Time Counter in a Shell Script

I want to execute a command at every 2 seconds and another command at every 5 secs in a while loop.

start
while [ 1 ]
do
if [ time diff == 2]
   do sth
fi 
if [ time diff == 5]
   do sth else
fi
end
dif = end - start

But this is a little problem when difference is 0. How can i do similar to this in 开发者_开发技巧a shell script?

Try this:

while true; do sth ; sleep 2 ; done

You can use a subshell:

#!/bin/bash

(while true ; do echo time2 ; sleep 2 ; done)&
(while true ; do echo time5 ; sleep 5 ; done)

However, you will have to do something to kill the background subshell later.

try sleep

while true
do
  ..
  sleep 2
done

possibly the simplest approach is a 10 second loop like this! (since 10 is the lowest common denominator of 2 and 5)

while true
do
    sth
    sleep 2
    sth
    sleep 1
    sth else
    sleep 1
    sth
    sleep 2
    sth
    sleep 2
    sth
    sth else
    sleep 2
done

It's a bit crazy though!

Of course this assume the commands are instant, you may want to background them with &

If you wanted to be very very thorough, you could use this as a starting point

#!/bin/bash

declare -a JOBPIDS

function repeatbackground()
{
    local delay="$1"
    shift
    (
        while true
        do
            sleep "$delay" || return 0 # abort on sleep interrupted
            eval "$@"
        done
    )&
    JOBPIDS=( ${JOBPIDS[@]-} $! )
}

function signalbackgroundtasks()
{
    for bgpid in "${JOBPIDS[@]}"
    do
        kill -TERM "$bgpid" || echo "Job $bgpid already vanished"
    done
    JOBPIDS=( )
}

trap "signalbackgroundtasks; exit 0" EXIT
repeatbackground 2 echo "by the other way"
repeatbackground 5 echo the other background job

echo "Running background jobs ${JOBPIDS[@]}"
wait
exit 0

#!/bin/bash
#
rhythm () {

    beat1=$1
    beat2=$2
    tick=0
    while [ 1 ]
    do
        (( tick % $beat1)) || echo a
        (( tick % $beat2)) || echo b
        tick=$(((tick+1)%(beat1*beat2)))
        sleep 1
    done 
}

rhythm 2 5 

This works, of course, only for 2 parameters, and if the the time consumed by echo in the example/ the real command in real, is insignificant.

The following doesn't use bash-specific features or subshells and is easy to generalize:

set 1 2 3 4 5
while :; do
  sleep 1
  shift  
  case $1 in
    2|4) echo "every 2 seconds" ;;
    5)   echo "every 5 seconds" ; set 1 2 3 4 5 ;;
  esac
done