We run the program as above, then send it three SIGHUPs (i.e., using "kill -HUP pid"). We break out the program using ^C (ctrl-c), sending an Interrupt. Note this may not work in windows.

bash-3.2$ ruby signal.rb
U sure killed me guud!
bash-3.2$

Here we run the program again, and send it a SIGQUIT ("kill -QUIT pid").

Written by art

December 7th, 2007 at 12:21 am

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