I try to exit from the my javascript code like this:
slimer.exit(1);
But I don't get the 1 exit code. I try even:
slimer.exit(2);
I get exit code 0 forever.
Any idea/help?
Straight from the documentation... (emphasis mine)
exit()
It stops the script and SlimerJS exit.
It accepts an optional exit code but it is ignored because of a
limitation in Firefox/XulRunner.
slimer.exit();
The exit code is ignored. This is a known issue in slimerJS.
Related
I know $? from shell holds the last executed programs exit status.
For example, when I run below commands, I saw different status for different situation.
test$ hello
-bash: hello: command not found
test$ echo $?
127
test$ expr 1 / 0
expr: division by zero
test$ echo $?
2
I was wondering if there is any common exit status list in system or internet where i can get all the exit status with their descriptions. I found a list here, but some codes are missing, for example status code 127.
There can be no comprehensive list, because the meaning of command exit statuses is inherently command-specific. For a given command, you can usually get information about this on the respective command's manual page and Info documents.
In the case of
test$ hello
-bash: hello: command not found
test$ echo $?
127
the exit code 127 comes from bash, because the requested command itself couldn't be found.
In the case of
test$ expr 1 / 0
expr: division by zero
test$ echo $?
2
the exit code 2 comes from expr.
Some of these commands might be standardized or at least coordinated for several commands or a group of commands (e.g. "sh-compatible shells", I could imagine), but unless a command wants to conform to one of these conventions (and there are probably multiple conflicting conventions around), the command's authors are completely free to decide what they want their exit status codes to mean.
There's one important exception: All UNIX commands should adhere to this loose rule to be good citizens and provide meaningful composability (e.g. with pipes) on the command line:
0 means 'success' or "true"/"truthy"
non-0 means (in a very broad sense) 'failure' or 'non-success' or "false"/"falsy"
As you can see, this still leaves a lot of room for interpretation, which is perfectly intended, because these meanings must be specific to the context of the individual commands. (Consider e.g. the false command, that has the very purpose to "fail", thus always returns a non-0 exit code.)
The list you found describes return codes for system calls. System calls are when a program makes a request (in)to the kernel and are not the same as command invocation, thus these return codes are not (necessarily) the same as command exit codes.
The exit status is a numeric value that is returned by a program to the calling program or shell. In C programs, this is represented by the return value of the main() function or the value you give to exit(3). The only part of the number that matters are the least significant 8 bits, which means there are only values from 0 to 255.
Code Description
0 success
1-255 failure (in general)
126 the requested command (file) can't be executed (but was found)
127 command (file) not found
128 according to ABS it's used to report an invalid argument to the exit
builtin, but I wasn't able to verify that in the source code of Bash
(see code 255)
128 + N the shell was terminated by the signal N (also used like this by
various other programs)
255 wrong argument to the exit builtin (see code 128)
The lower codes 0 to 125 are not reserved and may be used for whatever the program likes to report. A value of 0 means successful termination, a value not 0 means unsuccessful termination. This behaviour (== 0, != 0) is also what Bash reacts on in some code flow control statements like if or while.
The above excerpt taken from Exit Status section from Bash Hackers Wiki.
The list you showed is really the closest possible thing to a "standardization", but frankly it looks more legit than it actually is. As far as I am aware of, almost no one pays much attention to these guys, but instead everyone names their own exit statuses:
Execute test1.sh
#!/bin/bash
a=10 ; [ "$a" -eq 9 ] && echo "Cool!" || exit 200
Output:
:~$ test1.sh
:~$ echo $?
200
I want to raise an error in a Bash script with message "Test cases Failed !!!". How to do this in Bash?
For example:
if [ condition ]; then
raise error "Test cases failed !!!"
fi
This depends on where you want the error message be stored.
You can do the following:
echo "Error!" > logfile.log
exit 125
Or the following:
echo "Error!" 1>&2
exit 64
When you raise an exception you stop the program's execution.
You can also use something like exit xxx where xxx is the error code you may want to return to the operating system (from 0 to 255). Here 125 and 64 are just random codes you can exit with. When you need to indicate to the OS that the program stopped abnormally (eg. an error occurred), you need to pass a non-zero exit code to exit.
As #chepner pointed out, you can do exit 1, which will mean an unspecified error.
Basic error handling
If your test case runner returns a non-zero code for failed tests, you can simply write:
test_handler test_case_x; test_result=$?
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
Related posts
Error handling in Bash
The 'caller' builtin command on Bash Hackers Wiki
Are there any standard exit status codes in Linux?
BashFAQ/105 - Why doesn't set -e (or set -o errexit, or trap ERR) do what I expected?
Equivalent of __FILE__, __LINE__ in Bash
Is there a TRY CATCH command in Bash
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
Ignoring specific errors in a shell script
Catching error codes in a shell pipe
How do I manage log verbosity inside a shell script?
How to log function name and line number in Bash?
Is double square brackets [[ ]] preferable over single square brackets [ ] in Bash?
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"
When I am giving exit command in Groovysh command prompt I am getting following error. Other commands are working fine.
Groovy Shell (2.3.6, JVM: 1.8.0_25)
...
groovy:000> exit
Unknown property: exit
groovy:000>
I tried with Ctrl + D and it is also working fine.
exit was replaced with :exit, but unfortunately I don't remember in which version it was introduced.
EDIT
I've found it. See this tweet.
As per this page, http://groovy-lang.org/groovysh.html (See 1.4.1. Recognized Commands), the ONLY way to exit the shell is by pressing :x or :exit.
You can also do so by doing Ctrl + C, however it will give a warning of an abnormal termination of JVM.
I've seen a lot of strange quirks in CentOS 6.5's init.d scripts, but one pattern I've seen at the end of most of these scripts is
case "$1" in
# ... commands here
esac
exit $?
What is the purpose of "exit $?" here?
It makes the script return the return code of the last significant command to the calling init system. Whenever a command exits, its return code is stored on $? by the shell.
It's actually not really necessary to explicitly specify $? but scripters probably just include it to be clear about what it intends to do.
exit: exit [n]
Exit the shell.
Exits the shell with a status of N. If N is omitted, the exit status
is that of the last command executed.
I also hope you don't actually mean eend $? of OpenRC:
eend retval [string ]
If retval does not equal 0 then output the string using eerror and !! in square > brackets at the end of the line. Otherwise output ok in square brackets at the end of the line. The value of retval is returned.
See source.
This question already has answers here:
Are there any standard exit status codes in Linux?
(11 answers)
Closed 9 years ago.
I understand that EXIT command causes the shell or program to terminate.
But what is the difference between the below:
exit 2
exit 3
exit 4
exit $?
how is exit 2 different from exit 3 and so on
This is only an exit code. 0 is for fine exit, otherwise it's the error code. $? is a shell variable storing the previous exit value (so the program which ran before your one).
The exit command takes a single value which is the value of the process (e.g. shell) return code. $? is the return code from the last command executed by the shell.
For instance, the script which exits with a return code corresponding to the first argument:
#!/bin/sh
exit $1
Would give you:
# ./script 1
# echo $?
1
# ./script 2
# echo $?
2
Note on most UNIX systems, the return code is limited to a numeric value between 0 and 255, with 0 indicates success and 1-255 providing error information (specific to each process).
From the Advanced Bash-Scripting Guide, Chapter 6: Exit and Exit Status:
The exit command terminates a script, just as in a C program. It can also return a value, which is available to the script's parent process.
So the exit command lets you assign your own exit value, which you could describe in its man page, for example.
The $? will return the exit code of the previous command. For example; You write a script that executes cat example.txt, which results exit code 1. If you then do exit $?, your script will exit with the same code as cat example.txt
More info on exit codes here: Advanced Bash-Scripting Guide Chapter 6: Exit and Exit Status
Some info on $? here: What is the $? variable in shell scripting?