Questions tagged [trap]
The trap tag has no usage guidance.
162
questions
1
vote
1
answer
40
views
Why does a command with a non-zero exit status send an ERR signal even when it is “part of a && or || list”?
man bash includes this documentation for using trap:
trap [-lp] [[arg] sigspec ...]
…
The ERR trap is not executed if the failed command is part of the command list
immediately following a ...
- 288
0
votes
0
answers
61
views
BASH - Getting stderr message into a variable to be passed to a trap
My question is relative to Ubuntu 20.04 where I am performing these tasks.
I currently pass some state information to a debug trap such as $BASH_COMMAND, $LINENO and $?. I would like to pass any ...
user516113
1
vote
1
answer
60
views
bash script print stderr on failure
I am trying to make the bash script silent if everything goes fine but print out all the stderr and debug info if it crashes for some reason.
Below is what I have so far.
#!/usr/bin/bash
set -e
rm -...
- 4,039
0
votes
2
answers
129
views
How do you continue execution after using trap EXIT in bash?
Environment: GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin20)
I'm attempting to trap the exit from another function but then continue executing the program. In an object oriented language ...
- 125
1
vote
1
answer
115
views
Setting a trap for INT doesn't work in a subshell
$ bash -c "trap \"echo INT\" INT; sleep 3" & pid=$!; sleep 1; kill -INT $pid; wait
[1] 27811
INT
[1]+ Done bash -c "trap \"echo INT\" INT; ...
- 2,893
0
votes
0
answers
58
views
EXIT trap is ignored on Ctrl-C when PID == 1
a.sh:
trap 'echo cleanup' EXIT
sleep 3
To reproduce, press Ctrl-C before the script finishes:
$ docker run --rm -itv $PWD:/app -w /app alpine:3.14 sh a.sh
^Ccleanup
$ docker run --rm -itv $PWD:/app -...
- 2,893
0
votes
0
answers
54
views
Shell, traps, signals and conditional cleanup
I have a script running qemu-system in background (-daemonize) and have to clean up (kill) running qemu-system once foreground process completes. Same time I have NOT to clean up (kill) running qemu-...
- 228
1
vote
2
answers
305
views
BASH: Change exit status in trap
Can I assign a different exit status to a shell script in a trap handler?
Through trial-and-error, I found that calling exit in trap the exit status can be changed. Normal commands, whether fail or ...
- 409
1
vote
1
answer
135
views
trap "ctrl-c" to kill background shell
background
bash 4.2
I have two files envar and main.sh
envar
...
# displays a spinner so that user knows the job is under processing.
spinner()
{
spin='-\|/'
i=0
while kill -0 $1 2>/dev/...
- 147
0
votes
0
answers
134
views
Ignore SIGHUP with trap while still being able to receive output and send input
So i already know one can ignore HUP by doing:
trap "command" HUP
but since that completely background the process, is it possible to do the same but still being able to send input to said ...
- 1,827
0
votes
1
answer
141
views
Bash trap wrong $BASH_COMMAND
I created two traps
trap function1 DEBUG
trap pwd ERR
function function1 {
echo $BASH_COMMAND
}
If I use some wrong command let's say a, then output is->
a
bash: a: command not found
a
/home/user/...
- 5,410
0
votes
1
answer
83
views
Bash: adding history -a to PROMPT_COMMAND makes incorrect calculation of last command's wall time
To calculate last command's wall time I use this code (code #1):
#
# Taken from https://stackoverflow.com/a/34812608/9881330
# Slightly modified.
#
function timer_now {
date +%s%N
}
function ...
- 355
0
votes
1
answer
201
views
Why do trap sometimes ignore signals?
I have the following script
#! /usr/bin/bash
trap "{ echo bye ;}" SIGINT
while :
do
echo "Hello"
done
When I press Ctrl-C the while loop is not stopped and echo ...
- 3,939
2
votes
1
answer
722
views
How to trap EXIT unconditionally (even if interrupted), in Zsh?
I would like to trap the exit hook of a function. Bash provides a nice signal called RETURN (non-POSIX) which get called when a function returns, such as
function test_trap() {
trap 'echo trapped' ...
- 1,073
0
votes
0
answers
79
views
Gracefully terminate the executing line of a bash script
The manual workflow I want to automate is as follows:
$> adb shell screenrecord /sdcard/file.mp4
This starts a recording on a connected Andfroid device and writes it on the device's sd card. This ...
- 159
0
votes
2
answers
772
views
Is the sigspec for 0 EXIT or SIGEXIT or exit?
I need to write a trap which tracks when a process exits (amongst other things) and removes a temporary file. I'd prefer to use the sigspec instead of number for better code readability, the relevant ...
- 654
1
vote
1
answer
324
views
Trap SIGPIPE upon writing to FIFO
These are the steps to reproduce the problem.
writer:
#!/bin/bash
trap 'echo NoReader!' PIPE
cat > fifo
Open two terminals.
I will denote them by the >T1< and >T2< headers below,
and ...
- 17.3k
4
votes
2
answers
404
views
trapped in bash traps (RETURN trap)
I am looking for an idiomatic pattern to use traps as a meaning "ensure" or "finally", so they should execute no matter how a bash function exits.
I've found the RETURN trap, but ...
- 388
2
votes
0
answers
173
views
Trap on DEBUG signal for the ash and dash shells?
With the bash shell, you can install a trap on the synthetic DEBUG signal. This is useful and will execute your function or bit of code on every shell command.
Not so in ash or dash.
$ trap 'echo hi' ...
- 162
2
votes
0
answers
48
views
Why does trap not get triggered when sourcing a file that does not exist?
#!/bin/bash
set -eEuo pipefail
set -x
function deploy_cleanup(){
echo "---Cleaning up---"
echo "hello"
}
trap deploy_cleanup ERR
whoami
source euaueoaue
Outputs:
+ ...
- 4,025
1
vote
1
answer
651
views
Termination of ssh with Ctrl-C trap in bash script
When I press Ctrl+C with the first script, it works as I expect, Ctrl+C doesn't have any effect
#!/bin/bash
trap '' INT
ssh user@server 'svn checkout ...'
echo "done"
But with the second script Ctrl+...
- 13
0
votes
0
answers
27
views
Strange behavior of bash and SIGTERM with Ubuntu [duplicate]
Here's what happens in Ubuntu (Linux ubuntu 5.3.0-53-generic #47~18.04.1-Ubuntu SMP Thu May 7 13:10:50 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux, bash 4.4.20(1)):
In Terminal, open a window (let's call ...
- 89
2
votes
2
answers
210
views
Capture bash function's result and allow it to exit
This function should exit the calling script:
crash() {
echo error
exit 1
}
This works as expected:
echo before
crash
echo after # execution never reaches here
But this does not:
echo ...
- 1,413
2
votes
1
answer
2k
views
Proper way to trap in zsh script
I'm having trouble getting a trap function in a zsh shell-script to work without exiting the shell. I have a simple countdown timer that I want to be able to interrupt using Ctrl+C, and when I do I ...
- 141
1
vote
1
answer
316
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 ...
- 1,072
1
vote
1
answer
840
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 ...
- 74
0
votes
2
answers
908
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 ...
- 461
0
votes
0
answers
169
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 ...
- 101
1
vote
0
answers
2k
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)"
...
- 491
1
vote
1
answer
1k
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 ...
- 591
2
votes
0
answers
569
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:
...
- 471
1
vote
1
answer
433
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 ...
- 23
5
votes
1
answer
615
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 ...
- 159
0
votes
1
answer
585
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
...
- 159
7
votes
3
answers
2k
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 ...
- 71
3
votes
2
answers
3k
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:...
- 563
4
votes
2
answers
1k
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 ...
- 347
0
votes
1
answer
1k
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 ...
- 156
5
votes
1
answer
638
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 ...
- 5,164
0
votes
0
answers
208
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 ...
- 323
0
votes
1
answer
164
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
...
- 8,619
2
votes
1
answer
202
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 (...
- 121
1
vote
1
answer
295
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 ...
- 311
2
votes
3
answers
1k
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 ...
- 311
2
votes
0
answers
84
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 "...
- 179
3
votes
1
answer
2k
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 ...
- 1
2
votes
1
answer
1k
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 ...
- 123
0
votes
0
answers
631
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 '...
- 961
11
votes
3
answers
3k
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
...
- 1,458
0
votes
1
answer
1k
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(...
- 1,246