I want to raise an error in a Bash script with message "Test cases Failed !!!". How to do this in Bash?
For example:
if [ condition ]; then
raise error "Test cases failed !!!"
fi
This depends on where you want the error message be stored.
You can do the following:
echo "Error!" > logfile.log
exit 125
Or the following:
echo "Error!" 1>&2
exit 64
When you raise an exception you stop the program's execution.
You can also use something like exit xxx where xxx is the error code you may want to return to the operating system (from 0 to 255). Here 125 and 64 are just random codes you can exit with. When you need to indicate to the OS that the program stopped abnormally (eg. an error occurred), you need to pass a non-zero exit code to exit.
As #chepner pointed out, you can do exit 1, which will mean an unspecified error.
Basic error handling
If your test case runner returns a non-zero code for failed tests, you can simply write:
test_handler test_case_x; test_result=$?
if ((test_result != 0)); then
printf '%s\n' "Test case x failed" >&2 # write error message to stderr
exit 1 # or exit $test_result
fi
Or even shorter:
if ! test_handler test_case_x; then
printf '%s\n' "Test case x failed" >&2
exit 1
fi
Or the shortest:
test_handler test_case_x || { printf '%s\n' "Test case x failed" >&2; exit 1; }
To exit with test_handler's exit code:
test_handler test_case_x || { ec=$?; printf '%s\n' "Test case x failed" >&2; exit $ec; }
Advanced error handling
If you want to take a more comprehensive approach, you can have an error handler:
exit_if_error() {
local exit_code=$1
shift
[[ $exit_code ]] && # do nothing if no error code passed
((exit_code != 0)) && { # do nothing if error code is 0
printf 'ERROR: %s\n' "$#" >&2 # we can use better logging here
exit "$exit_code" # we could also check to make sure
# error code is numeric when passed
}
}
then invoke it after running your test case:
run_test_case test_case_x
exit_if_error $? "Test case x failed"
or
run_test_case test_case_x || exit_if_error $? "Test case x failed"
The advantages of having an error handler like exit_if_error are:
we can standardize all the error handling logic such as logging, printing a stack trace, notification, doing cleanup etc., in one place
by making the error handler get the error code as an argument, we can spare the caller from the clutter of if blocks that test exit codes for errors
if we have a signal handler (using trap), we can invoke the error handler from there
Error handling and logging library
Here is a complete implementation of error handling and logging:
https://github.com/codeforester/base/blob/master/lib/stdlib.sh
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To add a stack trace to the error handler, you may want to look at this post: Trace of executed programs called by a Bash script
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There are a couple more ways with which you can approach this problem. Assuming one of your requirement is to run a shell script/function containing a few shell commands and check if the script ran successfully and throw errors in case of failures.
The shell commands in generally rely on exit-codes returned to let the shell know if it was successful or failed due to some unexpected events.
So what you want to do falls upon these two categories
exit on error
exit and clean-up on error
Depending on which one you want to do, there are shell options available to use. For the first case, the shell provides an option with set -e and for the second you could do a trap on EXIT
Should I use exit in my script/function?
Using exit generally enhances readability In certain routines, once you know the answer, you want to exit to the calling routine immediately. If the routine is defined in such a way that it doesn’t require any further cleanup once it detects an error, not exiting immediately means that you have to write more code.
So in cases if you need to do clean-up actions on script to make the termination of the script clean, it is preferred to not to use exit.
Should I use set -e for error on exit?
No!
set -e was an attempt to add "automatic error detection" to the shell. Its goal was to cause the shell to abort any time an error occurred, but it comes with a lot of potential pitfalls for example,
The commands that are part of an if test are immune. In the example, if you expect it to break on the test check on the non-existing directory, it wouldn't, it goes through to the else condition
set -e
f() { test -d nosuchdir && echo no dir; }
f
echo survived
Commands in a pipeline other than the last one, are immune. In the example below, because the most recently executed (rightmost) command's exit code is considered ( cat) and it was successful. This could be avoided by setting by the set -o pipefail option but its still a caveat.
set -e
somecommand that fails | cat -
echo survived
Recommended for use - trap on exit
The verdict is if you want to be able to handle an error instead of blindly exiting, instead of using set -e, use a trap on the ERR pseudo signal.
The ERR trap is not to run code when the shell itself exits with a non-zero error code, but when any command run by that shell that is not part of a condition (like in if cmd, or cmd ||) exits with a non-zero exit status.
The general practice is we define an trap handler to provide additional debug information on which line and what cause the exit. Remember the exit code of the last command that caused the ERR signal would still be available at this point.
cleanup() {
exitcode=$?
printf 'error condition hit\n' 1>&2
printf 'exit code returned: %s\n' "$exitcode"
printf 'the command executing at the time of the error was: %s\n' "$BASH_COMMAND"
printf 'command present on line: %d' "${BASH_LINENO[0]}"
# Some more clean up code can be added here before exiting
exit $exitcode
}
and we just use this handler as below on top of the script that is failing
trap cleanup ERR
Putting this together on a simple script that contained false on line 15, the information you would be getting as
error condition hit
exit code returned: 1
the command executing at the time of the error was: false
command present on line: 15
The trap also provides options irrespective of the error to just run the cleanup on shell completion (e.g. your shell script exits), on signal EXIT. You could also trap on multiple signals at the same time. The list of supported signals to trap on can be found on the trap.1p - Linux manual page
Another thing to notice would be to understand that none of the provided methods work if you are dealing with sub-shells are involved in which case, you might need to add your own error handling.
On a sub-shell with set -e wouldn't work. The false is restricted to the sub-shell and never gets propagated to the parent shell. To do the error handling here, add your own logic to do (false) || false
set -e
(false)
echo survived
The same happens with trap also. The logic below wouldn't work for the reasons mentioned above.
trap 'echo error' ERR
(false)
Here's a simple trap that prints the last argument of whatever failed to STDERR, reports the line it failed on, and exits the script with the line number as the exit code. Note these are not always great ideas, but this demonstrates some creative application you could build on.
trap 'echo >&2 "$_ at $LINENO"; exit $LINENO;' ERR
I put that in a script with a loop to test it. I just check for a hit on some random numbers; you might use actual tests. If I need to bail, I call false (which triggers the trap) with the message I want to throw.
For elaborated functionality, have the trap call a processing function. You can always use a case statement on your arg ($_) if you need to do more cleanup, etc. Assign to a var for a little syntactic sugar -
trap 'echo >&2 "$_ at $LINENO"; exit $LINENO;' ERR
throw=false
raise=false
while :
do x=$(( $RANDOM % 10 ))
case "$x" in
0) $throw "DIVISION BY ZERO" ;;
3) $raise "MAGIC NUMBER" ;;
*) echo got $x ;;
esac
done
Sample output:
# bash tst
got 2
got 8
DIVISION BY ZERO at 6
# echo $?
6
Obviously, you could
runTest1 "Test1 fails" # message not used if it succeeds
Lots of room for design improvement.
The draw backs include the fact that false isn't pretty (thus the sugar), and other things tripping the trap might look a little stupid. Still, I like this method.
You have 2 options: Redirect the output of the script to a file, Introduce a log file in the script and
Redirecting output to a file:
Here you assume that the script outputs all necessary info, including warning and error messages. You can then redirect the output to a file of your choice.
./runTests &> output.log
The above command redirects both the standard output and the error output to your log file.
Using this approach you don't have to introduce a log file in the script, and so the logic is a tiny bit easier.
Introduce a log file to the script:
In your script add a log file either by hard coding it:
logFile='./path/to/log/file.log'
or passing it by a parameter:
logFile="${1}" # This assumes the first parameter to the script is the log file
It's a good idea to add the timestamp at the time of execution to the log file at the top of the script:
date '+%Y%-m%d-%H%M%S' >> "${logFile}"
You can then redirect your error messages to the log file
if [ condition ]; then
echo "Test cases failed!!" >> "${logFile}";
fi
This will append the error to the log file and continue execution. If you want to stop execution when critical errors occur, you can exit the script:
if [ condition ]; then
echo "Test cases failed!!" >> "${logFile}";
# Clean up if needed
exit 1;
fi
Note that exit 1 indicates that the program stop execution due to an unspecified error. You can customize this if you like.
Using this approach you can customize your logs and have a different log file for each component of your script.
If you have a relatively small script or want to execute somebody else's script without modifying it to the first approach is more suitable.
If you always want the log file to be at the same location, this is the better option of the 2. Also if you have created a big script with multiple components then you may want to log each part differently and the second approach is your only option.
I often find it useful to write a function to handle error messages so the code is cleaner overall.
# Usage: die [exit_code] [error message]
die() {
local code=$? now=$(date +%T.%N)
if [ "$1" -ge 0 ] 2>/dev/null; then # assume $1 is an error code if numeric
code="$1"
shift
fi
echo "$0: ERROR at ${now%???}${1:+: $*}" >&2
exit $code
}
This takes the error code from the previous command and uses it as the default error code when exiting the whole script. It also notes the time, with microseconds where supported (GNU date's %N is nanoseconds, which we truncate to microseconds later).
If the first option is zero or a positive integer, it becomes the exit code and we remove it from the list of options. We then report the message to standard error, with the name of the script, the word "ERROR", and the time (we use parameter expansion to truncate nanoseconds to microseconds, or for non-GNU times, to truncate e.g. 12:34:56.%N to 12:34:56). A colon and space are added after the word ERROR, but only when there is a provided error message. Finally, we exit the script using the previously determined exit code, triggering any traps as normal.
Some examples (assume the code lives in script.sh):
if [ condition ]; then die 123 "condition not met"; fi
# exit code 123, message "script.sh: ERROR at 14:58:01.234564: condition not met"
$command |grep -q condition || die 1 "'$command' lacked 'condition'"
# exit code 1, "script.sh: ERROR at 14:58:55.825626: 'foo' lacked 'condition'"
$command || die
# exit code comes from command's, message "script.sh: ERROR at 14:59:15.575089"
I am trying to create a linux shell script that compiles a program in java and runs it only if there are no errors from the compiler. This is my attempt, which doesn't work, and runs the program every time even if there are errors:
#!/bin/bash
cd ~/Desktop/Foo/src
compilerOutput=$(javac Foo.java)
if ["$compilerOutput" = ""]; then
java Foo
fi
Like any decent Unix tool, javac should set its exit code to non-zero if there is an error.
javac Foo.java && java Foo
Behind the scenes, the shell examines the exit code (which is available as $? if you want to examine it explicitly) and takes the next action only if it is zero.
If you want more complex logic, you can say
if javac Foo.java; then
date +"%c success" >>logfile.log
java Foo
else
date +"%c fail (exit code $?)" >>logfile.log
echo "Oh dear" | wall
fi
The root cause of problem is
compilerOutput=$(javac Foo.java)
When you use command substitution, only the standard output get assigned to compilerOutput
For javac there is no standard output, that is the standard output is always empty, What you see on the screen in standard error
There for even when there is no errors in the program or not
if ["$compilerOutput" = ""]; then
will always be true as the standard output is always empty
Solution
The proper way of doing this is to get the exit status of the previous command through the shell variable $?
Code
#!/bin/bash
cd ~/Desktop/Foo/src
javac Foo.java 2> errors
if [ $? = "0" ]; then
java Foo
fi
Changes made
javac Foo.java 2> errors
This statement redirects bstandard error to errors file
if [ $? = "0" ]; then
Checks if the exit status of previous command, javac Foo.java is 0 (Successfull compilation)
I'm writing a script to test a program and I'm getting caught at this portion
if (("$x"==22)); then
echo "Checking for whether wrong input file is detected."
if diff ${arr[$x]} <(./compare ); then
echo Output is as expected.
else
echo Output is not as expected. Check for errors.
fi
else
if diff -q ${arr[$x]} <(./compare $i); then
echo Output is as expected.
else
echo Output is not as expected. Check for errors.
fi
fi
So what it's doing is testing my program against known output. However, for the case where I use ./compare without an argument, I want to receive an error message from my program specifying that the argument is missing. The test file it's using, "22" let's call it result22.txt, has the exact same output my program would give from just running ./compare (no arguments). However, when I run it using the script, it says that result22.txt differs from just running ./compare. I'm pretty sure I"m running the script wrong, any ideas?
Additionaly information, i is a known input test file that's from an array, x is an incremental variable to count which loop we're on. So arr[$x] is just accessing the nth file from the known output files.
Compare is my own compare program to run.
I am getting a non-deterministic crash in a library I am using which occurs a lot less frequently when the library's full debugging is turned on. I want to run it repeatedly until the program crashes, and then look at the detailed debug (let's assume that unit-test-command with args calls the code I am interested in)
This is the code I have in my script:
#!/bin/bash
while [[ $(unit-test-command with args) == 0 ]]
do
echo ""
done
However, not only does it only go through the loop once irrespective of the return value of the command (which is non-zero when it crashes), but it also only displays the output of my program, and not the output of the library debugging.
What I am doing wrong?
$(command) expands to the console output, not to return code. For example, uname returns 0 and $(uname) returns "linux".
Try so:
while unit-test-command with args ; do : ; done
#!/bin/bash
while [ true ];do
unit-test-command with args
if [ $? != 0 ];then
echo "failed"
break
fi
echo "didn't faile
sleep 10
done
I'm debugging someone else's code, and I've run into a situation I wouldn't know how to produce if I tried to code it deliberately. It's coming from a very large Bash script, being run by Bash 4.1.2 on a CentOS 6 box. While the overall program is gigantic, the error consistently occurs in the following function:
get_las() {
echo "Getting LAS..."
pushd ${ferret_workdir} >& /dev/null
#Download:
if [ ! -e ${las_dist_file} ] || ((force_install)) ; then
echo "Don't see LAS tar file ${las_dist_file}"
echo "Downloading LAS from ${las_dist_file} -to-> $(pwd)/${las_dist_file}"
echo "wget -O '${las_dist_file}' '${las_tar_url}'"
wget -O "${las_dist_file}" "${las_tar_url}"
[ $? != 0 ] && echo " ERROR: Could not download LAS:${las_dist_file}" && popd >/dev/null && checked_done 1
fi
popd >& /dev/null
return 0
}
If I allow the script to run from scratch in a pristine environment, when this section is reached it will spit out the following error and die:
Don't see LAS tar file las-esg-v7.3.9.tar.gz
Downloading LAS from las-esg-v7.3.9.tar.gz -to-> /usr/local/src/esgf/workbench/esg/ferret/7.3.9/las-esg-v7.3.9.tar.gz
wget -O 'las-esg-v7.3.9.tar.gz' 'ftp://ftp.pmel.noaa.gov/pub/las/las-esg-v7.3.9.tar.gz'
/usr/local/bin/esg-product-server: line 428: /usr/bin/wget: Argument list too long
ERROR: Could not download LAS:las-esg-v7.3.9.tar.gz
Note that I even have a debug echo in there to prove that the arguments are only two small strings.
If I let the program error out at the point above and then immediately re-run it from the same expect script, with the only change being that it has already completed all the stages prior to this one and is detecting that and skipping them, this section will execute normally with no error. This behavior is 100% reproducible on my test box -- if I purge all traces that running the code leaves, the first run thereafter bombs out at this point, and subsequent runs will be fine.
The only thing I can think is that I've run into some obscure bug in Bash itself that is somehow causing it to leak MAX_ARG_PAGES memory invisibly, but I can't think of even any theoretical ways to make this happen, so I'm asking here.
What the heck is going on and how do I make it stop (without extreme measures like recompiling the kernel to just throw more memory at it)?
Update: To answer a question in the comments, line 428 is
wget -O "${las_dist_file}" "${las_tar_url}"
The error E2BIG refers to the sum of the bytes in the environment and the argv list. Has the script exported a huge number (or huge size) of variables? Run printenv right before the wget to see what's going on.