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It would be nice if you could fix these problems, either by deleting the lock files or by rolling back to a known good state when your script suffers a problem. Use set -u How often have you written a script that broke because a variable wasn't set? I like to include the name of the program in the error message to make clear where the error is coming from. This tutorial has been deprecated! this contact form

asked 5 years ago viewed 51705 times active 10 months ago Linked 192 What does set -e mean in a bash script? Is 8:00 AM an unreasonable time to meet with my graduate students and post-doc? If the expression is of the form "p AND q", and p is evaluated to be false, there is no reason to look at q. COMMAND_LAST # Will exit with status of last command.

Bash Exit Status Variable

But what happens if the directory named in $some_directory doesn't exist? If a function "succeeds" it returns 0 and if it "fails" it returns non-zero therefore && might be expected to evaluate when the first half returned non-zero. echo 'Bad: has not aborted execution on syntax error!' Result: $ ./sh-on-syntax-err ./sh-on-syntax-err: line 6: #: syntax error: operand expected (error token is "#") status 1 Bad: has not aborted execution To overcome this use { } The last two changes are required by bash.

share|improve this answer answered Dec 7 '10 at 21:14 DGH 4,89611423 9 In unix, success is always 0. It contains the current # line number. I've tried: my_command && (echo 'my_command failed; exit) but it does not work. Bash If Also note that ( does not seem right to me in bash, but I cannot try from where I am.

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 Bash Exit Code inverts the exit status returned. This becomes more important as your programs get more complex and you start having scripts launching other scripts, etc. Sample Script: #!/bin/bash touch /root/test echo created file The above sample script will execute both the touch command and the echo command.

In this case, the last run command is the echo command, which did execute successfully. Bash Functions share|improve this answer edited Jul 8 '13 at 19:05 answered Jul 8 '13 at 18:48 gniourf_gniourf 1,291412 I meant the absence of such feature is a problem. command; then echo "command failed"; exit 1; fi What if you have a command that returns non-zero or you are not interested in its return value? Note the inclusion # of the LINENO environment variable.

  1. exit / exit status

    #!/bin/bash echo hello echo $? # Exit status 0 returned because command executed successfully.
  2. listing6.inc.sh # Source listing6.inc.sh # $ foo # Run foo() # foo_init # Entered `trap-loop' # trapped # This is always executed - with or without a trap occurring # foo_deinit
  3. perhaps this must be reported as a bug/wish to bash developers The answer is definitely no!
  4. Furthermore, "the rules change from one Bash version to another, as Bash attempts to track the extremely slippery POSIX definition of this 'feature'".
  5. true echo $? #echo trap_handler $exit_status } # trap_exit_handler() # An erroneous command will trigger a bash error and, because # of 'set -e', will 'exit 127' thus falling into the
  6. In that case, the shell will interpret the variable as empty and the cd succeed, but it will change directories to the user's home directory, so beware!

Bash Exit Code

Unfortunately it means you can't check $? environment variable. $? Bash Exit Status Variable echo 'Bad: has not aborted execution on syntax error!' Result: $ ./sh-on-syntax-err ./sh-on-syntax-err: line 6: #: syntax error: operand expected (error token is "#") status 1 Bad: has not aborted execution Bash Set E there are dark corners in the Bourne shell, and people use all of them.

--Chet Ramey

The exit command terminates a script,

listing6.inc.sh # Source listing6.inc.sh # $> foo # Run foo() # foo_init # Entered `trap-loop' # trapped # This is always executed - with or without a trap occurring # foo_deinit weblink my_command || { echo 'my_command failed' ; exit 1; } share|improve this answer answered Sep 29 '10 at 14:34 Benoit 46.8k12128190 IIRC, you need semicolons after each of the use the [] for that. This is Bash's way of giving functions a "return value." [1]

Following the execution of a pipe, a $? gives the exit status of Bash Trap

If you add a -p option then mkdir will create all the parent directories before creating the requested directory. The advantage of this approach is that it's automatic: you don't run the risk of forgetting to deal with an error case. Don't let this happen to you! navigate here Actions such as printing to stdout on success and stderr on failure.

Sourced in current shell If the script is sourced (included) in the current shell, you have to worry about restoring shell options and shell traps. Bash Error Handling To add our own exit code to this script, we can simply use the exit command. echo exit 113 # Will return 113 to shell. # To verify this, type "echo $?" after script terminates. # By convention, an 'exit 0' indicates success, #+ while a non-zero

From the bash manual, set -o errtrace or set -E: If set, any trap on `ERR' is inherited by shell functions, command substitutions, and commands executed in a subshell environment.

The instance will be terminated for you when the script exits - even if some uncaught error causes it to exit early. (Just make sure to block until the image creation Trap in executed script When a script is executed from a shell, bash will create a subshell in which the script is run. after every statement to catch syntax errors. (I expected such safe behavior from a sensible programming language... Bash File Exists The basic code structure is like this: #!/bin/bash function finish { # Your cleanup code here } trap finish EXIT You place any code that you want to be certain to

I accepted a counter offer and regret it: can I go back and contact the previous company? up vote 99 down vote favorite 30 I am a noob in shell-scripting. A careful reading of the output of help set shows: -e Exit immediately if a command exits with a non-zero status. his comment is here The secret sauce is a pseudo-signal provided by bash, called EXIT, that you can trap; commands or functions trapped on it will execute when the script exits for any reason.