LinuxQuestions.org - [SOLVED] How to terminate while loop.

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How to terminate while loop.

Hi

I started a while loop directly from terminal to read a file line by line and to run a command on each line. Post running the command I realized to modify the command and tried to stop the loop by using CTRL+C but it didn't stop. I closed that terminal directly but loop is still running. I also tried to KILL the process but it is getting started automatically with a new PID. Please suggest to stop this loop.

Thanks.

kill the parent process, probably a bash shell.

How did you start the while loop?

What I did is I searched the PID for the command running on each line and killed the same. Please suggest, how to kill parent process.

while read line
do
ldapsearch $line
done < filename

pstree -p will show the parents with their PIDs

Use the pstree command to find the parent process, e.g.

Code:

pstree -p username

specifying your username to reduce the output.

Edit: Beaten by catkin for a bunch of seconds! ;)

Hi Charles! :)

Quote:

Originally Posted by satishchahar (Post 4640451)

while read line
do
ldapsearch $line
done < filename

It's not obvious why that doesn't respond to multiple Ctrl+C signals, unless the ldapsearch command is programmed to ignore SIGINT.

EDIT: and doesn't exit

Quote:

Originally Posted by satishchahar (Post 4640451)

while read line
do
ldapsearch $line
done < filename

Have you tried to rename or move filename?

Quote:

Originally Posted by colucix (Post 4640454)

Edit: Beaten by catkin for a bunch of seconds! ;)

Hi Charles! :)

Hi colucix :)

We keep doing that, one way round or the other

Hi colucix

I killed the parent process but process is still running with a new parent ID.
Also tried to move the filename.

Try killing the parent's parent

Killing the parent process, didn't help.

Assuming you are not logged on as root, try killing the parent's parent and, if that doesn't work, the parent's parent's parent

Quote:

.. terminal to read a file line by line and to run a command on each line. P ..

Also

Quote:

I also tried to KILL the process but it is getting started automatically with a new PID

Could we see the culprit script?

If it is not a live system, then shutdown -h now or shutdown -g0
`

OK.

Quote:

Originally Posted by catkin (Post 4640455)

It's not obvious why that doesn't respond to multiple Ctrl+C signals, unless the ldapsearch command is programmed to ignore SIGINT.

Or the process group isn't in the foreground, or it otherwise isn't associated with the same session as the shell. Or if a process has disabled the bindings that cause the signal to be sent from the terminal to the foreground process group. Or the process is in an uninterruptible sleep. A problem with the hard drive could cause that to happen in the "read" loop.
Kevin Barry

Check out these new functions that I just made. They might be helpful.

Code:

#!/bin/bash





# void killtree (uint <parent_pid>, [string <signal>])

#

# Creates a list of processes first then sends the signal to all of

# them synchronously.

#

function killtree {

        listtree "$1"

        kill -s "${2:-SIGTERM}" "${__A0[@]}"

}





# void killtree2 (uint <parent_pid>, [string <signal>])

#

# This version kills processes as it goes.

#

function killtree2 {

        killtree2_ "$1" "${2:-SIGTERM}"

}





# void killtree2_ (uint <pid>, string signal)

#

function killtree2_ {

        local -a LIST=()

        read -a LIST < <(exec pgrep -P "$1")

        kill -s "$2" "$1"

        if [[ ${#LIST[@]} -gt 0 ]]; then

                local A

                for A in "${LIST[@]}"; do

                        killtree2_ "$A" "$2"

                done

        fi

}





# void killtree3 (uint <parent_pid>, [string <signal>])

#

# This version kills child processes first before the parent.

#

function killtree3 {

        killtree3_ "$1" "${2:-SIGTERM}"

}





# void killtree3_ (uint <pid>, string signal)

#

function killtree3_ {

        local -a LIST=()

        if read -a LIST < <(exec pgrep -P "$1"); then

                local A

                for A in "${LIST[@]}"; do

                        killtree3_ "$A" "$2"

                done

        fi

        kill -s "$2" "$1"

}





# void killchildren (uint <parent_pid>, [string <signal>])

#

# Creates a list of child processes first then sends the signal to all

# of them synchronously.

#

function killchildren {

        listchildren "$1"

        kill -s "${2:-SIGTERM}" "${__A0[@]}"

}





# void killchildren2 (uint <parent_pid>, [string <signal>])

#

# This version kills processes as it goes.

#

function killchildren2 {

        local -a LIST=()

        read -a LIST < <(exec pgrep -P "$1")

        local A SIGNAL="${2:-SIGTERM}"

        for A in "${LIST[@]}"; do

                killtree2_ "$A" "$SIGNAL"

        done

}





# void killchildren3 (uint <parent_pid>, [string <signal>])

#

# This version kills child processes first before the parent.

#

function killchildren3 {

        local -a LIST=()

        read -a LIST < <(exec pgrep -P "$1")

        local A SIGNAL="${2:-SIGTERM}"

        for A in "${LIST[@]}"; do

                killtree3_ "$A" "$SIGNAL"

        done

}





# void listtree (uint <pid>)

#

# > uint array __A0 = list of PIDs

#

function listtree {

        __A0=("$1")

        listchildren_ "$1"

}





# void listchildren (uint <pid>)

#

# > uint array __A0 = list of PIDs

#

function listchildren {

        __A0=()

        listchildren_ "$1"

}





# void listchildren_ (uint <pid>)

#

function listchildren_ {

        local -a ADD=()

        if read -a ADD < <(exec pgrep -P "$1"); then

                local A I=${#__A0[@]}

                for A in "${ADD[@]}"; do

                        __A0[I++]=$A

                        listchildren_ "$A"

                done

        fi

}

Quote:

Originally Posted by ta0kira (Post 4641638)

Thanks Kevin -- that's comprehensive :)

Apart from the "hard drive problem" (which I don't understand but would like to know more about), the bash command shown would not do any of those so it would have to be ldapsearch command ... yes?

Quote:

Originally Posted by catkin (Post 4641791)

Apart from the "hard drive problem" (which I don't understand but would like to know more about)

An uninteruptible sleep is usually caused by hardware, since interrupting hardware requests can damage things. One of my old computers had a problem with the drive where it couldn't read/write properly in a certain part, and any process attempting to access that part couldn't be killed even by root with SIGKILL. This also might have also been a problem with the driver or the filesystem, though.

Quote:

Originally Posted by catkin (Post 4641791)

the bash command shown would not do any of those so it would have to be ldapsearch command ... yes?

My first thought was that we're missing some important context like, "oh yeah... I forgot to say I started the script with setsid," or something else that might prevent Ctrl+C from getting to the bash loop. If OP actually typed the posted loop as-is into a terminal that hasn't been reconfigured, then what you say is probably correct.
Kevin Barry

Sometimes CTRL-C isn’t working, maybe because it’s trapped or whatever. But a CTRL-Z succeeds and than you can either kill %1 of bg %1 at your convenience.

Quote:

Originally Posted by satishchahar (Post 4640428)

Perhaps ctrl/z would work. Of course, I never start loop directely from terminal, but it works when executing programs made executable by g++, and for other blocking situations at runing programs.

I never star a loop from terminal. But, when I run C++ programs and a loop is infinite (the condition to stop the loop is never true), and for other blocking situations I use ctrl/z.

Now loop has been completed and terminated automatically. Thanks anyway.