Questions tagged [trap]
The trap tag has no usage guidance.
0
votes
1answer
25 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 ...
-1
votes
1answer
63 views
Is the term trap (of Bash) more accurate than the generic “callback” term in programming? [closed]
Please consider:
scripttmp=$(mktemp -d)
cleanup() {
rm -rf "${scripttmp}"
}
trap cleanup EXIT
I understand cleanup is a "call(ed)back" function as it's being called just before exiting from ...
4
votes
1answer
86 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
30 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
18 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
45 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
43 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
2answers
74 views
How can I 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
36 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
53 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
137 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
90 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
1k 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
294 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(...
1
vote
1answer
56 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
148 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
573 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?
4
votes
4answers
375 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
347 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
440 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
77 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 ...
1
vote
1answer
377 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 ...
2
votes
1answer
120 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
58 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 ...
5
votes
2answers
257 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
296 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
539 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
221 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
181 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
248 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
65 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
161 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
98 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
362 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
215 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
280 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 ...
4
votes
2answers
957 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 ...
3
votes
0answers
81 views
DEBUG trap statement in ksh93 not executed after first run if it contains exit or return statements
I was trying to write a simple function that checks if a config file is "sanitized" and safe for sourcing or not. I seemingly got it to work in bash, and in ksh (Version ABIJM 93v- 2014-06-25) in the ...
2
votes
0answers
234 views
trapping signals without interfering with other signals
When trapping a signal in a shell script, the trap commands are not executed until the current command finishes. For example, consider the following shell script:
#!/bin/bash
trap 'echo "SIGTERM ...
0
votes
1answer
54 views
How can I test that the bash interactive shell handles the signal using the handler that I set up via `trap`?
In a bash interactive shell, when I run a trap command (e.g. trap "echo You hit control-C!" INT) to set up a signal handler, does that set up how the bash interactive shell handles the signal?
How ...
2
votes
1answer
472 views
Trap does not catch SIGTERM in child script
I have two scripts. First one is basically wrapper that calls subscript and sets timeout.
#!/bin/bash
# wrapper_script
timeout --signal=SIGTERM 50 main_script.sh
And if execution of main_script.sh ...
1
vote
0answers
1k views
Restoring tty correctly with stty
I'm writing a bash script to read some user input (like a password request), and I'd like to capture the result and pass it through its stdout.
(I'm working in a GNU/Linux environment, with recent ...
2
votes
1answer
51 views
Output signal in trap which caused the trap being called?
Let's say I have the following trap, which catches some signals, which terminate the script:
#!/bin/sh
trapterm() {
echo "Process (PID: $$) interrupted." >&2
exit 2
}
# add trap to ...
2
votes
0answers
41 views
`trap n condition` syntax
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#trap :
trap n [condition...] trap [action condition...]
If the first operand is an unsigned decimal integer, the shell ...
0
votes
1answer
99 views
Can I capture trap messages along with $LINE_NO?
I have a code like:
trap 'error ${LINENO} ${BASH_COMMAND}' ERR
I want to capture error message along with this. Is there any built-in variable for printing error message?
4
votes
0answers
543 views
sometimes a trap-and-continue-a-for-loop on ctrl-c in bash doesn't continue [closed]
I have the following trap defined in my (long) script:
#!/usr/bin/env bash
function continue_on_ctrl_c() {
echo "** CTRL-C trapped **"
continue # jump to the next iteration in the ...
1
vote
1answer
241 views
Shell scripts connected with pipe: trap termination of one script
I have two shell scripts, one runs on a server and writes some files to a temporary directory. This directory is then sent as a tar archive to stdout. At the end (or when it gets interrupted), the ...
2
votes
2answers
385 views
Reset STDOUT FD in trap
Script
#!/usr/bin/env bash
# Exit on error. Append "|| true" if you expect an error.
set -o errexit
# Exit on error inside any functions or subshells.
set -o errtrace
# Do not allow use of undefined ...
3
votes
0answers
6k views
How to configure snmptrapd to process incoming traps from a Juniper device?
I have a CentOS server (7.2). I am trying to configure this as a SNMP trap receiver.
In my snmptrapd configuration, I am calling a very basic shell script just to identify if the trap was received:
[...
5
votes
3answers
2k views
Strange problem with trap and SIGINT
Please explain this:
#!/bin/bash
# This is scripta.sh
./scriptb.sh &
pid=$!
echo $pid started
sleep 3
while true
do
kill -SIGINT $pid
echo scripta.sh $$
sleep 3
done
-
#!/bin/bash
#...
