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It does this displaying a # given error message, and exiting with an error code. Which is a useful feature when you're writing some common function that you will later source and use from other scripts. blog comments powered by Disqus Retrieved from "http://www.fvue.nl/w/index.php?title=Bash:_Error_handling&oldid=10109" Categories: BashFixed problems Navigation menu Personal tools Log in Namespaces Page Discussion Variants Views Read View source View history More Search Navigation Main Not the answer you're looking for? this contact form

The best example of handling errors in BASH I have found on the web was written by William Shotts, Jr at http://www.linuxcommand.org. Beware that set -e doesn't always kick in. 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 The "=" is a binary operator; that is, it expects two items to operate upon - one on each side.

Bash Error Message

Join them; it only takes a minute: Sign up Here's how it works: Anybody can ask a question Anybody can answer The best answers are voted up and rise to the for a in 1 2 3 do echo "$a" # done # Required keyword 'done' commented out in line 8. The trap must be the first command in the script.

Trapping signals

trapSpecifies an action on receipt of a signal; also In the end, the trap handler could be setup to send and email using both information from the intercepted trap and the logfile.

You can download some bash functions to do that from http://jimavera.cixx6.com/Carp.bash Perl programmers will feel right at home with these. (Sorry, I could not put the actual code in this post This page has been accessed 110,446 times. You can confirm the validity of this by trying it on the command line: [[email protected] me]$ number= [[email protected] me]$ See, no error message. Bash Error Trap For example, when you create a directory, if the parent directory doesn't exist, mkdir will return an error.

Instead shell script asks you, the author, to check individual program exit codes and branch as needed in case of an error. Empty variables Edit the script to change line 3 from: number=1 to: number= and run the script again. If not set, use `$?' function onexit() { local exit_status=${1:-$?} echo Exiting $0 with $exit_status exit $exit_status } # myscript # Allways call `onexit' at end of script onexit Caveat 1: command2 . . .' DEBUG" construct is #+ more appropriate in the context of a complex script, #+ where inserting multiple "echo $variable" statements might be #+ awkward and time-consuming. #

trap EXIT exit $?

The DEBUG argument to trap causes a specified action to execute after every command in a script. Bash Error 127 In practice, this means your once short script is going to get a little longer and a little more involved. You can either let the trap call error for you (in which case it uses the default exit code of 1 and no message) or call it yourself and provide explicit William Shotts, Jr's article Errors and Signals and Traps (Oh My!) is a good next step for learning more about how to approach error handling in shell scripts.

Bash Error Redirect

replace all local x=y with just x=y: # [CLEANUP=cleanup_cmd] run cmd [args...] # # `cmd` and `args...` A command to run and its arguments. # # `cleanup_cmd` A command that is By doing this, you can isolate which part of a program is causing (or not causing) a problem. Bash Error Message It also fails to check whether the user has permission to cd into it. –Ian D. Bash Error Output For example.: #!/bin/bash number=1 set -x if [ $number = "1" ]; then echo "Number equals 1" else echo "Number does not equal 1" fi set +x Previous | Contents |

Nathan Says: February 22nd, 2013 at 5:35 am So I copied the final script and pasted it into my text editor and saved it character-for-character and am getting an issue with http://waspsoft.com/bash-error/bash-error-code-255.html Again, for readability you may want to use set -o errexit. If the script is executed in a subshell, it's relative easy: You don't have to worry about backing up and restoring shell options and shell traps, because they're automatically restored when Natural construction Should indoor ripened tomatoes be used for sauce? Bash Error Code Check

set +e command1 command2 set -e On a slightly related note, by default bash takes the error status of the last item in a pipeline, which may not be what you trap exit ERR # ! ! ! I didn't know that double quotes expanded the variable in this case. –Mechaflash May 30 '12 at 14:23 echo hello | grep foo doesn't seem to throw error for navigate here Remember that "[" is an abbreviation for the test shell builtin.

function catch_sig() { local exit_status=$? Bash Error To Stdout Another disadvantage of using traps is bad composability, as you risk overwriting previous trap that might be set earlier up in the caller chain. This tells bash that it should exit the script if any statement returns a non-true return value.

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:

Advanced Bash-Scripting Guide: Prev >Next

Chapter 32. So, here's my hint: file content: lib.trap.sh lib_name='trap' lib_version=20121026 stderr_log="/dev/shm/stderr.log" # # TO BE SOURCED ONLY ONCE: # ###~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~## if test "${g_libs[$lib_name]+_}"; then return 0 else if test ${#g_libs[@]} == 0; trap SIGNAL restores the functioning of SIGNAL once more. Bash Error Level At a minimum, the gotchas in question should be well-understood. –Charles Duffy Sep 11 '12 at 13:17 2 set -e -o pipefail -u # and know what you are doing

sleep $interval done; } & # Start a progress bar as a background process. echo '--> cleanup' return $exit_code } echo '<-- outer' } inner() { set -e echo '--> inner' some_failed_command echo '<-- inner' } outer Here is the generic function that builds upon Export to PDF Export to Text 3 Responses to "Trap Errors, Exit Codes and Line Numbers within a Bash script (and some output redirection, too)" george youn Says: January his comment is here 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.

rollback() { del_from_passwd $user if [ -e /home/$user ]; then rm -rf /home/$user fi exit } trap rollback INT TERM EXIT add_to_passwd $user cp -a /etc/skel /home/$user chown $user /home/$user -R You can check for files with files open by using lsof.