Is it possible to kill command on its first output?
Here is example of command
strace -e trace=desc ./a.out 2>&1 | grep "open\|something_else"
So I want to kill strace and/or a.out processes in case if grep finds something.
Is it possible in bash (or may be in python)?
You can use it to exit like this using awk:
strace -e trace=desc ./a.out 2>&1 | awk '/open|something_else/ {print; exit}'
Related
I'm currently monitoring a log file and my ultimate goal is to write a script that uses tail -n0 -f and execute a certain command once grep finds a correspondence. My current code:
tail -n 0 -f $logfile | grep -q $pattern && echo $warning > $anotherlogfile
This works but only once, since grep -q stops when it finds a match. The script must keep searching and running the command, so I can update a status log and run another script to automatically fix the problem. Can you give me a hint?
Thanks
use a while loop
tail -n 0 -f "$logfile" | while read LINE; do
echo "$LINE" | grep -q "$pattern" && echo "$warning" > "$anotherlogfile"
done
awk will let us continue to process lines and take actions when a pattern is found. Something like:
tail -n0 -f "$logfile" | awk -v pattern="$pattern" '$0 ~ pattern {print "WARN" >> "anotherLogFile"}'
If you need to pass in the warning message and path to anotherLogFile you can use more -v flags to awk. Also, you could have awk take the action you want instead. It can run commands via the system() function where you pass the shell command to run
I was running an ubuntu console, when I type the following command, all the processes would be perfectly killed.
kill -9 $(ps -ef | grep 'job1/' | grep -v grep| awk '{print $2}')
But when I was trying to use crontab to call a script routinely, things went wrong.
#!/bin/bash
pid=$(ps -ef | grep 'job1/' | grep -v grep | awk '{print $2}')
echo $pid
kill -9 $pid
# the following commands were never executed
sleep 5
/data/job1/tomcat8/bin/startup.sh
The result was just like this:
15432 15438
Killed
It seems to just killed the job, but won't execute the following commands. Any idea?
If you are going to make a script that kills things by PID then you need to be very careful that you kill the right things.
You already have grep -v grep to avoid killing the grep itself, but it seems that you have not put in anything to protect against the script killing itself. Since you know your own PID you could grep -v that, but what if you are 123 and one of the things you want to kill is 1234? Probably safer to go by script name.
How can I break a tail -f in bash? Since this question is related to this question
tail -f | awk and end tail once data is found
I tried the following:
#! /bin/bash
tvar="testing"
(set -o pipefail && tail -f <<< "$tvar" | awk '{print; exit} END{ exit 1}' )
But the script is still hanging on to tail -f
Well, the problem is not the tail -f but the awk which hangs. It is meant to terminate when EOF is found (with exit 1). But there is no EOF found; the tail -f does not terminate, so there comes no EOF.
Would the awk terminate, then this would also break the pipe and the tail would receive a SIGPIPE (which would terminate it).
You must find a different condition on which to terminate.
EDIT:
To achieve what you want you can start the tail -f in the background, remember its PID and kill it as soon as you do not need it anymore. Running in the background and using a pipe at the same time is tricky. The easiest way to do it would be to use a named pipe (FIFO):
mkfifo log.pipe
tail -f log > log.pipe & tail_pid=$!
awk ... < log.pipe
kill $tail_pid
rm log.pipe
It seems that switching from using <<< to echo "$tvar" | tail -f does what you want instead?
$> cat test.sh
#! /bin/bash
tvar="testing"
(set -o pipefail && echo "$tvar" | tail -f | awk '{print} END{ exit 1}' )
$> ./test.sh
testing
$>
Although the awk doesn't print anything out afterwards.
Okay so here's another one about the StarMade server.
Previously I had this script for detecting a crash, it would simply search through the logs:
#!/bin/bash
cd "$(dirname "$0")"
if ( grep "[SERVER] SERVER SHUTDOWN" log.txt.0); then
sleep 7; kill -9 $(ps -aef | grep -v grep | grep 'StarMade.jar' | awk '{print $2}')
fi
It would find "[SERVER] SERVER SHUTDOWN" and kill the process after that, however this is not a waterproof method, because with different errors it could be possible that the message doesn't appear, rendering this script useless.
So I have this tool that can send commands to the server, but returns an EOF exception when the server is in a crashed state. I basically want to grab the output of this command, and use it in the if-statement above, instead of the current grep command, in such a way that it would execute the commands below when the grep finds "java.io.EOFException".
I could make it write the output to a file and then grep it from there, but I wonder, isn't there a better/more efficient method to do this?
EDIT: okay, so after a bit of searching I put together the following:
if ( java -jar /home/starmade/StarMade/StarNet.jar xxxxx xxxxx /chat) 2>&1 > /dev/null |grep java.io.EOFException);
Would this be a valid if-statement? I need it to match "java.io.EOFException" in the output of the first command, and if it matches, to execute something with "then" (got that part working).
Not sure to solve your problem, but this line:
ps -aef | grep -v grep | grep 'StarMade.jar' | awk '{print $2}'
could be change to
ps -aef | awk '/[S]tarMade.jar/ {print $2}'
The [S] prevents awk from finding itself.
Or just like this to get the pid
pidof StarMade.jar
I want to do a tail -F on a file until matching a pattern. I found a way using awk, but IMHO my command is not really clean. The problem is that I need to do it in only one line, because of some limitations.
tail -n +0 -F /tmp/foo | \
awk -W interactive '{if ($1 == "EOF") exit; print} END {system("echo EOF >> /tmp/foo")}'
The tail will block until EOF appears in the file. It works pretty well. The END block is mandatory because awk's exit does not exit right away. It makes awk to eval the END block before quitting. The END block hangs on a read call (because of tail), so the last thing I need to do, is to write another line in the file to force tail to exit.
Does someone know a better way to do that?
Use tail's --pid option and tail will stop when the shell dies. No need to add extra to the tailed file.
sh -c 'tail -n +0 --pid=$$ -f /tmp/foo | { sed "/EOF/ q" && kill $$ ;}'
Try this:
sh -c 'tail -n +0 -f /tmp/foo | { sed "/EOF/ q" && kill $$ ;}'
The whole command-line will exit as soon as the "EOF" string is seen in /tmp/foo.
There is one side-effect: the tail process will be left running (in the background) until anything is written to /tmp/foo.
I've not results with the solution:
sh -c 'tail -n +0 -f /tmp/foo | { sed "/EOF/ q" && kill $$ ;}'
There is some issue related with the buffer because if there aren't more lines appended to the file, then sed will not read the input. So, with a little more research i came up with this:
sed '/EOF/q' <(tail -n 0 -f /tmp/foo)
The script is in https://gist.github.com/2377029
This is something Tcl is quite good at. If the following is "tail_until.tcl",
#!/usr/bin/env tclsh
proc main {filename pattern} {
set pipe [open "| tail -n +0 -F $filename"]
set pid [pid $pipe]
fileevent $pipe readable [list handler $pipe $pattern]
vwait ::until_found
catch {exec kill $pid}
}
proc handler {pipe pattern} {
if {[gets $pipe line] == -1} {
if {[eof $pipe]} {
set ::until_found 1
}
} else {
puts $line
if {[string first $pattern $line] != -1} {
set ::until_found 1
}
}
}
main {*}$argv
Then you'd do tail_until.tcl /tmp/foo EOF
Does this work for you?
tail -n +0 -F /tmp/foo | sed '/EOF/q'
I'm assuming that 'EOF' is the pattern you're looking for. The sed command quits when it finds it, which means that the tail should quit the next time it writes.
I suppose that there is an outside chance that tail would hang around if the pattern is found at about the end of the file, waiting for more output to appear in the file which will never appear. If that's really a concern, you could probably arrange to kill it - the pipeline as a whole will terminate when sed terminates (unless you're using a funny shell that decides that isn't the correct behaviour).
Grump about Bash
As feared, bash (on MacOS X, at least, but probably everywhere) is a shell that thinks it needs to hang around waiting for tail to finish even though sed quit. Sometimes - more often than I like - I prefer the behaviour of good old Bourne shell which wasn't so clever and therefore guessed wrong less often than Bash does. dribbler is a program which dribbles out messages one per second ('1: Hello' etc in the example), with the output going to standard output. In Bash, this command sequence hangs until I did 'echo pqr >>/tmp/foo' in a separate window.
date
{ timeout -t 2m dribbler -t -m Hello; echo EOF; } >/tmp/foo &
echo Hi
sleep 1 # Ensure /tmp/foo is created
tail -n +0 -F /tmp/foo | sed '/EOF/q'
date
Sadly, I don't immediately see an option to control this behaviour. I did find shopt lithist, but that's unrelated to this problem.
Hooray for Korn Shell
I note that when I run that script using Korn shell, it works as I'd expect - leaving a tail lurking around to be killed somehow. What works there is 'echo pqr >> /tmp/foo' after the second date command completes.
Here's an extended version of Jon's solution which uses sed instead of grep so that the output of tail goes to stdout:
sed -r '/EOF/q' <( exec tail -n +0 -f /tmp/foo ); kill $! 2> /dev/null
This works because sed gets created before tail so $! holds the PID of tail
The main advantage of this over the sh -c solutions is that killing a sh seems to print something to the output such as 'Terminated' which is unwelcome
sh -c 'tail -n +0 --pid=$$ -f /tmp/foo | { sed "/EOF/ q" && kill $$ ;}'
Here the main problem is with $$.
If you run command as is, $$ is set not to sh but to the PID of the current shell where command is run.
To make kill work you need to change kill $$ to kill \$$
After that you can safely get rid of --pid=$$ passed to tail command.
Summarising, following will work just fine:
/bin/sh -c 'tail -n 0 -f /tmp/foo | { sed "/EOF/ q" && kill \$$ ;}
Optionally you can pass -n to sed to keep it quiet :)
To kill the dangling tail process as well you may execute the tail command in a (Bash) process substituion context which can later be killed as if it had been a backgrounded process. (Code taken from How to read one line from 'tail -f' through a pipeline, and then terminate?).
: > /tmp/foo
grep -m 1 EOF <( exec tail -f /tmp/foo ); kill $! 2> /dev/null
echo EOF > /tmp/foo # terminal window 2
As an alternative you could use a named pipe.
(
: > /tmp/foo
rm -f pidfifo
mkfifo pidfifo
sh -c '(tail -n +0 -f /tmp/foo & echo $! > pidfifo) |
{ sed "/EOF/ q" && kill $(cat pidfifo) && kill $$ ;}'
)
echo EOF > /tmp/foo # terminal window 2
ready to use for tomcat =
sh -c 'tail -f --pid=$$ catalina.out | { grep -i -m 1 "Server startup in" && kill $$ ;}'
for above scenario :
sh -c 'tail -f --pid=$$ /tmp/foo | { grep -i -m 1 EOF && kill $$ ;}'
tail -f <filename> | grep -q "<pattern>"