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Bash Script Error Checking


You can use command || true, or if you have a longer section of code, you can turn off the error checking, but I recommend you use this sparingly. See also stackoverflow.com/questions/673055/… –Charles Duffy Jun 9 '11 at 3:25 before you break it again, test your change. If you read the Letters section in Linux Journal, you know I haven't covered this topic because, well, you have covered it for me! If EXPRESSION is a single argument, ‘test’ returns false if the argument is null and true otherwise." –Lekensteyn Mar 25 at 18:31 | show 3 more comments up vote 37 down this contact form

And now, finally, the completed script code, as any decent script writer should be propably doing it using some pre-action checking as well. #!/bin/bash # trap handler: print location of last Unix Exit Status Each program you run through a shell script returns an exit status. Why don't most major game engines use gifs for animated textures? It contains the current # line number.

Bash Quit On Error

So, something like; cd /nonexistant if [ $? -ne 0 ] then echo failed else echo success! Conventions are a good thing, but they're secondary to functioning code. –Draemon Jun 9 '11 at 21:10 2 @Draemon, I actually disagree. Sequence Different shells have different return status indicators (the C shell, for example, uses $status), but the most basic is Bash/the Bourne shell, which is what we've focused on since I Login to save this as favorite Subscribe Blogs Reviews HOWTOs Geek Guides Hep & Tips How to Get Linux Getting Help Loading Trending Topics SysAdmin DevOps Security Cloud HPC Mobile Virtualization

cp -a /var/www /var/www-tmp for file in $(find /var/www-tmp -type f -name "*.html"); do perl -pi -e 's/www.example.net/www.example.com/' $file done mv /var/www /var/www-old mv /var/www-tmp /var/www This means that if there What to tell to a rejected candidate? What do you think about that method? –skozin Jan 11 at 16:36 @sam.kozin I don't have time to review your answer in detail, it looks good on principle. Bash Script Error Command Not Found The second use, ${1:-"Unknown Error"} means that if parameter 1 ($1) is undefined, substitute the string "Unknown Error" in its place.

rm -rf $chroot/usr/share/doc If you ran the script above and accidentally forgot to give a parameter, you would have just deleted all of your system documentation rather than making a smaller Exception Handling Shell Script Adopt A Jet/Book Integral using residue theorem complex analysis What could cause the throttle to stick in my Ford Ranger? So in general I call programs in an "if !" type statement. The name of the missing function (or executable) will be passed in $_ function handle_error { status=$?

In the end, the trap handler could be setup to send and email using both information from the intercepted trap and the logfile. Bash Script Error Output Let's assume a script, which is trying to delete a directory. It should work in all POSIX-compatible shells if you remove local keywords, i.e. These commands have been designed so that they WILL fail for the sake of documentary purposes. #!/bin/bash # trap handler: print location of last error and process it further # function

Exception Handling Shell Script

chroot=$1 ... It is very important to check the exit status of programs you call in your scripts. Bash Quit On Error First, you can examine the contents of the $? Bash Script Error Code Intuition behind Harmonic Analysis in Analytic Number Theory A simple visual puzzle to die for Does mean=mode imply a symmetric distribution?

Browse other questions tagged bash shell shell-script error-handling or ask your own question. weblink The traps catch the common terminating signals and make sure everything gets cleaned up. For example, false | true will be considered to have succeeded. Another disadvantage of using traps is bad composability, as you risk overwriting previous trap that might be set earlier up in the caller chain. Bash Script Check Error Status

To demonstrate how accurately the trap handler works, I added some further commands. In this case you'd want the user to not exist and all their files to be removed. Aborting" rm * If an exit is not required in case of error, then you can even do this: # Another way to do it if exiting is not desired cd http://waspsoft.com/bash-script/bash-shell-error-checking.html you should create a github project for it, so people can easily make improvements and contribute back.

echo "Example of error with line number and message" error_exit "$LINENO: An error has occurred." Do you have a better error handling routine that you use in BASH scripts? Bash Script Error Log Didn't know about Code Review. –skozin Jan 11 at 17:27 add a comment| up vote 2 down vote To expand on the @Gilles' answer: Indeed, set -e doesn't work inside commands Activate Hearthstone season chest cards?

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  • share|improve this answer edited Oct 22 '13 at 12:52 Stéphane Chazelas 175k28281504 answered Oct 22 '13 at 12:39 JRFerguson 5,60811522 @Stephane Chazelas point of quoting and signaling end-of-options well
  • You can read more about parameter expansion in the bash man page under the topic "EXPANSIONS".
  • test.sh: line 34: rmdiir: command not found test.sh: line 45: exit status of last command: 127 failed: directory not deleted.
  • Bad-practices but mostly-working code lives forever (and gets propagated). –Charles Duffy May 22 '14 at 16:55 but you didn't notice.
  • Using -e gives you error checking for free.
  • For example, when you create a directory, if the parent directory doesn't exist, mkdir will return an error.

up vote 5 down vote favorite 1 I made the following script: # !/bin/bash # OUTPUT-COLORING red='\e[0;31m' green='\e[0;32m' NC='\e[0m' # No Color # FUNCTIONS # directoryExists - Does the directory exist? Looking into this outline it quickly becomes clear, that a trap handler can help us a lot in event-driven debugging with just adding a few lines to existing scripts without tampering command-line share|improve this question edited Mar 7 '11 at 13:41 Octavian Damiean 10.1k54160 asked Mar 7 '11 at 11:40 moata_u 71861523 5 Prefer $(foo) over backticks `foo`, because you can Bash Script Error Message This makes it difficult to tell if something went wrong just by looking at the textual output of a shell script.

Hit the Down Arrow button to ShellCheck it! But they all have in common, that it is hard to trap and trace unknown errors, especially if the script runs unattended. spectral norm of block-wise sums of matrices When was this language released? http://waspsoft.com/bash-script/bash-script-error.html Here's the verbose output: $ sh -x traptest.sh ++ mktemp -d /tmp/test.XXXXXX + my_temp_dir=/tmp/test.CU3OxO + my_log_file=/tmp/test.CU3OxO/output.log + my_out_pipe=/tmp/test.CU3OxO/output.pipe + mkfifo /tmp/test.CU3OxO/output.pipe + exec + tee /tmp/test.CU3OxO/output.log + tee_pid=10753 + 3 traptest.sh:

The two lines change the working directory to the name contained in $some_directory and delete the files in that directory.