Timeout a command in bash without unnecessary dela

Question

This answer to Command line command to auto-kill a command after a certain amount of time

proposes a 1-line method to timeout a long-running command from the bash command line:

( /path/to/slow command with options ) & sleep 5 ; kill $!

But it's possible that a given "long-running" command may finish earlier than the timeout. (Let's call it a "typically-long-running-but-sometimes-fast" command, or tlrbsf for fun.)

So this nifty 1-liner approach has a couple of problems. First, the sleep isn't conditional, so that sets an undesirable lower bound on the time taken for the sequence to finish. Consider 30s or 2m or even 5m for the sleep, when the tlrbsf command finishes in 2 seconds — highly undesirable. Second, the kill is unconditional, so this sequence will attempt to kill a non-running process and whine about it.

So...

Is there a way to timeout a typically-long-running-but-sometimes-fast ("tlrbsf") command that

• has a bash implementation (the other question already has Perl and C answers)
• will terminate at the earlier of the two: tlrbsf program termination, or timeout elapsed
• will not kill non-existing/non-running processes (or, optionally: will not complain about a bad kill)
• doesn't have to be a 1-liner
• can run under Cygwin or Linux

... and, for bonus points, runs the tlrbsf command in the foreground and any 'sleep' or extra process in the background, such that the stdin/stdout/stderr of the tlrbsf command can be redirected, same as if it had been run directly?

If so, please share your code. If not, please explain why.

I have spent awhile trying to hack the aforementioned example but I'm hitting the limit of my bash skills.

Answer 1

Kinda hacky, but it works. Doesn't work if you have other foreground processes (please help me fix this!)

sleep TIMEOUT & SPID=${!}; (YOUR COMMAND HERE; kill ${SPID}) & CPID=${!}; fg 1; kill ${CPID}

Actually, I think you can reverse it, meeting your 'bonus' criteria:

(YOUR COMMAND HERE & SPID=${!}; (sleep TIMEOUT; kill ${SPID}) & CPID=${!}; fg 1; kill ${CPID}) < asdf > fdsa

Answer 2

Here is a version that does not rely on spawning a child process - I needed a standalone script which embedded this functionality. It also does a fractional poll interval, so you can poll quicker. timeout would have been preferred - but I'm stuck on an old server

# wait_on_command <timeout> <poll interval> command
wait_on_command()
{
    local timeout=$1; shift
    local interval=$1; shift
    $* &
    local child=$!

    loops=$(bc <<< "($timeout * (1 / $interval)) + 0.5" | sed 's/\..*//g')
    ((t = loops))
    while ((t > 0)); do
        sleep $interval
        kill -0 $child &>/dev/null || return
        ((t -= 1))
    done

    kill $child &>/dev/null || kill -0 $child &>/dev/null || return
    sleep $interval
    kill -9 $child &>/dev/null
    echo Timed out
}

slow_command()
{
    sleep 2
    echo Completed normally
}

# wait 1 sec in 0.1 sec increments
wait_on_command 1 0.1 slow_command

# or call an external command
wait_on_command 1 0.1 sleep 10

Answer 3

OS X doesn't use bash 4 yet, nor does it have /usr/bin/timeout, so here's a function that works on OS X without home-brew or macports that is similar to /usr/bin/timeout (based on Tino's answer). Parameter validation, help, usage, and support for other signals are an exercise for reader.

# implement /usr/bin/timeout only if it doesn't exist
[ -n "$(type -p timeout 2>&1)" ] || function timeout { (
    set -m +b
    sleep "$1" &
    SPID=${!}
    ("${@:2}"; RETVAL=$?; kill ${SPID}; exit $RETVAL) &
    CPID=${!}
    wait %1
    SLEEPRETVAL=$?
    if [ $SLEEPRETVAL -eq 0 ] && kill ${CPID} >/dev/null 2>&1 ; then
      RETVAL=124
      # When you need to make sure it dies
      #(sleep 1; kill -9 ${CPID} >/dev/null 2>&1)&
      wait %2
    else
      wait %2
      RETVAL=$?
    fi
    return $RETVAL
) }

Answer 4

#! /bin/bash
timeout=10
interval=1
delay=3
(
    ((t = timeout)) || :

    while ((t > 0)); do
        echo "$t"
        sleep $interval
        # Check if the process still exists.
        kill -0 $$ 2> /dev/null || exit 0
        ((t -= interval)) || :
    done

    # Be nice, post SIGTERM first.
    { echo SIGTERM to $$ ; kill -s TERM $$ ; sleep $delay ; kill -0 $$ 2> /dev/null && { echo SIGKILL to $$ ; kill -s KILL $$ ; } ; }
) &

exec "$@"

Answer 5

Building on @loup's answer...

If you want to timeout a process and silence the kill job/pid output, run:

( (sleep 1 && killall program 2>/dev/null) &) && program --version 

This puts the backgrounded process into a subshell so you don't see the job output.

Answer 6

I prefer "timelimit", which has a package at least in debian.

http://devel.ringlet.net/sysutils/timelimit/

It is a bit nicer than the coreutils "timeout" because it prints something when killing the process, and it also sends SIGKILL after some time by default.