Waiting for background processes to finish before exiting script

If you want to wait for jobs to finish, use wait. This will make the shell wait until all background jobs complete. However, if any of your jobs daemonize themselves, they are no longer children of the shell and wait will have no effect (as far as the shell is concerned, the child is already done. Indeed, when a process daemonizes itself, it does so by terminating and spawning a new process that inherits its role).

#!/bin/sh{ sleep 5; echo waking up after 5 seconds; } &{ sleep 1; echo waking up after 1 second; } &waitecho all jobs are done!

You can use kill -0 for checking whether a particular pid is running or not.

Assuming, you have list of pid numbers in a file called pid in pwd

while true;do     if [ -s pid ] ; then        for pid in `cat pid`        do              echo "Checking the $pid"            kill -0 "$pid" 2>/dev/null || sed -i "/^$pid$/d" pid        done    else        echo "All your process completed" ## Do what you want here... here all your pids are in finished stated        break    fidone

WARNING: Long script ahead.

A while ago, I faced a similar problem: from a Tcl script, launch a number of processes, then wait for all of them to finish. Here is a demo script I wrote to solve this problem.

main.tcl

#!/usr/bin/env tclsh# Launches many processes and wait for them to finish.# This script will works on systems that has the ps command such as# BSD, Linux, and OS Xpackage require Tclx; # For process-management utilitiesproc updatePidList {stat} {    global pidList    global allFinished    # Parse the process ID of the just-finished process    lassign $stat processId howProcessEnded exitCode    # Remove this process ID from the list of process IDs    set pidList [lindex [intersect3 $pidList $processId] 0]    set processCount [llength $pidList]    # Occasionally, a child process quits but the signal was lost. This    # block of code will go through the list of remaining process IDs    # and remove those that has finished    set updatedPidList {}    foreach pid $pidList {        if {![catch {exec ps $pid} errmsg]} {            lappend updatedPidList $pid        }    }    set pidList $updatedPidList    # Show the remaining processes    if {$processCount > 0} {        puts "Waiting for [llength $pidList] processes"    } else {        set allFinished 1        puts "All finished"    }}# A signal handler that gets called when a child process finished.# This handler needs to exit quickly, so it delegates the real works to# the proc updatePidListproc childTerminated {} {    # Restart the handler    signal -restart trap SIGCHLD childTerminated    # Update the list of process IDs    while {![catch {wait -nohang} stat] && $stat ne {}} {        after idle [list updatePidList $stat]    }}## Main starts here#puts "Main begins"set NUMBER_OF_PROCESSES_TO_LAUNCH 10set pidList {}set allFinished 0# When a child process exits, call proc childTerminatedsignal -restart trap SIGCHLD childTerminated# Spawn many processesfor {set i 0} {$i < $NUMBER_OF_PROCESSES_TO_LAUNCH} {incr i} {    set childId [exec tclsh child.tcl $i &]    puts "child #$i, pid=$childId"    lappend pidList $childId    after 1000}# Do some processingputs "list of processes: $pidList"puts "Waiting for child processes to finish"# Do some more processing if required# After all done, wait for all to finish before exitingvwait allFinishedputs "Main ends"

child.tcl

#!/usr/bin/env tclsh# child script: simulate some lengthy operationsproc randomInteger {min max} {    return [expr int(rand() * ($max - $min + 1) * 1000 + $min)]}set duration [randomInteger 10 30]puts "  child #$argv runs for $duration miliseconds"after $durationputs "  child #$argv ends"

Sample output for running main.tcl

Main beginschild #0, pid=64525  child #0 runs for 17466 milisecondschild #1, pid=64526  child #1 runs for 14181 milisecondschild #2, pid=64527  child #2 runs for 10856 milisecondschild #3, pid=64528  child #3 runs for 7464 milisecondschild #4, pid=64529  child #4 runs for 4034 milisecondschild #5, pid=64531  child #5 runs for 1068 milisecondschild #6, pid=64532  child #6 runs for 18571 miliseconds  child #5 endschild #7, pid=64534  child #7 runs for 15374 milisecondschild #8, pid=64535  child #8 runs for 11996 miliseconds  child #4 endschild #9, pid=64536  child #9 runs for 8694 milisecondslist of processes: 64525 64526 64527 64528 64529 64531 64532 64534 64535 64536Waiting for child processes to finishWaiting for 8 processesWaiting for 8 processes  child #3 endsWaiting for 7 processes  child #2 endsWaiting for 6 processes  child #1 endsWaiting for 5 processes  child #0 endsWaiting for 4 processes  child #9 endsWaiting for 3 processes  child #8 endsWaiting for 2 processes  child #7 endsWaiting for 1 processes  child #6 endsAll finishedMain ends