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An error exit function Since we will be checking for errors often in our programs, it makes sense to write a function that will display error messages. bash scripting share|improve this question asked Sep 4 '09 at 9:51 samoz 20.8k39109168 add a comment| 6 Answers 6 active oldest votes up vote 225 down vote accepted Try this statement: So normally one exit is preferred (people looking at your code don't have to find the correct exit statement), however with error checking (especially at the start of a program/routine having in your example, if id -u == 0, which would mean that you are root.

true !true # No error this time, but no negation either. # It just repeats the previous command (true). # =========================================================== # # Preceding a _pipe_ with ! as bash will never get to the checking code if it isn't zero. How is the Heartbleed exploit even possible? The original script did not || the for loop. –RobertL Nov 6 '15 at 8:06 I just noticed I hadn't shown the set -o errexit command in my example

That is, the program's ability to handle situations in which something goes wrong. See below for an example: #!/bin/bash cd some_dir ./configure --some-flags make make install So in this case if the script can't change to the indicated directory then it would certainly not In this case, command-that-fails2 will not run. It's possible to write scripts which minimise these problems.

Race conditions It's worth pointing out that there is a slight race condition in the above lock example between the time we test for the lockfile and the time we create exit $?

#!/bin/bash COMMAND1 . . . Is it "eĉ ne" or "ne eĉ"? The last command executed in the function or script determines the exit status.

It is, though, a question of style and others can have their own opinions. –John1024 Nov 6 '15 at 7:37 1 works nicely! share|improve this answer answered May 20 '10 at 4:26 Matthew Flaschen 175k28368450 7 and you can add a newline after the && for readability –glenn jackman May 20 '10 at Aborting." 1>&2 exit 1 fi Here we check to see if the cd command is successful. Chapter 33.

If you add a -p option then mkdir will create all the parent directories before creating the requested directory. To explain how they work, I will quote from the bash man page: "The control operators && and || denote AND lists and OR lists, respectively. How do I help minimize interruptions during group meetings as a student? Exit status As you recall from previous lessons, every well-written program returns an exit status when it finishes.

This would be only the case if the compound command is executed in a context where set -e is ignored. One thing I have noticed is sometimes scripts use exit codes and sometimes they don't. If the script is meant to be run by another script, you may want to define your own set of status code with particular meaning. In general you are going to either want to specify an exit status exit 1 or set -e #!/bin/bash -e You can add error management in a variety of ways command

The return status of AND and OR lists is the exit status of the last command executed in the list." Again, we can use the true and false commands to see It merely tells the calling program that something went wrong. TERM Terminate - this signal is sent when someone sends the TERM signal using the kill command. The lockfile will be left there and your script won't run again until it's been deleted.

Why is the spacesuit design so strange in Sunshine? Using "set -e" as accepted above works fine. –pauldoo Sep 2 '15 at 19:45 add a comment| up vote 1 down vote In case script is calling subscript inside, the pipefail 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 up vote 3 down vote favorite I've been told in php it's preferred to avoid the use of the exit command as much as possible.

comments powered by Disqus Benjamin is a Systems Architect working in the financial services industry focused on platforms that require Continuous Availability. Please use the new version at LinuxCommand.org LinuxCommand Learningtheshell Writingshellscripts Script library SuperMan pages Who, What, Where, Why Tips, News And Rants Previous | Contents | Next Errors and Signals and And what about "double-click"? Notice the change () -> {} - the curly brackets do not spawn a subshell. (Search man bash for "subshell".) share|improve this answer edited Nov 24 '11 at 10:25 answered Nov

Make space between rows constant How to mount a disk image from the command line? https://www.gnu.org/software/bash/manual/bash.html#The-Set-Builtin Try a slightly adapted example posted by RobertL. An OR list has the form command1 || command2 command2 is executed if, and only if, command1 returns a non-zero exit status. bash shell shell-script scripting share|improve this question asked Nov 4 '11 at 15:01 Garrett Hall 7463910 add a comment| 4 Answers 4 active oldest votes up vote 32 down vote accepted

The problem is when the curl command fails, the loop retries the command five times - if all attempts are unsuccessful the for loop finishes and the main script resumes - To add our own exit code to this script, we can simply use the exit command. chroot=$1 ... What sense of "hack" is involved in five hacks for using coffee filters?

Is there any job that can't be automated? To do this make a copy of the data, make the changes in the copy, move the original out of the way and then move the copy back into place. asked 7 years ago viewed 194116 times active 2 months ago Linked 165 Checking Bash exit status of several commands efficiently 14 The difference between $* and [email protected] 5 Why do You want to be certain that something either happened correctly or that it appears as though it didn't happen at all.Say you had a script to add users.

In this case, the last run command is the echo command, which did execute successfully. Documentation From man bash: for (( expr1 ; expr2 ; expr3 )) ; do list ; done First, the arithmetic expression expr1 is evaluated according the rules described below under ARITHMETIC You can also use the slightly more readable set -o nounset. If N is omitted, the exit status is that of the last command executed.

Digital Diversity Can an ATCo refuse to give service to an aircraft based on moral grounds? more stack exchange communities company blog Stack Exchange Inbox Reputation and Badges sign up log in tour help Tour Start here for a quick overview of the site Help Center Detailed up vote 237 down vote favorite 50 I'm writing a script in Bash to test some code. Did Sputnik 1 have attitude control?

The easiest way to fix it is probably to just use an if: if [[ `id -u` != 0 ]]; then echo "Must be root to run script" exit fi share|improve If Dumbledore is the most powerful wizard (allegedly), why would he work at a glorified boarding school? This site is not affiliated with Linus Torvalds or The Open Group in any way. This will also work as expected, when you source the script.

Content is available under Attribution-Noncommercial-Share Alike 3.0 Unported unless otherwise noted. There are other constructs you could use: command if [ "$?"-ne 0]; then echo "command failed"; exit 1; fi could be replaced with command || { echo "command failed"; exit 1; line), but for me it does not work as expected with bash v3.2.57 on Mac OS X. For more on set -e, see Greg's FAQ #105. –John1024 Nov 6 '15 at 7:55 @John1024 Thanks.

Game of Life, a shorter story Is there any job that can't be automated? (KevinC's) Triangular DeciDigits Sequence How do I help minimize interruptions during group meetings as a student? Create a shell script called datatapebackup.sh: #!/bin/bash BAK=/data2 TAPE=/dev/st0 echo "Trying to backup ${BAK} directory to tape device ${TAPE} .." # See if $BAK exits or not else die # Set