Question

Here is my shell script:

#!/bin/bash
PIDS=$(ps -e | grep $1 |grep -v grep| awk '{print $1}')
kill -s SIGINT $PIDS
echo "Done sendings signal"

I am passing the name of the process as command line argument.
The echo command is not getting executed, although the target processes are actually receiving the SIGINT signal and exited.

Any suggestions?

Update:
I changed the code to:

#!/bin/bash
PIDS=$(ps -e |grep $1 | grep -v grep | awk '{print $1}'|grep -v $$)
echo $PIDS
kill -s SIGINT $PIDS
echo "Done sendings signal"
echo "The current process is $$"

Now I am noticing a strange thing:
The script is working but not as expected. Executing following command in command line outside the script
ps -e|grep process-name|grep -v grep|awk '{print $1}'|grep -v $$
gives pid of the process-name but when I execute the same command inside shell script, assign it to variable PIDS and then echo PIDS then it shows one more pid in addition to the pid of process-name. Therefore when the kill command executes it gives an error that the process with second pid doesn’t exist. It does echo the remaining sentences in the terminal. Any clue ?

Answer 1

Your script works. The only reason I can see for the echo not being executed is that some value of $1 and the script file name combine so that your script PID is also gathered, thereby making the script suicide.

The PIDS line spawns a process running ps, grep, another grep — so you won’t find in PIDS the processes running grep, but what about the parent process itself?

Try:

#!/bin/bash
PIDS=$(ps -e | grep $1 |grep -v grep | awk '{print $1}' | grep -v "^$$\$" )
kill -s SIGINT $PIDS
echo "Done sendings signal"

or run the pipes one after the other with suitable safety greps.

Edit: it is evident that the “$1” selection is selecting too much. So I’d rewrite the script like this:

#!/bin/bash
# Gather the output of "ps -e". This will also gather the PIDs of this
# process and of ps process and its subshell.
PSS=$( ps -e )
# Extract PIDs, excluding this one PID and excluding a process called "ps".
# Don't need to expunge 'grep' since no grep was running when getting PSS.
PIDS=$( echo "$PSS" | grep -v "\<ps\>" | grep "$1" | awk '{print $1}' | grep -v "^$$\$" )
if [ -n "$PIDS" ]; then
    kill -s SIGINT $PIDS
else
    echo "No process found matching $1"
fi
echo "Done sending signal."