From a bash script I want to run a command which might fail, store its exit code in a variable, and run a subsequent command regardless of that exit code.
Examples of what I'm trying to avoid:
Using set:
set +e # disable exit on error (it was explicitly enabled earlier)
docker exec $CONTAINER_NAME npm test
test_exit_code=$? # remember exit code of previous command
set -e # enable exit on error
echo "copying unit test result file to host"
docker cp $CONTAINER_NAME:/home/test/test-results.xml .
exit $test_exit_code
Using if:
if docker exec $CONTAINER_NAME npm test ; then
test_exit_code=$?
else
test_exit_code=$?
fi
echo "copying unit test result file to host"
docker cp $CONTAINER_NAME:/home/test/test-results.xml .
exit $test_exit_code
Is there a semantically straightforward way to tell bash "run command without exiting on error, and tell me its exit code"?
The best alternative I have is still confusing and requires comments to explain to subsequent developers (it's just a terser if/else):
docker exec $CONTAINER_NAME npm test && test_exit_code=$? || test_exit_code=$?
echo "copying unit test result file to host"
docker cp $CONTAINER_NAME:/home/test/test-results.xml .
exit $test_exit_code
I believe you could just use the || operator? Which is equivalent to an "if − else" command.
Would the following address your use case? (otherwise feel free to comment!)
set -e # implied in a CI context
exit_status=0
docker exec "$CONTAINER_NAME" npm test || exit_status=$?
docker cp "$CONTAINER_NAME:/home/test/test-results.xml" .
exit "$exit_status"
or more briefly:
set -e # implied in a CI context
docker exec "$CONTAINER_NAME" npm test || exit_status=$?
docker cp "$CONTAINER_NAME:/home/test/test-results.xml" .
exit "${exit_status:-0}"
As an aside, if you are not interested in this exit status code, you can also do something like this:
set -e # implied in a CI context
docker exec "$CONTAINER_NAME" npm test || :
docker cp "$CONTAINER_NAME:/home/test/test-results.xml" .
For more details on the || : tip, see e.g. this answer on Unix-&-Linux SE:
Which is more idiomatic in a bash script: || true or || :?
Very simply save the return-code if command failed:
#!/usr/bin/env sh
# Implied by CI
set -e
# Initialise exit return code
rc=0
# Run command or save its error return code if it fail
docker exec "$CONTAINER_NAME" npm test || rc="$?"
printf '%s\n' "copying unit test result file to host"
# Run other command regardless if first one failed
docker cp "$CONTAINER_NAME:/home/test/test-results.xml" .
# Exit with the return code of the first command
exit "$rc"
You could use a kind of try catch, to get the exit code and use a simple switch case to run another commands depending on the error exit code:
(
exit 2
#here your command which might fail
)
exit_code=$?
case "$exit_code" in
0) echo "Success execution"
#do something
;;
1) echo "Error type 1"
#do something
;;
2) echo "Error type 2"
#do something
;;
*) echo "Unknown error type: $exit_code"
;;
esac
Related
I have a Bash shell script that invokes a number of commands.
I would like to have the shell script automatically exit with a return value of 1 if any of the commands return a non-zero value.
Is this possible without explicitly checking the result of each command?
For example,
dosomething1
if [[ $? -ne 0 ]]; then
exit 1
fi
dosomething2
if [[ $? -ne 0 ]]; then
exit 1
fi
Add this to the beginning of the script:
set -e
This will cause the shell to exit immediately if a simple command exits with a nonzero exit value. A simple command is any command not part of an if, while, or until test, or part of an && or || list.
See the bash manual on the "set" internal command for more details.
It's really annoying to have a script stubbornly continue when something fails in the middle and breaks assumptions for the rest of the script. I personally start almost all portable shell scripts with set -e.
If I'm working with bash specifically, I'll start with
set -Eeuo pipefail
This covers more error handling in a similar fashion. I consider these as sane defaults for new bash programs. Refer to the bash manual for more information on what these options do.
To add to the accepted answer:
Bear in mind that set -e sometimes is not enough, specially if you have pipes.
For example, suppose you have this script
#!/bin/bash
set -e
./configure > configure.log
make
... which works as expected: an error in configure aborts the execution.
Tomorrow you make a seemingly trivial change:
#!/bin/bash
set -e
./configure | tee configure.log
make
... and now it does not work. This is explained here, and a workaround (Bash only) is provided:
#!/bin/bash
set -e
set -o pipefail
./configure | tee configure.log
make
The if statements in your example are unnecessary. Just do it like this:
dosomething1 || exit 1
If you take Ville Laurikari's advice and use set -e then for some commands you may need to use this:
dosomething || true
The || true will make the command pipeline have a true return value even if the command fails so the the -e option will not kill the script.
If you have cleanup you need to do on exit, you can also use 'trap' with the pseudo-signal ERR. This works the same way as trapping INT or any other signal; bash throws ERR if any command exits with a nonzero value:
# Create the trap with
# trap COMMAND SIGNAME [SIGNAME2 SIGNAME3...]
trap "rm -f /tmp/$MYTMPFILE; exit 1" ERR INT TERM
command1
command2
command3
# Partially turn off the trap.
trap - ERR
# Now a control-C will still cause cleanup, but
# a nonzero exit code won't:
ps aux | grep blahblahblah
Or, especially if you're using "set -e", you could trap EXIT; your trap will then be executed when the script exits for any reason, including a normal end, interrupts, an exit caused by the -e option, etc.
The $? variable is rarely needed. The pseudo-idiom command; if [ $? -eq 0 ]; then X; fi should always be written as if command; then X; fi.
The cases where $? is required is when it needs to be checked against multiple values:
command
case $? in
(0) X;;
(1) Y;;
(2) Z;;
esac
or when $? needs to be reused or otherwise manipulated:
if command; then
echo "command successful" >&2
else
ret=$?
echo "command failed with exit code $ret" >&2
exit $ret
fi
Run it with -e or set -e at the top.
Also look at set -u.
On error, the below script will print a RED error message and exit.
Put this at the top of your bash script:
# BASH error handling:
# exit on command failure
set -e
# keep track of the last executed command
trap 'LAST_COMMAND=$CURRENT_COMMAND; CURRENT_COMMAND=$BASH_COMMAND' DEBUG
# on error: print the failed command
trap 'ERROR_CODE=$?; FAILED_COMMAND=$LAST_COMMAND; tput setaf 1; echo "ERROR: command \"$FAILED_COMMAND\" failed with exit code $ERROR_CODE"; put sgr0;' ERR INT TERM
An expression like
dosomething1 && dosomething2 && dosomething3
will stop processing when one of the commands returns with a non-zero value. For example, the following command will never print "done":
cat nosuchfile && echo "done"
echo $?
1
#!/bin/bash -e
should suffice.
I am just throwing in another one for reference since there was an additional question to Mark Edgars input and here is an additional example and touches on the topic overall:
[[ `cmd` ]] && echo success_else_silence
Which is the same as cmd || exit errcode as someone showed.
For example, I want to make sure a partition is unmounted if mounted:
[[ `mount | grep /dev/sda1` ]] && umount /dev/sda1
I have a docker container that runs a script via the entrypoint directive. The container closes after the entrypoint script is finished. I need to get the exit code from the script in order to do some logging if the script fails. Right now I'm thinking of something like this
docker run container/myContainer:latest
if [ $? != 0 ];
then
do some stuff
fi
Is this proper way to achieve this? Specifically, will this be the exit code of docker run or of my entrypoint script?
Yes, the docker container run exit code is the exit code from your entrypoint/cmd:
$ docker container run busybox /bin/sh -c "exit 5"
$ echo $?
5
You may also inspect the state of an exited container:
$ docker container inspect --format '{{.State.ExitCode}}' \
$(docker container ls -lq)
5
Checking the value of $? is not needed if you just want to act upon the exit status of the previous command.
if docker run container/myContainer:latest; then
do_stuff
fi
The above example will run/execute do_stuff if the exit status of docker run is zero which is a success.
You can add an else and elif clause in that
Or if you want to negate the exit status of the command.
if ! docker run container/myContainer:latest; then
do_stuff
fi
The above example will run do_stuff if the exit status of docker run is anything but zero, e.g. 1 and going up, since the ! negates.
If the command has some output and if does not have a silent/quite flag/option you can redirect it to /dev/null
if docker run container/myContainer:latest >/dev/null; then
do_stuff
fi
Should not output anything to stdout
see help test | grep -- '^[[:blank:]]*!'
In some cases if some output is still showing then that might be stderr which you can silent with >/dev/null 2>&1 instead of just >/dev/null
I have shell file (deploy.sh) do the following commands:
npm run build:prod
docker-compose -f .docker/docker-compose.ecr.yml build my-app
docker-compose -f .docker/docker-compose.ecr.yml push my-app
aws ecs update-service --cluster ...
I want to stop the execution of the bash when error occurred from one of the commands.
Which command does that in shell?
If you want to test the success or failure of a command, you can rely on its exit code. Knowing that each command will return a 0 on success or any other number on failure, you have a few options on how to handle each command's errors.
|| handler
npm run build:prod || exit 1
if condition
if docker-compose -f .docker/docker-compose.ecr.yml build my-app; then
printf "success\n"
else
printf "failure\n"
exit 1
fi
the $? variable
docker-compose -f .docker/docker-compose.ecr.yml push my-app
if [ $? -gt 0 ]; then
printf "Failure\n"
exit 1
fi
traps
err_report() {
echo "Error on line $1"
}
trap 'err_report $LINENO' ERR
aws ecs update-service --cluster ...
set -e
To globally "exit on error", then set -e will do just that. It won't give you much info, but it'll get the job done.
You can use set -e to exit on errors. And even better, you can set -e and use a trap function.
#!/bin/bash
set -e
trap 'catch $? $LINENO' EXIT
catch() {
echo "catching!"
if [ "$1" != "0" ]; then
# error handling goes here
echo "Error $1 occurred on $2"
fi
}
npm run build:prod
docker-compose -f .docker/docker-compose.ecr.yml build my-app
docker-compose -f .docker/docker-compose.ecr.yml push my-app
aws ecs update-service --cluster ...
source: https://medium.com/#dirk.avery/the-bash-trap-trap-ce6083f36700
Did a fast search on Google and it seems there isnt. Best is to use && or || or if ... else blocks see links below:
SO-Try Catch in bash
and
Linuxhint
Hope this helps
So I have this at the start of a bash script file (-e and -o).
However, in some functions, I would like for it to not exit out. Example
set -e
set -o pipefail
function check_status {
echo "Start Check"
docker exec mservice bash -c "echo 'Hello' | grep 'fail'"
echo "End check"
}
check_status
How can I prevent this from exiting out of the script - basically if I run this, it would printout "Start Check", but then exit because the next command returns a '1'.
I would like to be able to disable and enable the set -e/-o in multiple places or in different functions.
For all options, the opposite of set -𝓧 is set +𝓧 (note the plus sign).
So set +e will undo set -e, and set +o pipefail will undo set -o pipefail.
You can also leave the settings alone, and do something as simple as:
docker exec mservice bash -c "echo 'Hello' | grep 'fail'" || true
...and in so doing force a successful run of that command list. There would be no programmatic way to detect the failure of the docker command in this case, but if the command emits some error message, the human observer may notice.
Or you can handle the error in your function
#!/usr/bin/env bash
set -e
set -o pipefail
function check_status {
if docker exec mservice bash -c "echo 'Hello' | grep 'fail'"; then
echo good
else
echo bad
fi
}
status=$(check_status)
if [ "$status" = 'bad' ]; then
echo "check_status failed, but still running, handling the error..."
fi
Saving as testfail.sh and running it for me causes failure, since my docker installation does not include anything named mservice:
$ ./testfail.sh
Error response from daemon: No such container: mservice
check_status failed, but still running, handling the error...
$
My bash script (init.sh) call another script (script.sh) and I want to test the error code from script.sh before doing any further action in init.sh.
I thought about testing it with $?, but it does not work
My init.sh is like the following:
#!/bin/bash
set -e
echo "Before call"
docker run -v $PWD:/t -w /t [command]
if [ $? == 1 ]; then
echo "Issue"
fi
echo "After call"
I only got the Before call from stdout and not the After call.
I know for a fact that if I execute docker run -v $PWD:/t -w /t [command] alone with wrong arguments, then echo $? will rightly display 1.
I was thinking that I do not catch the exit code from scrip.sh, but from somewhere else.
Any ideas?
You running the script with set -e. This means that if any command exits with a non zero status, bash will stop executing all subsequent lines. So here, if docker exits with status 1, the conditional that follows will not have a chance to run at all. Try this instead:
#!/bin/bash
set -e
echo "Before call"
if ! docker run -v $PWD:/t -w /t [command]; then
echo "Issue"
fi
echo "After call"
This runs the command inside the if test which suppresses the effect of set -e I described above and gives you a chance to catch the error. Note this is will also catch all non-zero statuses, not just 1.
Bash numeric comparison operator is -eq, and not ==...
So:
#!/bin/bash
set -e
echo "Before call"
docker run -v $PWD:/t -w /t [command]
if [ $? -eq 1 ]; then
echo "Issue"
fi
echo "After call"
set -e is generally a bad idea. Sure, it may seem like a good idea to have your script exit automatically in the event of an unexpected error, but the problem is that set -e and you may have different ideas about what constitutes a fatal error.
Instead, do your own error handling.
#!/bin/bash
echo "Before call"
docker run -v $PWD:/t -w /t [command]
docker_status=$?
if [ $docker_status != 0 ]; then
echo "docker returned: $docker_status"
exit $docker_status
fi
echo "After call"
In this simple code, I've somewhat redundantly saved the value of $? to another variable first. This ensures that it is preserved after you start executing other commands that examine, log, or otherwise process the value of $?. Also, I'm logging and exiting here on any non-zero status, not just 1. In theory, you might take different action for an exit status of 1 than for an exit status of 2, but here we take the same log-then-exit action for any error.