Exit Error Codes In Unix
Contents |
>ExampleComments1Catchall for general errorslet "var1 = 1/0"Miscellaneous errors, such as "divide
Linux Exit Codes
by zero" and other impermissible operations2Misuse of shell builtins (according to Bash documentation)empty_function() {}Missing keyword or command, or
Exit Code Python
permission problem (and diff return code on a failed binary file comparison).126Command invoked cannot execute/dev/nullPermission problem or command exit code 1 is not an executable127"command not found"illegal_commandPossible problem with $PATH or a typo128Invalid argument to exitexit 3.14159exit takes only integer args in the range 0 - 255 (see first footnote)128+nFatal error signal "n"kill -9 $PPID of script$? returns 137 (128 + 9)130Script terminated by Control-CCtl-CControl-C is fatal error signal 2, (130 = 128 + 2, see above)255*Exit status out of rangeexit -1exit takes only integer args in the range 0 - 255
exit codes, exit codes are important and this article describes how to use them in your scripts and understand them in general. Written by Benjamin Cane on 2014-09-02 14:45:00| 4 min read Sponsored by Lately I've been working on a lot of automation and monitoring
Bash Script Exit On Error
projects, a big part of these projects are taking existing scripts and modifying them to be useful exit bash shell for automation and monitoring tools. One thing I have noticed is sometimes scripts use exit codes and sometimes they don't. It seems like exit codes are
Exit Codes Windows
easy for poeple to forget, but they are an incredibly important part of any script. Especially if that script is used for the command line. What are exit codes? On Unix and Linux systems, programs can pass a value to their parent process http://tldp.org/LDP/abs/html/exitcodes.html while terminating. This value is referred to as an exit code or exit status. On POSIX systems the standard convention is for the program to pass 0 for successful executions and 1 or higher for failed executions. Why is this important? If you look at exit codes in the context of scripts written to be used for the command line the answer is very simple. Any script that is useful in some fashion will inevitably be either used in another script, or wrapped with a bash http://bencane.com/2014/09/02/understanding-exit-codes-and-how-to-use-them-in-bash-scripts/ one liner. This becomes especially true if the script is used with automation tools like SaltStack or monitoring tools like Nagios, these programs will execute scripts and check the status code to determine whether that script was successful or not. On top of those reasons, exit codes exist within your scripts even if you don't define them. By not defining proper exit codes you could be falsely reporting successful executions which can cause issues depending on what the script does. What happens if I don't specify an exit code In Linux any script run from the command line has an exit code. With Bash scripts, if the exit code is not specified in the script itself the exit code used will be the exit code of the last command run. To help explain exit codes a little better we are going to use a quick sample script. Sample Script: #!/bin/bash touch /root/test echo created file The above sample script will execute both the touch command and the echo command. When we execute this script (as a non-root user) the touch command will fail, ideally since the touch command failed we would want the exit code of the script to indicate failure with an appropriate exit code. To check the exit code we can simply print the $? special variable in bash. This variable will print the exit code of the last run command. Execution: $ ./tmp.sh touch: cannot touch '/root/test': Permission denied created file $ echo $? 0 As you can see after running the ./tmp.s
and Signals and Traps (Oh My!) - Part 1 by William Shotts, Jr. In this lesson, we're going to look at handling errors during the execution http://linuxcommand.org/wss0150.php of your scripts. The difference between a good program and a poor one is often measured in terms of the program's robustness. That is, the program's ability to handle http://www.linuxjournal.com/article/10844 situations in which something goes wrong. Exit status As you recall from previous lessons, every well-written program returns an exit status when it finishes. If a program finishes exit code successfully, the exit status will be zero. If the exit status is anything other than zero, then the program failed in some way. It is very important to check the exit status of programs you call in your scripts. It is also important that your scripts return a meaningful exit status when they finish. I once had a linux exit code Unix system administrator who wrote a script for a production system containing the following 2 lines of code: # Example of a really bad idea cd $some_directory rm * Why is this such a bad way of doing it? It's not, if nothing goes wrong. The two lines change the working directory to the name contained in $some_directory and delete the files in that directory. That's the intended behavior. But what happens if the directory named in $some_directory doesn't exist? In that case, the cd command will fail and the script executes the rm command on the current working directory. Not the intended behavior! By the way, my hapless system administrator's script suffered this very failure and it destroyed a large portion of an important production system. Don't let this happen to you! The problem with the script was that it did not check the exit status of the cd command before proceeding with the rm command. Checking the exit status There are several ways you can get and respond to
are for—letting you know when things went wrong. Last month, we looked at signals, the rudimentary mechanism that processes on a Linux box can use to communicate events and state changes. We talked about how each of the signals can be sent manually to a running process with the kill command, and how shell scripts then can catch and respond to specific signals (though not all of them—some cannot be caught because they're actually handled by the operating system itself). Analogous to signals, exit codes turn out to be an easy way for processes to communicate state back to the calling parent process, in a way that most Linux users just ignore. Not anymore—this month, we're going to take a closer look. mv Exit Codes Let's start with a simple Linux command that everyone's probably already mastered: mv, which moves a file or directory from one spot in the filesystem to another (and/or renames it). As you know, you can generate errors if the target is missing, destination is missing and so on. Here's quick example: $ mv missing ~/missing2 mv: cannot move `missing' to `.../missing2': No such file or directory You see an error; obviously, it didn't work. Ah, but behind the scenes, a numeric “return code” variable has been set in the shell too, something you can test and respond to within a shell script. Check out this sequence: $ echo $? 0 $ mv missing ~/missing2 mv: cannot move `missing' to `.../missing2': No such file or directory $ echo $? 1 $ echo test me test me $ echo $? 0 If no error occurs when executing a command, the exit code (which we reference in the shell with the shorthand $?) will have the value of 0: no error. Now, if I run a command that fails, the exit code will have a nonzero value. In the case of the failing mv command above, the error code w