On Ctrl+C, kill the current command but continue executing the script

Question

I have a bash script, wherein I execute a line, sleep for sometime and then tail -f my log file to verify a certain pattern is seen, I press ctrl +c to get out of tail -f and then move to the next line till the bash script finishes execution:

Here is what I have done thus far:

#!/bin/bash


# capture the hostname
host_name=`hostname -f`


# method that runs tail -f on log_file.log and looks for pattern and passes control to next line on 'ctrl+c'

echo "==================================================="
echo "On $host_name: running some command"
some command here

echo "On $host_name: sleeping for 5s"
sleep 5

# Look for: "pattern" in log_file.log
# trap 'continue' SIGINT
trap 'continue' SIGINT
echo "On $host_name: post update looking for pattern"
tail -f /var/log/hadoop/datanode.log | egrep -i -e "receiving.*src.*dest.*"


# some more sanity check 
echo "On $host_name: checking uptime on process, tasktracker and hbase-regionserver processes...."
sudo supervisorctl status process


# in the end, enable the balancer
# echo balance_switch true | hbase shell

The script works but I get the error, what needs to change/ what am I doing wrong?

./script.sh: line 1: continue: only meaningful in a `for', `while', or `until' loop

Solution 1

The continue keyword doesn't mean whatever you think it means. It means continue to the next iteration of a loop. It makes no sense outside of a loop.

I think you're looking for

trap ' ' INT

Since you don't want to do anything upon reception of the signal (beyond killing the foreground job), put no code in the trap. You need a non-empty string, because the empty string has a special meaning: it causes the signal to be ignored.

Solution 2

The error arise due to trap 'continue' SIGINT. From help trap:

ARG is a command to be read and executed when the shell receives the signal(s) SIGNAL_SPEC

So your script try to do continue command when receive SIGINT call but the continue is used in loops only.

Comments

[pestophagous]

also potentially relevant to visitors of this page: unix.stackexchange.com/questions/163561/…

[Stéphane Chazelas]

Or trap : INT

[Amir Uval]

Also note that the trap must be before the line you need to break