Questions tagged [trap]
The trap tag has no usage guidance.
140
questions
0
votes
1answer
21 views
Proper way to trap in zsh script
I'm having trouble getting a trap function in a shell-script to work without exiting the shell. I have a simple countdown timer that I want to be able to interrupt using ^C, and when I do I want the ...
0
votes
1answer
38 views
What is the difference between the single and double quotes used with the trap command?
I'm trying to learn how to use the signal trap command on Bash. The trap command is quite easy to use, but the issue that hangs in my head is the importance of using single and double quotes.
What is ...
1
vote
1answer
38 views
SNMPv3 traps in Zabbix
My question is about zabbix traps with SNMPv3 and snmptrapd service using zabbix_trap_receiver.pl. I have a switch on which I enabled SNMPv3 only, so the switch has no SNMPv1/2c rw or ro communities ...
0
votes
2answers
116 views
bash: experiment to save and restore global variable context
I made a small experiment to save in one line some context.
It works exactly as I wanted. So this post is:
1. to share it with the community.
2. to improve it, or have a complete other solution ...
0
votes
0answers
32 views
Bash Trap Handler Race Condition
I am playing with bash's trap feature. And the following script exhbits some kind of race condition.
#! /bin/bash
set -x
trap sigusr1 USR1
ANCESTOR_PID=$$
function sigusr1
{
num+=1
declare ...
1
vote
0answers
185 views
'unbound variable' error when using function-level bash trap (trap … RETURN)
Consider this script that calls into a function that sets up a trap for the RETURN of that function:
#!/usr/bin/env bash
set -euo pipefail
function f1() {
local temp_file
temp_file="$(mktemp)"
...
-1
votes
1answer
157 views
trap command not found [closed]
I run into this weird behavior of trap.
According to trap's manpage:
When a subshell is entered, traps that are not being ignored are set to the default actions. This does not imply that the trap ...
2
votes
0answers
105 views
Disabling “some” traps temporarily, and re-enabling them
I need to disable some(not all) of the traps temporarily in my function and then re-activate them. But I get an unexpected behaviour(I'm pretty new to traps and signals though) when I'm doing it:
...
1
vote
1answer
59 views
Can a program trap on memory access to certain regions of process memory?
I'm looking for a way to have an event get triggered and trapped when accessing a specific read-only section of a program's memory. Specifically, if I have a section of program memory that contains a ...
3
votes
1answer
266 views
What is the use of declare with option -t
If you call the command help declare. You will see the following information:
-t NAME : to make NAMEs have the `trace' attribute
Is there any example that demonstrates the use of this option. I ...
0
votes
1answer
99 views
Question about debug trap
I have a script as below:
function dbgtrap {
echo "badvar is $badvar"
}
badvar=0
function some_func {
badvar=1
badvar=2
badvar=3
}
set -o functrace
trap dbgtrap DEBUG
some_func
...
3
votes
2answers
263 views
EXIT Trap with POSIX
I have a script I wrote in Bash that I'm trying to modify to be POSIX-compliant. I have managed to get everything working except I cannot get the EXIT trap to trigger when the process is terminated ...
0
votes
1answer
917 views
unable to launch any program: trap int3 ip error
I cannot launch any program in my desktop environment. I get these errors in dmesg:
traps: terminator[3670] trap int3 ip:374dda71261 sp:388624bbec0 error:0
traps: pcmanfm[3685] trap int3 ip:...
2
votes
2answers
280 views
Bash ignoring SIGINT trap when 'select' loop is running
When i use 'trap' combined with select loop, namely when i try to hit CTRL+C to break out while options are displayed, it will just print ^C in terminal. If i remove 'trap' from script it will ...
0
votes
1answer
280 views
Use bash EXIT trap to confirm or cancel ctrl+d [duplicate]
Is there a simple way to require confirmation before logging out of a shell, and to prevent the shell from exiting if confirmation is denied? This would be useful to avoid accidentally terminating an ...
5
votes
1answer
212 views
How to make `trap` know if the EXIT is after successful program finish or because of premature as an error or something
PROBLEM:
I have a shell program that I have been writing but I can't find out how to make sure that trap is trapping for cleanup at the end or because of a error in some command, it cleans up either ...
0
votes
0answers
44 views
trap signal in bash initramfs fails to work
inside /init bash script executed by the kernel in initramfs.img i need to send a signal to drop me to a rescue shell, so i have
trap "exec /bin/bash" SIGINT
but ctrl+C isn't effective.
First why ...
0
votes
1answer
72 views
Deleting temporary direction via trap
I have a script which looks like this:
#!/bin/bash
set -e
tmpdir=$(mktemp -d)
pushd $tmpdir
trap 'popd && rm -rf $tmpdir' EXIT
# Business logic which may succeed or fail...
/bin/false
...
2
votes
1answer
91 views
Why does trap ERR behaviour differ over bash versions 3 and 4?
Background
Execute the following code in bash 3, 4 and 5 respectively, and you will get differing results.
(function handle_error () { echo ERROR; }; trap handle_error ERR; (exit 1))
Imagine that (...
1
vote
1answer
83 views
Signal trap from background job without pressing enter
In Bash 5 I ran into a situation where I want to do the following:
trap 'echo trapped!' USR1
while true; do kill -SIGUSR1 $$; sleep 1; done &
But I have to press enter on keyboard every time the ...
2
votes
3answers
446 views
How to signal a trap in “global” bash scope from function?
I want to execute a trap command in "global" scope, but the signal will come from within function. Of course it is possible to declare the variable globally beforehand or use the -g declare option. ...
2
votes
0answers
44 views
How to trigger a command after named pipe closes?
How can I execute some command after the named pipe has been readout in other end. I was trying to use trap. But nothing happens. My script is something like below.
#!/bin/sh
cleanup()
{
echo "...
2
votes
1answer
335 views
Failing on errors inside a function which is called on the left-hand-side of an && expression
I am working on a Bash script with several functions. I would like to exit the script if any commands return an nonzero exit code, unless in a context where that code is being explicitly handled (such ...
2
votes
1answer
346 views
using both trap and exec to redirect output to tee in bash
I have script that reads lines from a file, processes each line. I'd like to be able to do some "post-processing" in a way that even when the script didn't finish reading all lines because I pressed ...
0
votes
0answers
254 views
Interrupt signal names don't work over ssh: bad trap [duplicate]
If run over ssh, a script with a trap statement with interrupt signal names (SIGINT, etc) gives an error and the trap does not work when an interrupt (eg. Ctrl+C) is sent. Eg:
#!/bin/bash
trap '...
11
votes
3answers
2k views
Trap 'Ctrl + c' for bash script but not for process open in this script
I tried to have an interactive program in a bash script :
my_program
And I wish to be able to close it with 'Ctrl + c'.
But when I do it my script is closing as well.
I know about.
trap '' 2
...
0
votes
1answer
635 views
How to trace snmp trap sent by client process?
We have a process(should be a client program) on RHEL 7.4 that send snmp traps to a Solaris server that has trap receiver process(should be a server program listening on 162/1691) on other machine(...
2
votes
1answer
194 views
Killing background processes started in nix-shell
I am developing a simple data science environment with Python tools and a database. When I enter the nix-shell, I spin up the database process. I would like to spin it down when exiting the ...
2
votes
1answer
334 views
How to trap INT signal infinitely many times?
I'm piping output of an interactive command (ghci) through sed-based script to add some colors:
ghci | colorize.sh
where colorize.sh is something like:
#!/bin/bash
trap '' INT
sed '...some pattern.....
0
votes
1answer
2k views
wait for kill signal
In a bash script, is there a simple way to wait for a signal, something like:
wait -s SIGINT
or whatever? Maybe just trap?
3
votes
4answers
614 views
Delay termination of script
I have a script like this (written for /bin/sh on OpenBSD) which first updates a local copy of some CVS repositories using rsync, and then updates the checked-out version of these on my machine. The ...
2
votes
1answer
535 views
Trap and collect script output, “input file is output file” error?
I need to upload the output of the current script, so I added a trap and set -ex, e.g
#!/bin/bash
exec &> /tmp/error.log
trap 'cat /tmp/error.log; curl http://127.0.0.1/error.php?hostname=$(...
0
votes
3answers
990 views
exceptions to ERR trap
I am using an ERR trap to catch any error in my bash script and output what happened to log. (similar to this question: Trap, ERR, and echoing the error line ) It works as expected. The only problem ...
0
votes
1answer
121 views
Choices for dealing with a signal?
From APUE
A process has three choices for dealing with a signal.
Ignore the signal. This option isn’t recommended for signals that denote a hardware exception, such as ...
asked May 31 '18 at 3:56
StackExchange for All
67.1k100 gold badges321 silver badges608 bronze badges
1
vote
1answer
631 views
Why does bash exit immediately when waiting for a command to complete and receives SIGHUP for which a trap has been set?
From Bash manual
If Bash is waiting for a command to complete and receives a signal for
which a trap has been set, the trap will not be executed until the
command completes.
When Bash is ...
asked May 27 '18 at 22:03
StackExchange for All
67.1k100 gold badges321 silver badges608 bronze badges
2
votes
1answer
208 views
How to start Vim from a trap and still be able to resume it after suspending it?
I have the following code in my ~/.zshrc:
nv() (
if vim --serverlist | grep -q VIM; then
if [[ $# -eq 0 ]]; then
vim
elif [[ $1 == -b ]]; then
shift 1
IFS=' '
vim --...
0
votes
2answers
80 views
Which signal >(process) receives after main shell exits?
This is a Zshell question, although Bash, if it has >(command) syntax (i.e. process substitution of such kind), can hint a solution too. This really basic code explains all:
% fun() {
setopt ...
4
votes
2answers
575 views
Trap both INT and ERR, but callback got executed multiple times
I'm trapping both INT and ERR with the following code
set -ex -o pipefail
dest=$(mktemp -d)
cd "$dest"
trap "echo; echo Clean up; rm -rf $dest" INT ERR
sleep 9999
When I press ^C the clean up ...
0
votes
1answer
736 views
Why script that kill itself using a signal handler produce segmentation fault?
SCRIPT GOAL: the script is invoked as ./script.sh cmd1 cmd2 ... cmdn. It should executes in background all the commands passed as arguments from the command line and check when all of them have ...
0
votes
2answers
750 views
Trap all commands in function
I'm working with a set of scripts with functions treated as readonly.
The functions are more than just a list of commands, for example, there can be loops and change directories and even calls to ...
0
votes
1answer
354 views
trap is not catching HUP / SIGHUP [duplicate]
I have these bash function:
on_ql_trap(){
echo "foobar" > "$HOME/.quicklock/debug.json"
}
ql_trap(){
trap on_ql_trap EXIT;
trap on_ql_trap 0;
trap on_ql_trap SIGHUP;
trap on_ql_trap HUP;...
1
vote
1answer
359 views
Trap “break” not working while read command is being called
I have this bash-written hangman game for a school project, and currently I am trying to replace the ctrl-c exit command for a while loop break, so the user goes back from the actual game to the ...
1
vote
1answer
462 views
lock file not removed when trap is inside an “if”
I put my trap inside an if, run the script, and after that second execution, it warns that lock file is held (ok). But when I kill -9 the running PID, the lockfile is not removed.
When I move trap ...
1
vote
0answers
80 views
What determines a login shell's default trap handlers?
I have a linux box that when I login with ssh, both the keystroke Ctrl-C and manually sending SIGINT will directly terminates the session.
λ> ssh root@rhel74
Last login: Sun Mar 18 21:08:02 2018 ...
0
votes
0answers
250 views
trapping HUP/SIGHUP is not working in bash script
I have this bash script:
https://gist.github.com/ORESoftware/06dbb26a48d2ddf48a5a2166834e0836
when I call ql_acquire_lock in a shell, if I can call mkdir on a directory, then I acquire that lock. ...
2
votes
1answer
144 views
How to restrict interrupt signal to just the child process?
I have a bunch of log files and I want to do a tail -f on them in a loop such that when I press Ctrl-C, the current tail -f gets killed and I proceed to the next log file:
for log in *.log; do
...
1
vote
1answer
521 views
docker-compose, less and SIGINT
I have a script that boots up a test environment using docker-compose.
This script pipes the mixed stdout of many docker containers on stdout through less:
# This is part of a larger script with some ...
2
votes
1answer
358 views
Run subshells in parallel and collect exit codes
I have the following, I thought it ran the subshells in parallel, but it actually seems to run them in series, and I cannot figure out why:
#!/usr/bin/env bash
set -e;
set -m # allow for job control
...
0
votes
1answer
487 views
Trap handler not working?
Is sth wrong with the following trap?
trap cleanup SIGINT
cleanup() {
echo "Exiting script ..."
}
I never see the echo command when hitting Ctrl+c
The snippet is at the bottom ...
5
votes
2answers
2k views
RETURN trap in Bash not executing for function
I'm dabbling in traps in Bash again. I've just noticed the RETURN trap doesn't fire up for functions.
$ trap 'echo ok' RETURN
$ f () { echo ko; }
$ f
ko
$ . x
ok
$ cat x
$
As you can see it goes ...
