check error code in unix
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 of your scripts. The difference between a good 32512 error code unix program and a poor one is often measured in terms of the program's robustness. 255 error code in unix That is, the program's ability to handle situations in which something goes wrong. Exit status As you recall from previous 256 error code unix lessons, every well-written program returns an exit status when it finishes. If a program finishes successfully, the exit status will be zero. If the exit status is anything other than zero, then the
Unix Error Code 16program 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 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 unix error code 137 $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 the exit status of a program. First, you can examine the contents of the $? environment variable. $? will contain the exit status of the last command executed. You can see this work with the following: [me] $ true; echo $? 0 [me] $ false; echo $? 1 The true and false
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 unix error code 24 automation and monitoring projects, a big part of these projects are taking existing scripts and modifying them
Unix Error Code 139to be useful for automation and monitoring tools. One thing I have noticed is sometimes scripts use exit codes and sometimes they don't. It seems
Unix Error Code 2like exit codes are 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 http://linuxcommand.org/wss0150.php a value to their parent process 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 http://bencane.com/2014/09/02/understanding-exit-codes-and-how-to-use-them-in-bash-scripts/ in another script, or wrapped with a bash 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 '
Scripting Unix shell scripting - KSH, CSH, SH, BASH, PERL, PHP, SED, AWK and shell scripts and shell scripting languages here. Search Forums Show Threads Show Posts Tag Search Advanced Search Unanswered Threads Find All Thanked Posts Go to Page... learn linux and unix commands - unix shell scripting http://www.unix.com/shell-programming-and-scripting/42007-error-code-checking.html Error code checking Shell Programming and Scripting Thread Tools Search this https://www.dssw.co.uk/blog/2012-10-08-how-to-add-error-checking-to-your-shell-scripts/ Thread Display Modes
article shows how to add error checking to highlight problems you might otherwise miss. Access the shell on Mac via the Terminal.app Unlike more recently designed languages, shell script does not have an easy answer for error handling. There are no common exception handling routines or ways of wrapping up large blocks of script and asking for errors to fall through to a provided subroutine. Instead shell script asks you, the author, to check individual program exit codes and branch as needed in case of an error. In practice, this means your once short script is going to get a little longer and a little more involved. Unix Exit Status Each program you run through a shell script returns an exit status. This numeric status value tells the calling script if the program completed successfully or if an error was encountered. The exit status is not visible on the command line. This makes it difficult to tell if something went wrong just by looking at the textual output of a shell script. It is possible - even common - for scripts to print nothing and yet encounter multiple errors. Let's consider this simple script: #!/bin/sh cp /Volumes/Documents/criticalfile.txt /Volumes/BackUp/. This script does one thing; it copies a single file from one volume to another using the cp program. Thankfully the cp program is chatty and will print a message if an error is encountered. That is great for us reviewing the output visually, but for the shell running our script the error will go completely unnoticed. This is a problem if our script goes on to do more work, or if we want the script to robustly deal with errors. Let's add error checking to this simple script. #!/bin/sh cp /Volumes/Documents/criticalfile.txt /Volumes/BackUp/. if [ "$?" != "0" ]; then echo "[Error] copy failed!" 1>&2 exit 1 fi We have added an if/fi block below the cp line. The new block checks the special variable $? to see if it equals 0 or not. Unix programs should return 0 if they completed successfully. Any other value means something went wrong. The exact meaning of the returned value is frequently documented in the program's man page. If an error is detected in our script's if/fi block, then a message is printed and the script immediately exits also reporting an error. Why report another error? If our script does not explicitly say exit 1 then the script is assumed to have completed successfully. The error from cp does not matter unless we explicitly make it matter by passing it to our script's caller. William Shotts, Jr's article Er