[SOLVED] calling sleep from an awk script

scottfial · 2010-06-22 07:21:29

I am working on an awk script which repeatedly does some work and then sleeps. Most of the time it is sleeping and while it is sleeping I would like to be able to hit control-c to abort the program. Example awk scripts I have seen suggest this should be possible by testing for a non-zero exit code from the sleep call. However, it doesn't work and my program won't let me stop it. The following test program prints "0" whether I abort the sleep with control-c or wait for it to terminate normally:

#!/bin/awk -f

BEGIN {
  print system("sleep 10")
}

My arch system is up to date. From the "info" man page for sleep it says an abnormal termination should yield a non-zero exit code. I've tried calling other programs instead of sleep and they return non-zero exit codes when I hit control-c on them. I've tried invoking as "/bin/sleep 10" and "env sleep 10" as well. Nothing works. Any idea what I'm doing wrong?

Last edited by scottfial (2010-07-09 08:05:35)

ber_t · 2010-06-22 08:05:45

I don't know, why your awk script does not work as expected, but the following works for me:

#!/bin/awk -f

BEGIN {
  print system("trap 'exit 1' 2; sleep 10")
}

Last edited by ber_t (2010-06-22 08:06:03)

scottfial · 2010-06-22 08:39:03

Your suggestion works ber_t (you knew that). Thanks! But I'm the kind of guy who still needs to know why his perfectly reasonable code didn't work. Specifically, why won't this loop terminate when I hit control-c:

#!/bin/awk -f
do {
  # do stuff...
} while (!system("sleep 10"))

Its driving me crazy. The same basic approach works fine in lua:

#!/usr/bin/lua
repeat
  -- do stuff
until os.execute("sleep 10") ~= 0

What the flip?

ber_t · 2010-06-22 09:18:25

Well, after trying both, lua and awk, I made the observation, that lua executes the sleep directly, whereas awk uses a shell to run the system command:

$ ./test.lua &
$ ps axo pid,ppid,command
  PID  PPID COMMAND
 2083  2081 bash
 2434  2083 /usr/bin/lua ./test.lua
 2435  2434 sleep 10
$ ./test.awk &
$ ps axo pid,ppid,command
  PID  PPID COMMAND
 2083  2081 bash
 2451  2083 /bin/awk -f ./test.awk
 2452  2451 sh -c trap 'exit 1' 2; sleep 10
 2453  2452 sleep 10

By default, the shell returns a zero exit status when hitting Ctrl-C. Using "trap 'exit 1' 2" tells her to exit appropriately.

scottfial · 2010-06-22 09:32:48

I think the shell you're seeing might be getting created because of the "trap;sleep" combo. When I run your ps command against my test program using just "sleep 10" I don't see an invocation of "sh". It looks just like the lua version.

ber_t · 2010-06-22 09:37:11

scottfial wrote:

I think the shell you're seeing might be getting created because of the "trap;sleep" combo. When I run your ps command against my test program using just "sleep 10" I don't see an invocation of "sh". It looks just like the lua version.

You're absolutely correct. So we're both clueless and have to wait for others to join this thread.

skanky · 2010-06-22 10:06:37

Not sure I've got a complete handle on this, but this might be a useful pointer:

997 ~ $env sleep 10 || echo true
^C
997 ~ $env sleep 10 || echo true
^Z
[2]+  Stopped                 env sleep 10
true
997 ~ $env sleep 10 || echo true
^\Quit
true

It seems that SIGINT doesn't cause sleep to "fail", whereas SIGQUIT and SIGTSTP do. So (and I haven't tried wrapping this yet) it might be worth trying to quit the script with SIGQUIT or SIGTSTP + kill.

(edit clarification)

Last edited by skanky (2010-06-22 10:14:36)

scottfial · 2010-06-22 17:11:26

Sleep must return something useful when you it ^C because the following lua program:

#!/usr/bin/lua

local exit_code

repeat
  exit_code = os.execute("sleep 10")
  print("exit_code: " .. exit_code)
until exit_code ~= 0

produces the following output if I let the sleep expire twice and then hit ^C:

exit_code: 0
exit_code: 0
^Cexit_code: 2

and then it terminates. Now here's an equivalent awk program:

#!/bin/awk -f

BEGIN {
  do {
    exit_code = system("sleep 10")
    print "exit_code: " exit_code
  } while (!exit_code)

It produces the following if I let the sleep expire twice and then hit ^C twice:

exit_code: 0
exit_code: 0
^Cexit_code: 0
^Cexit_code: 0

and it never terminates. I have to kill it. Just to make sure that awk is seeing exit codes, I compiled this C program

int main(int argc, char *argv[]) {
  return 2;
}

and changed my awk program to call "a.out" rather than "sleep 10". The result is

exit_code: 2

and then it terminates.

I got the following on the command line:

$ ./a.out
$ echo $?
2
$ sleep 10
^C
$ echo $?
130

Excuse me? 130? Lua saw a 2. None of this makes sense. Its as if awk has singled out "sleep" to not work! Where am I going wrong?

Last edited by scottfial (2010-06-22 17:18:54)

awkwood · 2010-06-22 18:56:42

Ber_t is correct, the shell does return an exit code of 0 for Ctrl+C.
Here's a dodgy workaround to get your awk script running as intended

#!/bin/awk -f

BEGIN {
  do {
    exit_code = system("sleep 10 && exit 27")
    print "exit_code: " exit_code
  } while (exit_code != 0)
}

Arch Linux

#1 2010-06-22 07:21:29

[SOLVED] calling sleep from an awk script

#2 2010-06-22 08:05:45

Re: [SOLVED] calling sleep from an awk script

#3 2010-06-22 08:39:03

Re: [SOLVED] calling sleep from an awk script

#4 2010-06-22 09:18:25

Re: [SOLVED] calling sleep from an awk script

#5 2010-06-22 09:32:48

Re: [SOLVED] calling sleep from an awk script

#6 2010-06-22 09:37:11

Re: [SOLVED] calling sleep from an awk script

#7 2010-06-22 10:06:37

Re: [SOLVED] calling sleep from an awk script

#8 2010-06-22 17:11:26

Re: [SOLVED] calling sleep from an awk script

#9 2010-06-22 18:56:42

Re: [SOLVED] calling sleep from an awk script

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